Hi Everyone,
Its that time of year again and I’m looking forward to starting this blog again. Donald Sutherland, who posts over at American Weather Forums does a great job in providing some insight toward future winter weather patterns. I’ll continue to update this periodically the next several months.
***********************************************************************************************************************************************
Posted 19 March 2016 – 6:19 PM
Some of the computer guidance, including the 3/19/2016 12z GGEM, RGEM and UKMET; 3/19/2016 12z EPS; and, 3/19/2016 18z GFS and RGEM indicate that a storm will bring a swath of potentially 4” or more snow from portions of the northern Middle Atlantic region into New England.
Since 1950, there have been 20 such storms. Two of those storms brought 4” or more snow to Boston and New York City while one of those storms brought 4” or more to New York City and Philadelphia.
***********************************************************************************************************************************************
Posted 4 March 2016 – 1:39 PM
Last night into today, a storm moving off the lower Mid-Atlantic coast deposited a swath of snow across the Middle Atlantic region. For the most part, snowfall amounts were fairly light (2″ or less). However, a few locations saw greater amounts including Cape May, NJ: 6.5″; Milton, DE: 5.8″; and, Princess Anne, MD: 6.7″.
Big changes lie ahead on account of the expected development of an extreme trough centered near Mexico’s Pacific Coastline (more than 5 standard deviations below normal) and a ridge with positive height anomalies of 1-2 standard deviations above normal in the East during the 3/8-10 period. The result should be the warmest readings so far this year in parts of the Great Lakes Region to the Middle Atlantic and New England areas.
***********************************************************************************************************************************************
Posted 29 February 2016 – 10:19 AM
Today’s AO figure was -0.378. Based on the final December and January values and preliminary February values, the AO was neutral to slightly positive for Winter 2015-16. The preliminary average is +0.007.
The distribution of values is below:
With the wave lengths continuing to shorten courtesy of the seasonal evolution, one needs stronger blocking, all other variables being equal, to produce the cold anomalies similar to those in February. For example, for New York City, the March 1-10 temperature anomalies for an AO of -2.999 to -0.001 is similar to those for an AO > 0. An AO of -3.000 or below is decidedly cooler (nearly 6° cooler).
One variable that could offset a positive AO is the EPO. Last March, the EPO was negative to strongly negative for much of the first 20 days of the month. This March, it is forecast to be positive through at least the first 10 days of the month. At the same time, the AO is forecast to bottom near -2.000 before rising toward possible positive values by March 10.
Just looking at the state of those two indices and typical 500 mb patterns associated with them would argue for a warming trend to roll across the CONUS near March 7 +/- a few days with the potential for a bout of much above normal readings. There remains a risk that the second half of the month could witness the development of sustained ridging covering parts of eastern North America including Ontario, Quebec, the Midwest, Mid-Atlantic, and New England areas. If so, the second half of the month could be very warm relative to normal. Such ridging developed in late March in 1998 as a super El Niño was winding down. For now, it’s a little soon to be sure about such an outcome this March, but the potential is there, especially if blocking dissipates and does not rebuild.
For now, my guess is that a large part of the Midwest and eastward will probably wind up experiencing a much warmer than normal month (anomalies of 3° or more above normal). The PDO+ will likely continue to promote a PNA+ pattern, which would bring continued warmer than normal readings to the Pacific Northwest.
***********************************************************************************************************************************************
Posted 23 February 2016 – 11:18 AM
During the November 19-22, 2015 period, a significant early season storm brought heavy snow across parts of the Midwest into the Great Lakes region. Chicago picked up 11.2” and Detroit received 6.0”. Howell, MI was buried under 15.5”.
An even stronger storm will bring heavy snow to the south and east of the November storm’s axis of heaviest snows. As a result, parts of northwestern Indiana into Michigan will likely see the biggest accumulations. The 12z run of the RGEM suggests the potential for 10” or more snow exists in parts of that region.
At the same time, unseasonably warm air appears very likely to surge up the Eastern Seaboard. During the November storm, temperatures rose into the 50s as far north as southern New England with middle 50s reported in such cities as New York and Philadelphia. The push of warm air could be stronger this time around on account of the greater forecast intensity of the storm. As a result, it still appears likely that Baltimore, Richmond, and Washington could see temperatures reach or exceed 60°. Readings of 70° or above are possible from parts of Virginia southward. Temperatures in the 50s could reach as far north as Portland, Maine. Moreover, parts of the Coastal Plain could pick up 1.50”-3.00” precipitation over the next 60 hours.
The 12z GFS MOS forecast highest temperatures for the 2/24-25 period for select cities are:
Baltimore: 60°
Boston: 52°
Bridgeport: 51°
Charleston, SC: 77°
New York City: 57°
Newark: 56°
Norfolk: 70°
Philadelphia: 58°
Portland: 51°
Providence: 51°
Raleigh: 72°
Richmond: 71°
Savannah: 78°
Washington, DC: 62°
***********************************************************************************************************************************************
Posted 19 February 2016 – 10:19 AM
The February 19 preliminary Arctic Oscillation figure was +1.609 bringing the winter-to-date AO average to +0.057. With today’s being the 46th AO+ day, winter 2015-16 is assured to have more than 50% of days with AO+ values. Even as the ensembles take the AO negative next week, somewhere close to 55% of days during winter 2015-16 will wind up with AO+ values. It remains likely that the winter AO average will also be somewhat positive unless the ensemble members showing the deeper blocking verify.
At present the AO will likely be shifting negative around the 2/24-25 timeframe. About half of ensemble members are negative at that time and around half are positive.
As that is happening, the computer guidance is in good agreement about the development of a potentially significant storm. Assuming the AO forecast is reasonably accurate, the timing of the development of the blocking will probably be a little late to promote the kind of storm that could bring a significant snowfall from Washington, DC to Boston. Instead, interior sections with perhaps those somewhat to the south and east of the heaviest snowfall during the February 15-16 storm would more likely be favored. Some snow could not be ruled out for the coastal plain, but the focus of heavier snows would be inland.
With March approaching, it makes sense to examine how the AO has evolved relative to past strong El Niño winters. The closest match for the 15-day period ending February 25 is 1998.
March 1998 featured a persistent trough in eastern North America that gradually shifted south and westward after mid-month. The closing portion of March saw the development of a ridge over the eastern CONUS and trough along the West Coast.
There was also a close match with respect to the PNA. February 1998 saw 26 of 28 days with a PNA+. So far, February 2016 has had 17/19 days with PNA+ values and, if the ensemble forecasts are correct, would wind up with 27/29 days of PNA+ values. Both winters featured a strong and persistent PDO+, which favors the PNA+. March 1998 featured predominantly PNA+ values, with 27 of 31 days having such values. The closing 10 days of March saw the only PNA- values.
Some differences should be noted, as well.
1. The current strong El Niño is basinwide and experiencing the strongest cooling in the eastern ENSO regions; 1997-98 was an East-based ENSO event. During that event, Regions 3.4 and 4 were cooling faster than Region 1+2.
2. The current guidance forecasts somewhat earlier development of blocking than during late February 1998.
3. The current guidance forecasts that the blocking will be stronger than that which occurred from the end of February into March of 1998.
4. Much higher amplitude MJO during February
So, at this point in time, one can cautiously argue for the development of a trough in eastern North America and possibly a fairly deep one. This trough could persist through at least the first 10-15 days of March. Then, at some point, it could weaken and/or migrate westward. Much will depend on the strength of the forecast blocking and its evolution.
For now, it’s still a little soon to be sure, but there would be a risk of a dramatic pattern change late in the month. Before then, the active subtropical jet should provide periodic opportunities for frozen precipitation from the Plains States eastward to the Middle Atlantic and New England regions.
It should be noted that the latest CFSv2 begins to develop ridging in the East during week 4. That could be premature, but something that would be plausible during Week 5 or 6 if the evolution of blocking is reasonably similar to what took place in 1998 while allowing for stronger and somewhat longer-lasting blocking. The biggest uncertainty concerns the MJO. During March 1998, the big change to ridging occurred when the MJO moved in Phases 1 and then 2. Phase 2 closed the month and it was the only high-amplitude MJO during March. Assuming the MJO remains at predominantly high amplitudes as has been the tendency this winter (average amplitude through 2/17: 1.747 vs. DJF 1997-98 figure of 1.113), MJO forcing will play a larger role in shaping the outcomes.
***********************************************************************************************************************************************
Posted 16 February 2016 – 11:19 PM
To illustrate the potential extremes of the upcoming warmth in parts of the Plains States, the 2/17 0z GFS MOS forecasts a high temperature of 81° for Rapid City on February 18. That would smash the existing record of 66°, which was set in 1983. It would also be the earliest 80° reading on record by 3 weeks, if it verifies.
***********************************************************************************************************************************************
Posted 16 February 2016 – 9:43 AM
Record Heat Likely in the Plains…
What has been a winter of extremes continues. So far highlights include:
- An historically warm December in large parts of eastern North America equivalent to among the 10 warmest Novembers on record.
- A late December blizzard that buried parts of New Mexico under more than 20” snow along with extensive flooding along the Mississippi and Missouri Rivers.
- A late January blizzard that brought record snowfall to Baltimore and the 2nd biggest snowfall on record to New York City
- A Valentine’s Day Arctic outbreak that produced some of the coldest readings in nearly 50 years in parts of southern New England and New York City’s first subzero reading since January 19, 1994
- An exceptionally warm Arctic winter that has seen record low Arctic sea ice extent figures on more than half the days during the January 1-February 15 period.
The latest GFS ensembles indicate that 2σ or greater positive height anomalies will move through the Plains states Tuesday through Thursday producing an area of temperature anomalies of 2.0σ to 3.0σ above normal.
Record high temperatures for February 18:
Albuquerque: 71°, 1981
Denver: 71°, 1930
Lincoln: 70°, 1930
Rapid City: 66°, 1983
Wichita: 74°, 1930
Another round of excessive warm anomalies is forecast to develop in the western third of the U.S. for the February 22-25 period. That region will likely continue to experience above to much above normal readings through the remainder of February.
Finally, the Arctic Oscillation is forecast to dive to negative and perhaps strongly negative values in the extended range. The latest ensemble forecasts take it negative around 2/24 +/- 1 day. This could have implications as the closing week of February and perhaps the opening week of March could be stormy. A negative AO could have the largest implications for the Middle Atlantic region, as more than two-thirds of that region’s significant (6” or greater) snowstorms have occurred with an AO-.
Courtesy of the continuing strong PDO+, the PNA is likely to remain positive to strongly positive for the remainder of February and likely into at least the start of March. This situation could also favor a trough in the East, though shortening wavelengths could lead to the trough’s migration toward the Midwest over time.
***********************************************************************************************************************************************
Posted 12 February 2016 – 10:00 AM
A few quick thoughts…
Today’s AO value was -1.807. The current period of blocking coincides very closely with the severe cold that will be unfolding from today into the weekend.
Afterward, the AO is forecast to rebound rapidly to positive values at a time a storm is forecast to impact parts of the eastern U.S. and Canada. During the second half of February, AO- values typically correspond with significant (6″ or greater) snowfalls on the coastal plain. For example, 75% of such storms that brought 6″ or more snow to two or more of the major cities in the Middle Atlantic region northward (Washington, DC, Philadelphia, New York, and Boston) occurred when the AO was negative. In this case, it is forecast to have returned to positive values.
As a result, the more typical outcome would be an interior storm that brings significant snowfall amounts well inland. A blend of the latest ECMWF, GFS, and CMC snowfall forecasts is very consistent with that more typical scenario. Some snow could still accumulate in the major East Coast cities with Washington and Baltimore more favored than New York or Boston for a few inches, but the major snows will likely fall well west of the coastal plain.
It should be noted that the 2/12 12z run of the NAM offers a snowier “second opinion” about that storm.
Finally, in the extended range near the end of February, the AO is forecast to go negative. If that forecast verifies, the eastern half of the U.S. and southern Canada could again see more cold return. Whether or not such a pattern change might create the opportunity for a stormy March, as has occurred on some occasions during waning El Niño events will need to be watched if the AO heads negative.
***********************************************************************************************************************************************
Posted 11 February 2016 – 9:55 AM
With the calendar now approaching mid-February and meteorological winter nearing an end (that does not mean that winter weather will be finished), it’s a good time to look at how the Arctic Oscillation (AO) has fared this winter. As noted on repeated occasions, the AO cannot accurately be forecast for more than a few weeks in advance. Even the leading effort based on the Snow Advance Index (SAI) falls short.
At this point in time, it is now likely that the Snow Advance Index (SAI) forecast of a negative winter AO, the third consecutive such forecast, will again be incorrect. That does not mean that it does not add value, as there was a period of severe blocking that occurred in January and another period of blocking that has just commenced. The overall outcome that appears likely suggests that the SAI has some predictive value, but other variables outside the index also have predictive value and those other variables may explain more of what happens, at least in some winters.
Through today, here’s where things stand:
AO Average: +0.072
% Days AO > 0: 58%
% Days AO +1.000 or above: 41%
% Days AO +2.000 or above: 18%
% Days AO +3.000 or above: 8%
% Days AO < 0: 42%
% Days AO -1.000 or below: 30%
% Days AO -2.000 or below: 22%
% Days AO -3.000 or below: 14%
Lowest AO Value: -4.898, 1/16/2016
Highest AO Value: +4.503, 12/22/2015
Maximum % Days AO- (if February 12-29 all have AO- values): 54%
Maximum % Days AO+ (if February 12-29 all have AO+ values): 66%
In order for the winter AO to average 0.000, the AO would need to average -0.292 for the February 12-29 period. Right now, the ensemble forecast favors a return to AO+ values just after mid-February. In turn, that outcome suggests that a positive AO average is very likely for meteorological winter and a majority of days during that period will wind up featuring AO+ values.
If the AO winds up with a positive average for the December-February period, winter 2015-16 would be the 4th out of the last 5 winters to feature an AO+ average:
2011-12: +0.670
2012-13: -1.126
2013-14: +0.188
2014-15: +0.843
2015-16: Near +0.100 (?)
In terms of extreme AO values (-3.000 or below or +3.000 or above), winter 2015-16 featured a return of severe negative values for the first time since winter 2012-13. It also saw a higher percentage of days with such negative or positive values than any of the preceding four winters.
***********************************************************************************************************************************************
Posted 8 February 2016 – 12:18 PM
The GFS ensembles have been forecasting a shot of Arctic air with readings 1.5 to 2.5 standard deviations below normal across parts of the Midwest and 2.0 to 3.0 standard deviations below normal in parts of the northern Middle Atlantic and New England areas in recent days. Select data for Boston, Chicago, Detroit, New York City, Philadelphia, and Washington, DC is below:
Back to top
Quote
***********************************************************************************************************************************************
Posted 7 February 2016 – 11:03 AM
If one examines the forecast 500 mb pattern at 48 hours and compares it with the 500 mb pattern of February 10, 2015 (both cases featured an AO+), one finds some similarities and also some differences:
Similarities:
• Deep trough in the Southeast
• Positive to very positive 500 mb height anomalies over the top of the trough
Differences:
• The trough is centered west-northwest of its 2015 position
• There is a weakness in the positive 500 mb height anomalies close to where the most positive anomalies were centered in 2015
• The trough is also forecast to be deeper than it was in 2015
These differences are somewhat subtle, but they imply an area of snowfall that would be more southwest-northeast oriented than the largely east-west orientation of 2015. They also imply that appreciable snows will likely fall farther to the south and west than those in 2015. Southeast Massachusetts will still very likely feature the heaviest accumulations. But significant accumulations (6” or more) might well extend into southern Connecticut and parts of Long Island. New York City (0.1” in 2015) and Newark (0.2”) might still have the potential to pick up several inches of snow.
Finally, a quick look at snowstorms that commenced in the 2/8-10/1950-2015 period with a positive AO as high as +2 provided the following distribution of outcomes for Boston and New York City:
Boston:
1” or more: 43%
2” or more: 29%
4” or more: 14%
6” or more: 14%
10” or more: 14%
15” or more: 7%
New York City:
1” or more: 43%
2” or more: 29%
4” or more: 7%
6” or more: 7%
10” or more: 7%
15” or more: 0%
***********************************************************************************************************************************************
Posted 5 February 2016 – 2:23 PM
With the GFS showing continued cold after mid-month, the ECMWF continues to oscillate wildly between cold and warm anomalies in its extended range. The ECMWF is highlighting uncertainty and the continued cold following mid-month appears very much to be on the proverbial table.
it’s still premature to assume that the very warm weekly guidance for the period beyond mid-February will necessarily verify. Odds increasingly appear that it won’t.
A lot will depend on whether blocking is sustained or redevelops. The most recent GFS ensembles suggest more blockiness than had been shown even a few days ago. Hence, any warm up after mid-month relative to normal, if it occurs, may be delayed or even short-lived. Should the blocking break down as had previously been indicated, then the prospects of a sustained warmer period would increase.
Right now, perhaps the safest route is to assume that there will be sufficient and sustained cold to bring the exceptionally warm anomalies across much of the eastern two-thirds of the country down toward levels closer to January’s figures given the evolution of the strong El Niño (post #211). Put another way, the very warm weekly guidance from a few days ago increasingly appears to have been overdone and perhaps substantially overdone.
***********************************************************************************************************************************************
Posted 3 February 2016 – 10:13 AM
The storm that brought a swath of snow across the Plains States is moving into Canada. Its associated warm front will bring a large area of moderate to heavy rainfall across the U.S. East Coast today.
In the larger scheme of things, the Arctic Oscillation, currently at +0.467 is forecast to go negative to possibly strongly negative in 3-5 days. During the last period of strong blocking, a blizzard brought near record to record snowfall amounts across parts of the Middle Atlantic region. Some of the guidance suggests that parts of the East could again be impacted by an appreciable to possibly significant snowfall during the forecast round of blocking.
The ensemble guidance has been consistent and in agreement that an Arctic outbreak will likely occur near February 10 +/- 1-2 days and then spread eastward from the Plains States to the East Coast. That cold air should be sufficient to dent the impressive warm anomalies that have been accumulating in the early part of February. For example, in New York City, through 10 am today, the February anomaly is running at 14.2° above normal. To put this anomaly into context, if the remaining 26 days of February had normal temperatures, the monthly anomaly would wind up +1.5°. An average anomaly of 1.6° below normal for the 2/4-29 period would be required to produce a normal monthly mean temperature. So far, similar warmth has prevailed across much of the eastern half of the United States.
This raises the question as to whether the groundhogs that failed to see their shadow yesterday (a forecast of an early spring) were looking ahead or whether they were reacting to the exceptionally warm start to February.
As that the cold moves into the eastern half of the U.S., the western third of the United States and British Columbia, which have started off very cold should experience a warming trend.
After mid-February, the blocking is forecast to dissipate with a positive to possibly strongly positive AO returning. As a result, a warming trend could develop from the Plains States and then expand eastward during or just after mid-February. What happens beyond that will depend on whether blocking returns. The forecast MJO suggests that the forecast AO+ might last at least 5-10 days, but that’s speculative right now.
Nevertheless, at this point in time, it appears that the AO will wind up slightly positive overall for meteorological winter. In addition, somewhere around 55% +/- 5% of days will likely have seen a positive AO.
Finally, if one takes the trimmed GFS analog pool and rolls them ahead to February 20, milder than normal readings seem somewhat more likely than cooler ones for such cities as Chicago and Washington. That kind of outcome would be consistent with a positive AO during that date. A few of the cases did produce a cold shot from the Upper Plains into the Midwest, so there is still a fairly large degree of uncertainty regarding the evolution of events after the forecast Arctic shot.
***********************************************************************************************************************************************
Posted 1 February 2016 – 8:55 AM
Incorporating today’s weekly ENSO region data, the change in the mean January ENSO Region 1+2 anomaly has been approximately 0.50°C cooler than the change in the ENSO Region 3.4 anomaly. ENSO Region 1+2 has seen its average anomaly fall from near +2.15°C to about +1.40°C (OISST weekly data). In contrast, Region 3.4 has seen its average anomaly drop from approximately +2.80°C to near +2.55°C.
Given the tendency of some Central Pacific-oriented El Niño events to produce widespread cold across North America in February, one might be tempted to expect a much more widespread cold relative to normal than the preceding January.
In fact, the evolution of ENSO anomalies that has occurred suggests that the spatial distribution of temperature anomalies and, to a lesser extent, their magnitude should be pretty similar to January.
Since 1950, there have been four cases with moderate or strong El Niño events that saw the January Region 1.2 anomaly cool by 0.30°C or more than the Region 3.4 anomaly from their December averages.
If one looks at the outcomes, one finds that the subtropical jet tends to have a somewhat larger impact on temperature anomalies in the southern tier than January, but the overall distribution of anomalies is not much different overall across North America. In other words, the kind of evolution that is underway is a sort of “preserver” of the January anomalies.
With the exception of the circled region, the 1/31 CFSv2 forecast for February was quite similar to the January outcome. Moreover, if one looks at the latest ensemble guidance, the first 10 days of February appears likely to build up an impressive warm anomaly in some of the areas that wound up with warm anomalies during January. The 10-15-day EPS outlook favors a large cold shot to eastern North America that would then dent but not erase those warm anomalies. What happens afterward will depend largely on whether blocking can be sustained.
The February 1 Arctic Oscillation (AO) value was +2.186. As a result, the AO average for meteorological winter to date has swung back to slightly positive values (+0.034). However, strong blocking is forecast to develop over the next 7-10 days. Back in January, blocking predominated during the January 2-22 period with the strongest blocking present during the January 9-19 timeframe. If the GFS ensembles are reasonably accurate, the strongest blocking could again be present during a similar period in February as was the case in January.
As Yogi Berra once suggested, perhaps February will prove to be “déjà vu all over again.” Certainly, the ENSO evolution temperature anomalies lend some weight to such an outcome and the timing of the forecast blocking may, as well.
***********************************************************************************************************************************************
Posted 29 January 2016 – 9:47 AM
The Return of the Strongly Positive AO…
This morning, the Arctic Oscillation stood at +3.900 on this 60th day of meteorological winter. The AO has averaged -0.102 through today. Over the next 3-5 days, the average for meteorological winter will very likely go positive, where it had been until January’s strong blocking episode. So far, 55% of days have had a positive AO with 42% experiencing an AO of +1 or above. 45% of days saw a negative AO with 35% featuring an AO of -1 or below.
The strong blocking that developed earlier this month has often been a precursor to predominant blocking in February. However, the big rebound that has now taken place is a proverbial fly in the ointment. Most cases that saw the AO rebound to strongly positive values in the January 25-February 10 timeframe featured little blocking in February. The new GFS ensemble forecast now has far fewer ensemble members pointing to a return of blocking in early February.
Compounding matters is the failure of a significant or major stratospheric warming event to appear in late January. Instead, a relatively minor event will take place over the next 3-4 days with the stratosphere again cooling afterward. Some wave-breaking activity will attempt to displace the polar vortex.
Nevertheless, Winter 2015-16 may not fit neatly into what has taken place in the past, even if the AO+ predominates for at least the first half of February or longer. The super El Niño event is only slowly fading after having peaked in mid-to-late-November. The best ENSO forcing is west of where it was during the 1997-98 super El Niño event. The PDO+ persists favoring a PNA+.
Put another way, scenarios other than widespread warmth across much or all of North America are plausible, though . There is variability among the cases. For example, 1976 featured widespread warmth in February. In contrast, despite an extremely positive AO, February 1989 did not.
Looking more closely, only three of the featured cases saw a PDO+ in February: 1981, 1982, and 1993. Again, there was variability among those cases.
Where there is greater consensus is that a predominantly positive AO could limit snowfall opportunities in the Middle Atlantic region. However, there is only a single El Niño case in the mix and that El Niño event was a weak one. Therefore, even this stronger consensus among the cases is subject to a fairly large degree of uncertainty.
All said, at least for now, I am cautiously suggesting that the outlook for a blocky February has diminished somewhat (but probably not as greatly as implied by the above historic cases), though considering the earlier January block, it remains possible. The latest EPS continues to support that idea. The specific implications remain to be determined and variables such as the EPO, PNA, and ENSO may either amplify the impact of any reduced blocking or even counter it. For now, it still appears that early February warmth will give way to a colder pattern, starting first in the central portion of North America then moving eastward. Whether that cold will lock in for more than 10-14 days will depend on factors, including but not limited to renewed blocking (which now appears somewhat less likely than even a week ago).
***********************************************************************************************************************************************
Posted 26 January 2016 – 10:04 AM
Moderation Looms but February May Still Have Snowstorm Potential…
Today is the 57th day of meteorological winter. So far, January has featured a remarkable turnaround in temperatures from December in the areas that experienced historic warmth. Some of that region is currently running somewhat colder than normal while other parts are somewhat above normal.
]
Aside from the temperature reversal, which would be notable by itself, there was also a major Mid-Atlantic blizzard during the January 22-24 period. The Washington, DC area (e.g., National Zoo), Baltimore, Philadelphia, and New York City received more than 20” snow.
Over the next 5-10 days, a milder pattern is likely to prevail. However, toward the end of that timeframe, colder air could return to western portions of North America and then begin to expand eastward. The operational GFS and ECMWF and their ensembles are in good agreement with such a scenario.
The longer-term for February is less certain. The 1877-78 super El Niño saw a similar reversal in temperatures in January only to witness a partial return of the widespread anomalous warmth in February. The 1982-83 super El Niño experienced a similar January temperature reversal with the February temperature profile largely resembling the January one.
In terms of blocking, the AO fell to -4.916 on January 17. Climatology favors a negative AO for February and the probability of a negative AO is higher than climatology in cases when the AO fell below -3.500 during the January 15-25 timeframe. Nevertheless, probabilities should not be read in a deterministic fashion, so there is a risk, albeit lower than climatology, of a positive February AO.
In coming days, a minor stratospheric warming event is forecast by the ECMWF. However such an event is forecast to fall well short of what one witnesses during a typical sudden stratospheric warming event (SSW) and it is not forecast to propagate downward into the troposphere. Hence, as was the case in January when a super Kara Sea-centered ridge displaced the polar vortex yielding a strongly negative AO, one will likely need to look to the troposphere for the largest impact on the AO’s evolution.
The ongoing PDO+ suggests that the persistent PNA+ pattern that has prevailed during meteorological winter (88% of days have seen a PNA > 0) will likely predominate through at least the first half of February and perhaps longer.
The super El Niño continues to fade, particularly in Region 1+2. The change in anomalies by ENSO region during the past 4 weeks is as follows: Region 1+2: -0.7°C and Regions 3, 3.4, and 4: -0.2°C. The cooling should continue and will likely accelerate a little in coming weeks. Nevertheless, strong El Niño conditions are likely to persist through February.
So, at this point in time, given all of the above data, it is plausible that February could see monthly anomalies wind up above normal in much of North America starting somewhere between 35°N and 40°N latitude (but not so warm to preclude opportunities for snowfall, especially when blocking is present during which colder anomalies could also prevail). The continued strong El Niño favors an active subtropical jet and possible storminess. The potential for at least some degree of blocking (which has generally been strong when it has been present) coupled with a PNA+ argues that at least some of this storminess could bring meaningful snow across some parts of North America (especially from the southern tier toward the Middle Atlantic and perhaps southern New England regions.
There remains a risk, though a smaller one, of a sort of “worst case” scenario similar to the evolution of winter 1877-78 whereby much of North America would return to a warmer than normal temperature regime. The latest run of the CFSv2 is highlighting that potential. This is something that will need to be watched. If one does not witness a return of the EPO- and later, AO-, the probability of the warmer outcome would increase.
***********************************************************************************************************************************************
Posted 22 January 2016 – 3:06 PM
At 3 pm, moderate snow was falling in Washington, DC.
https://www.senate.go…eral/capcam.htm
***********************************************************************************************************************************************
Posted 22 January 2016 – 8:24 AM
Historic Blizzard Imminent for Middle Atlantic Region…
At 8 am, the first impressive wave of precipitation had moved into southern sections of Virginia while farther north mid-level clouds were mostly obscuring the sun in Washington, DC with only a few streaks of orange left in the sky.
These developments mark the early stages of what will likely be an historic and crippling blizzard for such cities as Washington and Baltimore. Both cities could approach or exceed their modern snowfall records. 30″ or greater snowfall amounts are likely across parts of the area. A widespread outbreak of thundersnow appears likely given some of the soundings. In the Blue Ridge where orographic lifting could enhance snowfall rates, a few spots could approach or exceed 40″.
To illustrate how tremendous the potential QPF is, below are the last four figures for Washington, DC (DCA) from the GFS:
1/21 12z: 2.69″
1/21 18z: 2.44″
1/22 0z: 3.27″
1/22 6z: 3.64″
Not only has the model consensus remained remarkably consistent about the potential of a huge snowfall, one has seen some of the guidance expand the precipitation field a little farther to the north. Such guidance includes the 6z GFS, 0z ECMWF, 6z RGEM, and 0z UKMET.
My final estimates are as follows:
Baltimore: 20″-30″
Boston: 2″-4″
Bridgeport: 6″-12″
New York City: 8″-14″
Newark: 10″-15″
Philadelphia: 14″-20″
Sterling: 24″-36″
Richmond: 8″-14″
Washington, DC: 24″-36″
White Plains: 6″-12″
A small deviation in the storm’s track could still result in a large increase in snowfall on the northern extent. For example, even a 25-30-mile shift northward could result in New York City’s picking up closer to 15″ snow than 10″.
***********************************************************************************************************************************************
Posted 21 January 2016 – 8:24 AM
Overnight, details concerning what will likely be a major-to-historic Middle Atlantic snowstorm have come into greater focus. Right now, the two dominant aspects of the guidance are persistent fairly strong confluence and the interaction of system’s coming into the Pacific Northwest and the eastern trough that will likely limit the storm’s ability to gain latitude as that incoming system serves to “kick” the storm out to sea. Whether the storm reaches North Carolina’s Outer Banks and then heads out to sea or reaches the northern Delmarva Peninsula/southern New Jersey before heading out to sea will make a large difference for snowfall amounts from northern New Jersey into southern New England. The incoming system’s influence will likely reduce prospects of the storm’s stalling for a time, something that had been seen on some of the earlier guidance.
The worst-case scenario is that the storm would depart after reaching the vicinity of the Outer Banks. Under such a scenario, 6” snowfall amounts would likely be limited to a line running roughly from Trenton to Asbury Park in New Jersey and southward. Several inches of snow could still fall 50-75 miles north of that line, but little or nothing 100-125 miles north of it on account of the persistent confluence.
At this time, I’m assuming a sort of middle ground scenario in which the storm moves offshore somewhere between Salisbury and Ocean City and then heads eastward out to sea. I also favor the ECMWF’s colder thermal profile given its superior resolution, but could still envision some temporary precipitation-type issues along the New Jersey Shore, Delmarva, Long Island, and even into NYC and its nearby suburbs.
Considering these assumptions, my initial thinking for accumulations is as follows:
Baltimore: 18”-24”
Boston: 1”-2”
New York City: 6”-10”
Newark: 6”-12”
Philadelphia” 12”-18”
Sterling: 20”-30”
Richmond: 6”-10”
Washington, DC: 20”-30”
White Plains: 4”-8”
***********************************************************************************************************************************************
Posted 20 January 2016 – 9:00 AM
Some early thoughts on the January 22-24 Snowstorm…
So far, most of the guidance, excepting yesterday’s 12z run of the ECMWF, which was an outlier, indicates that the upcoming snowstorm could bring 10” or more snow to Washington, DC to New York City. Since 1950, only three January snowstorms have brought 10” or more snow to Washington, DC, Philadelphia, and New York City, including the one that was underway today in 1978.
At this point in time, the consistency of the guidance, including yesterday’s 12z ECMWF run, strongly suggests that the Baltimore to Washington, DC region could experience one of its five biggest snowstorms on record since at least the late 19th century. If the guidance holds, that region could be facing a 20”-30” snowfall. It’s too soon to reach firm conclusions right now, as details concerning the storm remain to be worked out, but that’s where the guidance has been over the past 48 hours.
My initial thinking is below:
The five biggest snowstorms on record for Baltimore and Washington, DC are below:
This storm is likely to reach blizzard proportions along parts of the East Coast. Moreover, the combination of a full moon and very high onshore winds could create significant coastal flooding and beach erosion. Such an impact will be a notable aspect of this storm aside from its prolific snows in parts of the Middle Atlantic region.
***********************************************************************************************************************************************
Posted 19 January 2016 – 2:21 PM
Snowstorm Possible for Parts of the East Friday into Sunday…
If one examines the data for January snowstorms going back to 1950, there have been 17 cases in which a storm brought 10” or more snow to one of the following cities: Boston, New York City, Philadelphia, Washington, DC. However, there are just 3 cases during which the storm brought 10” or more snow to at least 3 of those cities (January 1978, January 1996, and January 2005) and just one case in which all four of those cities received 10” or more snow (January 1996).
The 1950-2015 data is below:
With respect to the just-concluded and ugly 12z ECMWF run, I believe it’s too soon to write off the potential storm, particularly in the northern Middle Atlantic region and southern England areas. The continued continuity of the other guidance suggests that the upcoming storm may still bring 10” or more snow to 3 or even all 4 of those cities. Moreover, that such a storm is forecast to occur during an AO-/PNA+ synoptic pattern is consistent with January cases during an El Niño event for the January 23 +/- 15 day period.
Taking into consideration all of the ECMWF and GFS runs from 1/18 12z through 1/19 12z (3 runs of the ECMWF and 5 runs of the GFS), with greater weight applied to more recent runs, it appears that Baltimore and Washington, DC could experience a potentially major to historic snowfall event where both cities could approach or exceed 20” snowfall.
Finally, the 12z ECMWF dramatically cut back the QPF for such cities as New York and Boston from its 0z run, but it remains to be seen whether this big change is reasonable, especially as the GFS and GFS ensembles retained good run-to-run continuity.
Nevertheless, various scenarios are incorporated for the weighted model data, so a look what might be a worst-case may be useful. For purposes of comparison, I’ve provided the lowest QPF output from the ECMWF or GFS for the timeframe noted above, as well as the lowest QPF for any of the scenarios that were applied to the weighted series of model runs (e.g. 3σ below the weighted average figure from the model runs). Of course, we’re still fairly far out from the event, so a lot of uncertainty remains.
The 12z EPS and then 18Z GFS could provide early insight into the possible validity of the 12z ECMWF run.
***********************************************************************************************************************************************
Posted 15 January 2016 – 3:06 PM
The ECMWF Ensembles are forecasting that the MJO will likely predominate in Phases 2 and 3 through much of the rest of the second half of January. The forecast 500 mb pattern on the GFS ensembles for 240 hours and even farther out to 360 hours bears some similarities and also some differences from the composite MJO pattern for strong El Niño events (1/15-2/15 timeframe).
Note: All GEFS maps are from Tropicaltidbits.com
***********************************************************************************************************************************************
Posted 15 January 2016 – 9:43 AM
With today being day 46 of meteorological winter, we have now moved past the midpoint of the winter season. Of course, winter weather can occur in March and sometimes April. So far, the highlights have been:
- An historically warm December
- A massive flood along the Mississippi and Missouri Rivers
- A late-November snowstorm in the Midwest
- A blizzard that moved out of New Mexico and Texas
- A lack of snowfall in the East (To date: Albany: 4.3”; Baltimore: Trace; Boston: 1.2”; New York City: Trace; Philadelphia: Trace; Providence: 0.9”; Richmond: None; Washington, DC: Trace)
Until January, the predominant synoptic pattern featured an AO+/PNA+ combination. Since January, an AO-/PNA+ has taken hold. The AO has been negative for 14 consecutive days and at or below -3.000 for a week. That has tempered the warm anomalies in the East and contributed to some snowfall in New England.
Overall, the AO has averaged +0.133 for meteorological winter to date. It has been positive on 61% of days. However, it has been at -3.000 or below on 15% of days vs. +3.000 on 7% of days. The positive AO anomaly will very likely be wiped out by Sunday.
Right now, given the strong blocking that developed, it remains more likely than not that February will feature blocking, as well. Were the AO to fall to -4.000 or below in coming days (and some of the guidance still takes it there this weekend), that probability would increase.
In the meantime, the super El Niño continues to fade slowly. A gradual fade is likely to continue over coming weeks and perhaps pick up a little. Typically, such a development, especially with a basin-wide rather than East-based El Niño should favor more opportunities for cold in a large part of North America. However, the picture going ahead is less certain than usual.
What happens may well be highly dependent on the MJO. To date, winter 2015-16 has featured an abnormally strong MJO signal for super El Niño cases. This outcome may, at least in part, be the result of the widespread warm SSTAs in the Pacific.
If the past two super El Niño cases are representative, the amplitude should be somewhat lower during the remainder of meteorological winter. However, a sharp decline would not be likely. Therefore, one may cautiously expect a continued stronger than usual MJO signal and depending on the Phase, that signal could counter or even override the blocking (perhaps leading more to normal temperature departures than cold ones if unfavorable MJO Phases coincide with the blocking).
Finally, the long-range ECMWF guidance appears favorable for cold in the eastern part of the CONUS. However, if one takes the GFS MOS projections through January 20 and the actual temperatures from 1/1-14, it now appears that the CFSv2 may wind up with the better January temperature forecast for that section of North America than either the ECMWF or JMA, as warm anomalies now appear to be more likely than not for the monthly period in such cities as Philadelphia, New York, and Boston, even considering next week’s possible Arctic shot. Furthermore, the PNA+ will likely lead to warm anomalies developing in the Pacific Northwest near January 20 and that warmth could trim or even erase the cold anomalies that have accumulated to date there.
In contrast to the other guidance, the CFSv2, which is still outside its skillful range, is featuring more widespread warm anomalies. Right now, that does not appear to be the most likely scenario when one considers ENSO climatology, the location of best ENSO forcing during the current event, and potential for a blocky February, but it is a plausible one that cannot be dismissed. Should the MJO move into predominantly unfavorable phases and/or the SOI remains near neutral or positive for large parts of February, the warmer CFSv2 idea could prevail. It’s still too soon to embrace such a prospect, but that prospect cannot be ruled out.
Across much of Canada and the Pacific Northwest, warm anomalies could prevail in February courtesy of the PNA+. With a strong PDO+ persisting (December’s value was +1.01, an increase from November’s +0.86), a PNA+ is likely to predominate. The southern tier running from southern California to the Southeast could be on the cooler side of normal on account of an active subtropical jet. North of there, especially from the Plains States to the Middle Atlantic and New England regions is uncertain right now. Blocking would argue for colder outcomes in parts of that area, but a high-amplitude MJO in unfavorable phases (a risk not certainty) would argue against that outcome.
***********************************************************************************************************************************************
Posted 14 January 2016 – 9:14 PM
In #185 yesterday, I noted that some of the guidance was indicating that the SOI could go positive or even strongly positive down the road and posted the 500 mb pattern that has often prevailed during such cases with strong El Niños.
The 18z GFS ensembles have centered above normal height anomalies very close to the predominant position in December.
***********************************************************************************************************************************************
Posted 14 January 2016 – 10:20 AM
Alex became a hurricane this morning. It’s the first hurricane in the Atlantic basin in January since Alice (which formed in December 1954) and the first to develop in January in the Atlantic basin since 1938.
From the NHC:
000
WTNT41 KNHC 141434
TCDAT1
HURRICANE ALEX DISCUSSION NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL AL012016
1100 AM AST THU JAN 14 2016
Remarkably, Alex has undergone the transformation into a hurricane.
A distinct eye is present, embedded within a fairly symmetric mass
of deep convection. Water vapor imagery shows that the upper-level
trough is now west of the cyclone, with divergent flow over the
center - indicative of a tropical transition. It is very unusual to
have a hurricane over waters that are near 20 deg C, but the
upper-tropospheric temperatures are estimated to be around -60 deg
C, which is significantly colder than the tropical mean. The
resulting instability is likely the main factor contributing to the
tropical transition and intensification of Alex. With these
changes, the government of the Azores has issued warnings for most
of the Azores islands.
The initial intensity is set to 75 kt in accordance with the
analyzed Dvorak T-number of 4.5. Only slight additional
intensification seems possible since the system will be passing
over even colder waters during the next day or two. In 36 hours,
the global models suggest that the cyclone will become
extratropical as it begins to merge with a large low pressure area
at high latitude. The post-tropical cyclone is then likely to lose
its identity after 48 hours.
The initial motion is north-northeastward or 020/17 kt. Alex is
being steered by a shortwave mid-level trough that is rotating
around a larger trough to the northwest. This should cause the
cyclone to turn northward and north-northwestward and accelerate
over the next couple of days. The official track forecast is very
similar to the previous one and also quite close to the consensus
of the tightly-packed dynamical model forecast tracks.
Alex is the first hurricane to form in the month of January since
1938, and the first hurricane to occur in this month since Alice of
1955.
FORECAST POSITIONS AND MAX WINDS
INIT 14/1500Z 31.5N 28.4W 75 KT 85 MPH
12H 15/0000Z 34.3N 27.7W 80 KT 90 MPH
24H 15/1200Z 38.9N 27.7W 75 KT 85 MPH
36H 16/0000Z 45.3N 28.6W 60 KT 70 MPH...POST-TROP/EXTRATROP
48H 16/1200Z 53.0N 31.5W 60 KT 70 MPH...POST-TROP/EXTRATROP
72H 17/1200Z...DISSIPATED
$$
Forecaster Pasch
***********************************************************************************************************************************************
Posted 13 January 2016 – 9:28 AM
Over the past 5 days, a very stable AO-/PNA+ pattern has prevailed. During that time, the AO has ranged from -3.608 to -3.399 and the PNA has ranged from +0.736 to +1.014. During that time, a clipper system streaked across the Northern Tier and bombed out in the Gulf of Maine bringing up to 10” of snow to parts of Maine and lesser amounts from Pennsylvania across southern New York State (excluding New York City and its immediate suburbs) and southern New England. In short, those snow-starved cities had a “near miss.” However, there are no consolation prizes.
Over the next 5-7 days, another storm will head to the Great Lakes region while a strong secondary system moves north-northeastward along the East Coast. The primary system will be sufficiently strong (<995 mb) that it will drive a lot of warmer air northward, once more depriving snow-starved cities such as New York, Philadelphia, and Washington of a meaningful snowfall. In its wake, Arctic air should again knock down temperatures from the Plains States to the East Coast.
However, if one looks out to the Pacific, some of the guidance is suggesting that the SOI will rebound to positive and possibly strongly positive values within 10 days. During strong or super El Niño events, that development can coincide with the development of strong ridging over some part of Ontario or Quebec.
The ECMWF ensembles and GFS ensembles are in agreement about the development of just such ridging during the 240-hour to 288-hour timeframe. If that occurs, what should have been the locking in of a colder pattern on account of the blocking—something I had expected—could wind up being a more variable pattern with shots of cold alternating with warmer conditions from the Plains States to the East. The Middle Atlantic region, New England, and Quebec might have the highest probability of seeing net warm anomalies in the extended range if such a pattern develops. This issue will need to be revisited in coming days.
Finally, on the stratospheric front, a strong Wave 2 pulse is likely to develop over the next 10-15 days. However, it’s far too soon to be sure whether the wave will have the amplitude necessary to trigger a sudden stratospheric warming event. The ECMWF argues against such an event through the next 10 days, but 10 days is beyond a reasonably accurate forecasting horizon. Such events are only forecast with reasonable accuracy within a few days of their onset, so aside from noting the forecast development of the wave, more data will be needed to reach any conclusions about the likelihood of such an event. The infrequency of such events—about one every two winters—argues for holding off on conclusions until more data is available.
***********************************************************************************************************************************************
Posted 11 January 2016 – 11:18 AM
In Fyodor Dostoevsky’s Crime and Punishment, Dostoevsky wrote of Rodion Raskolnikov, who conceived and carried out a plan to murder a pawnbroker for her money, “At times he was a prey to agonies of morbid uneasiness, amounting sometimes to panic.” Such sentiments seem to arise from time to time when the meteorological outcomes and evolving operational model/ensemble forecasts seem not to fulfill the potential of a promising pattern. They seem especially prevalent following long periods of unseasonable warmth. In the wake of a searing December that left dreams of cold and snow in charred ruins and a transitional period in January that has trimmed but not eliminated warm anomalies in parts of North America that had experienced December’s historic warmth, such sentiments appear widespread as the operational models continue to struggle on the synoptic details related to a potential storm for the January 16-18 timeframe. That some of the guidance has shifted from snowy or out-to-sea solutions to a cutting system have exacerbated such concerns.
At the same time, the latest guidance no longer shows quite as extreme a blocking situation as suggested earlier. Rather than forecasting the AO to bottom out at or below -5.000, the latest run of the GFS ensembles shows the AO reaching a minimum near -4.000.
Should those in the East simply assume a “rule” by which forecast warm anomalies will verify, cold ones won’t, rainy solutions will, snowy solutions won’t? In other words, should we write off Winter 2015-16 as a failure now that we’re approaching the mid-point of meteorological winter?
Even with the reduced magnitude of blocking, not to mention El Niño climatology, doing so would be perilous. Although there are no guarantees of a very snowy outcome similar to winter 1957-58, a notable scarcity of snowfall along the lines of 1997-98 also appears unlikely.
At the same time, the PNA+ will likely lead to a warming in the West. Nevertheless, it does appear likely that parts of the drought-stricken region will continue to experience opportunities for beneficial rains.
Below are some charts related to less extreme blocks that occurred in the January 15 +/- 10-day range related to February.
***********************************************************************************************************************************************
Posted 8 January 2016 – 11:30 AM
With the Arctic Oscillation’s beginning its descent toward forecast values of -4.000 or below over the next 4-7 days, opportunities for measurable snowfall should increase over parts of North America, particularly the Middle Atlantic region. Since 1950, there have been 10 cases during which the AO first fell to -4.000 or below during the period from January 15 +/- 10 days. With two exceptions, Boston, Detroit, New York City, Philadelphia, and Washington, DC all saw at least some measurable snowfall from the date the AO first fell to -4.000 through the following 30 days.
Below is the latest AO forecast and statistics for those cases:
***********************************************************************************************************************************************
Posted 8 January 2016 – 9:15 AM
Small changes in the Teleconnection Forecasts…
– There is larger agreement among the GFS ensemble members that the AO will fall to -5.000 to -4.000 toward mid-month, with somewhat fewer taking it below -5.000. The overall idea of the development of severe blocking remains unchanged. Today’s AO figure was -2.758, which is the lowest it has been this winter.
– The NAO was slightly negative. It has been positive for 37 of the first 39 days of meteorological winter or 95% of the time. In contrast, the AO has been positive 72% of the time so far. The NAO is forecast to go strongly negative.
– The PNA remains positive. Consistent with a PDO+, the PNA+ has been the general rule this winter so far. The PNA has been positive for 82% of days and at or above +1.000 on 38% of the days. It is forecast to remain positive through the extended range, though one cluster of ensembles takes it to strongly positive levels and another cluster toward near neutral levels by the end of the ensemble forecast.
All said, given climatology, the forecast sustained AO-/PNA+ pattern should lead to an increase in snowfall opportunities in the eastern U.S., with the largest increase over the baseline being focused on the Middle Atlantic region.
***********************************************************************************************************************************************
Posted 7 January 2016 – 10:51 AM
More thoughts on the January AO…
Yesterday, in message #158 (https://www.americanw…sion/?p=3832891), I highlighted the GFS ensembles’ forecast of an extremely negative Arctic Oscillation (AO). There was widespread agreement that the AO would fall below -4.000 and perhaps -5.000 toward mid-January. The post included data concerning a recent increase in extreme cases since 2000 relative to the historic 1950-2015 period.
The updated GFS ensemble forecast is little changed from yesterday’s.
This post takes a closer look at January’s Arctic Oscillation. Since 1979, the 30-year moving average of the monthly standard deviation has increased nearly 8%. If one looks closer at the data, the January cases beginning in the early 2000s accounts for this increase in variability.
What this means is that the AO has recently become more variable in January. Some of that variability may be contributing to the increase in extreme daily values.
The variability is likely a function of stratospheric developments and sea-ice-atmosphere coupling, and related interactions. Since the 1970s, the RATPAC dataset has revealed a cooling trend at 30 mb. Stratospheric cooling should, in general, favor a stronger stratospheric polar vortex and perhaps greater stability in the AO. Some of this tendency toward higher AO values should be reflected in the AO index.
Looking at January, the AO was +3.000 or above on 4.6% of dates in the 1950-2015 period. However, since 2000, it has reached +3.000 or above on 6.5% of dates. On the negative side, the AO has been -3.000 or below on 10.3% of dates during the 1950-2015 period. However, since 2000, it has been at or below -3.000 on 7.1% of dates in January. The respective figures for +4.000 or above are 1.5% and 1.2%, while those for -4.000 or below are 3.4% and 1.6%. This data shows that a strongly positive AO has become more frequent in January, but that rise has not translated into an increased frequency of +4.000 or greater values. At the same time, there has been a decreased frequency of strong January blocking (especially in the frequency of AO values of -4.000 or below). These outcomes appear to be reasonably consistent with what one would expect from a cooling stratosphere.
But then, there’s a curveball of sorts. Since 2000, there have been no January cases on which the AO reached +5.000 or above vs. the 1.0% figure for the entire 1950-2015 period. However, the frequency of extreme negative cases (-5.000 or below) has increased from 0.8% of all cases during the 1950-2015 period to 1.0% of cases during the 2000-2015 period. Sample size (all of the 2000-2015 cases occurred in 2010) may provide the explanation, but a return of -5.000 or below values as suggested by the GFS ensembles would call into question the sample size argument.
Since the extreme negative values are inconsistent with stratospheric cooling, it is plausible that the sea-ice-atmospheric relationship may provide the stronger explanation for that possible outcome. There has been a decline in average January Arctic sea ice extent since the 1980s and that trend may be contributing both to increased AO volatility and the possible uptick in extreme negative cases in January.
January Arctic sea ice extent during the 1990s was 3% lower than that for the 1980s. During the 2000s (2000-2015), average sea ice extent was 7% lower than it was during the 1980s. The last 10 years (2006-15), saw January’s average sea ice extent come out 10% lower than the 1980s average. Furthermore, the January standard deviation in Arctic sea ice extent has also declined somewhat. In sum, January Arctic sea ice extent has declined and has become slightly more stable on a day-to-day basis at those reduced levels.
For now, it’s too soon to be sure what mechanisms are at play. However, it is plausible that the decline in average January Arctic sea ice extent is more than compensating for a cooling stratosphere in driving an increase in AO variability in January. The question concerning the increase in extreme negative AO cases is less clear.
***********************************************************************************************************************************************
Posted 6 January 2016 – 11:27 AM
A closer look at the February outcomes following January cases when the AO fell to -5.000 or below:
***********************************************************************************************************************************************
Posted 6 January 2016 – 10:17 AM
Extreme Blocking Forecast…
To date, the Arctic Oscillation (AO) has averaged +0.973 during the 2015-16 meteorological winter. 76% of days have seen the AO positive and 59% of days have seen the AO at or above +1.000. On 8% of days, the AO has been +3.000 or above. Its highest value has been +4.503, which was reached on December 22, 2015. The AO has been negative on 24% of days and at -1.000 or below on 16% of days. Its lowest value so far is -2.299, which was reached on January 5, 2016.
However, the latest GFS ensembles are forecast the AO to plunge. There is strong agreement among the ensemble members that the AO will fall to -5.000 or below.
Such extreme values are uncommon. However, such extreme values have become somewhat more common since 2000.
Such extreme blocking would suggest troughing in eastern North America. More importantly, should such extreme blocking develop, it would provide a strong signal of a blocky February. In short, even as the most recent December proved to be an autumn, not winter month, an extreme AO-, should it develop, could offer the strongest signal so far that there will be plenty of opportunity for winter weather from mid-January onward. North America and Europe would both see such opportunities if past extreme January blocking cases are representative.
***********************************************************************************************************************************************
Posted 5 January 2016 – 10:41 PM
This morning the Arctic Oscillation was -2.299. This is the lowest figure so far this meteorological winter. To date, the AO has averaged +1.063, however with blocking forecast to deepen in coming days and remain sustained through at least mid-month, that positive anomaly should shrink.
Even as the current block is only in its 4th day, the AO-/PNA+ combination led to a discharge of Arctic air from northern Canada into the eastern United States. This morning’s low temperatures included:
Albany: 2°
Boston: 8°
Burlington: 2°
Caribou: -9°
Detroit: 12°
Montreal: -6° (-21°C)
New York City: 11°
Philadelphia: 12°
Richmond: 16°
Toronto: 5° (-15°C)
Washington, DC: 16°
Although this cold shot will prove transient as warmer air sweeps back into the East, it was sufficient to send monthly anomalies below normal in such cities as New York for the first time since early October.
Should the blocking be sustained as is forecast, a more sustained period of cold will likely set in from the Plains States eastward near mid-month give or take a few days. The trimmed pool of objective analogs from the GFS ensembles suggest that odds favor at least the 15th through the 20th as being cooler than normal in the eastern third of the CONUS.
Toward mid-month, the PNA+ will likely result in the West’s experiencing the development of a sustained period of above normal temperatures.
Beyond the 20th, there remains a lot of uncertainty. Some of the guidance looks to relax the blocking resulting in the development of a milder regime. However, even on the ensembles, forecasting skill that far out is fairly low, so it is not assured that blocking will relax. Should blocking persist, the cold could do so, as well.
It should be noted that major long wave patterns have proved fairly persistent since at least the fall. If that tendency holds up, the current AO-/PNA+ dual blocking regime could hold or any break in the blocking could be temporary. The 1966 and 1978 objective analogs that are in the mix provide some credence to that possible scenario.
************************************************************************************************************************************************
Posted 3 January 2016 – 9:11 PM
This morning saw the AO at -1.556 and the PNA at +1.785. The EPO was also negative. This EPO-/AO-/PNA+ combination is the opposite of what prevailed during much of December. It is yet another indication that the predominant December pattern has broken.
A downstream response to such a pattern should begin to yield colder outbreaks over a larger part of North America than has been the case so far and eventually the development of a trough in parts of the East. Once that happens (probably near mid-month +/- a few days), the pattern could favor sustained cold. There could also be increased opportunities for snowfall, but we’re not yet there.
Following the early week cold shot, moderation will take place. Readings will return to above normal values in a large part of North America that just went through December’s historic warmth. But that period of moderation will likely be temporary given the current and forecast state of the teleconnections.
************************************************************************************************************************************************
Posted 1 January 2016 – 3:09 PM
December will go down in the record books as an historically warm month. Some average monthly temperatures and temperature departures from select cities:
Back on December 17, the GFS ensembles suddenly indicated that a PNA+ could return. Since then, one has witnessed verification of that forecast and the SOI’s having gone strongly negative. Moreover, the ensembles indicate a sustained period of blocking should develop over the next few days.
The upcoming cold shot that will slide eastward in coming days will be fairly sharp. It will serve a reminder that even as December as been lost to an ocean of warmth, winter has not been vanquished. Parts of the Western U.S. already have experienced winter’s fury in the form of a blizzard that paralyzed parts of New Mexico and Texas.
That cold shot will very likely yield to moderation with some above normal readings. However, the warmth won’t even begin to approach the levels that had been so common in December. Instead, the pattern will continue to evolve. Near mid-month, give or take a few days, the sustained blocking may well lead to sustained cold.
Finally, cities such as Washington and New York, among others, could see increased opportunities for snowfall should the AO-/PNA+ pattern persist. For example, the percentage of days receiving measurable snowfall in New York is 9% above the January average (1950-2015) during such patterns. In Washington, DC, the percentage of such days is nearly 22% above the January average.
In sum, the transitional period remains underway. A sustained cold pattern could develop toward mid-month and, opportunities for snowfall could begin to increase ahead of that colder pattern.
************************************************************************************************************************************************
Posted 31 December 2015 – 9:37 AM
No changes in thoughts this morning…
1. The AO is now poised to dive strongly negative over the next 7 days according to the GFS ensembles.
2. The EPO is forecast to have a sustained period of negative values for the first time since November 20-30.
3. The PNA remains positive.
4. 500 mb height anomalies have been evolving away from the predominant December pattern.
In short, North America is in the midst of a pattern evolution and this transitional state may last 1-2 weeks. If blocking is sustained afterward, sharper and more expansive outbreaks of cold could occur.
Not surprisingly, the CFSv2 adjusted its warm anomalies northward overnight.
************************************************************************************************************************************************
Posted 30 December 2015 – 9:15 AM
This morning, the SOI had fallen to -27.30. That is its lowest figure since December 4. At the same time, the PNA remained positive and the ensembles remained in agreement that the AO will very likely go negative over the next week. In short, a pattern evolution remains underway.
However, if one looked at the latest CFSv2 forecast, one finds warm anomalies forecast across much of North America with the exception of the southern portion of the United States and Mexico. One also finds an expansive area of much below normal precipitation forecast for the Ohio and Tennessee Valley regions.
Such an outcome would not be unprecedented. In fact, it is remarkably similar to the outcome for January 1983, though much warmer across northern Canada and Alaska and with more expansive warmth in the CONUS.
With that model now in its skillful range, is there any hope for colder outcome? A comparison of the 1983 teleconnection indices and ensemble forecast may provide some insight.
In January 1983, the PNA averaged +1.18. Moreover, the PNA was positive on 28 out of 31 days. The latest ensemble guidance forecasts a PNA+ and the current PDO+ also favors such an outcome.
When it comes to the AO, January 1983 had an AO average of +1.359. 22 out of 31 days saw the AO positive. A short period of blocking occurred during the January 16-23 timeframe when the AO was negative for 6 out of 8 days. A long-duration period of blocking developed on January 29.
In contrast, the current ensemble forecast shows the AO going negative early in January and remaining there through at least mid-month. That’s a significant difference from what happened in 1983.
All said, assuming the blocking develops and is sustained, my thinking remains that the warmth will be less expansive than what is shown on the latest run of the CFSv2. For a rough idea of my thinking, one can expand the areas of cool anomalies, anomalies <0.5°C above normal, and anomalies less than 1°C above normal northward by about 5° latitude.
If, however, the blocking proves transient and the polar vortex rebuilds for the second half of January, then the warmer CFSv2 idea might well have merit. Right now, I think that’s not a high probability outcome, but there is sufficient uncertainty in ensemble forecasting skill related to the AO to make it impossible to completely rule it out.
In sum, a pattern evolution away from the predominant December pattern is underway. A 1-2 week transitional period lies ahead. Afterward, especially if blocking is sustained, the potential for increasing cold shots with greater geographic coverage exists. The second half of January would wind up colder relative to normal than the first half of January in much of the CONUS and parts of Canada. That’s my baseline thinking as December nears an end.
************************************************************************************************************************************************
Posted 29 December 2015 – 9:08 AM
This morning, the Arctic Oscillation (AO) was +0.805 vs. +4.485 a week ago. The PNA was +1.351 vs. -0.261 a week ago. The latest guidance is in strong agreement that an AO-/PNA+ (and EPO-) pattern is likely to develop early in January. Should that pattern be sustained, it would favor a more expansive area of cold anomalies in North America than has been the case so far this winter. For illustrative purposes, below are composite 500 mb and temperature anomaly maps for January cases when the monthly AO average is -1.000 or below, monthly PNA average is +1.00 or above, and when the AO monthly average is -1.000 or below and the PNA monthly average is +1.00 or above.
Right now, it’s too soon to be sure that the January averages will reach such magnitudes, but the maps are useful in illustrating the growing probability that cold anomalies will be more expansive than they were in December. It remains plausible given the super El Niño that much of Canada would wind up warmer than normal and the northern tier of the U.S. from Montana or North Dakota eastward into northern New England (possibly somewhat south or north of that line) would see monthly temperatures average on the warm side of normal. Some blend of the composite for PNA anomalies of +1.00 or above, January 1878 (message #118), and January 1983 (message #118) might be reasonable barring a January AO average of perhaps -2.000 or below.
************************************************************************************************************************************************
Posted 28 December 2015 – 9:01 AM
Long-Awaited Pattern Evolution Now Underway…
The long-awaited pattern regime change from a persistent super ridge centered over eastern North America is now underway. The SOI has now fallen to -23.25 after peaking at +30.72 on December 24. The rate of decline in the ongoing super El Niño has shown some indications of picking up. The most recent weekly changes were as follows:
Region 1+2: -0.3°C
Region 3: -0.2°C
Region 3.4: -0.2°C
Region 4: -0.1°C
In the larger scale, the kind of historic warmth that covered the eastern half of December during super El Niño events is typically unsustainable, not just in magnitude (otherwise that kind of warmth wouldn’t be such a rare event), but also in coverage. Even as the sample size is limited to two super El Niño cases (1877-78 and 1982-83), super warm winters for the entire December-February period are rare. Hence, with a degree of caution, one can argue that it is more likely than not that the warm anomalies should be expected to retreat to the northern tier (perhaps running from Montana or North Dakota to northern New England and northward) if the current ENSO event is reasonably similar to the two cases and the larger historical experience has relevance. The latest CFSv2 guidance shows just such an outcome.
The ensembles have persistently been forecasting a return of the PNA+, which is a favored state when the Pacific Decadal Oscillation is positive. More recently, ensemble support for AO- and EPO- blocks has increased. The 12/28/2015 GFS ensembles now show strong agreement that the AO will be falling to negative values with a cluster of members supporting severely negative values during and after the first week in January. Even a few ensemble members support a negative NAO during the extended range.
At this point, the guidance strongly supports the idea that a pattern evolution is now underway. There will likely be a short lag before the impact of the blocking takes hold on the hemispheric pattern. Before then, there will likely be a transitional pattern that lasts 1-2 weeks. During that transitional pattern, eastern North America will likely be much cooler than during December, even as readings average somewhat above normal in some of the areas that saw extraordinary warmth during December. There may yet be opportunities for systems to cut to the Great Lakes, producing short periods of much warmer than normal readings in the East. The West will generally remain colder than normal, but toward the end of the transitional period, a warming trend may begin to appear in the Pacific Northwest and northwestern Canada on account of the PNA+.
What happens afterward will depend on whether the forecast blocking develops. The turnaround that occurred during winter 1965-66 when sustained blocking developed in late January could provide some insight.
************************************************************************************************************************************************
Posted 25 December 2015 – 9:17 AM
Did Santa deliver an AO- forecast?
That seems to be a reasonable question, even as record high temperatures have again tumbled in parts of the East. The latest GFS ensemble forecast shows the development of an AO-/PNA+ pattern.
************************************************************************************************************************************************
Posted 24 December 2015 – 1:42 PM
Latest 11-15-day 500 mb anomalies (12z GFS ensembles):
************************************************************************************************************************************************
Posted 24 December 2015 – 9:44 AM
The SOI was up to +30.72 this morning. That’s its highest figure since June 13, 2014 when it reached +31.28. This lofty value coincides with an extreme pattern amplification that is currently underway and responsible for record warmth in the East.
All of the guidance continues to suggest that decay of the current pattern, which should allow the first week of January to start out with more seasonable temperatures in a large part of the CONUS. The westward location of the Aleutian Low and PNA+ will result in the ridge’s being centered in western North America, not eastern North America as has been the case for much of December.
************************************************************************************************************************************************
Posted 23 December 2015 – 10:36 AM
If one examines the latest monthly forecast from the CFSv2 for January, one might be tempted to believe that the traces of summer than have lingered throughout December to date might never be purged fully from North America. Yet, there continue to be increasing hints of a changing pattern.
1. The PNA is forecast to go positive.
2. Even as there remains poor run-to-run continuity regarding the EPO and disagreement among the guidance, it does appear that the EPO will at least go neutral in the extended range.
Both those developments should be sufficient to relax the predominant pattern responsible for December’s abnormal warmth.
If one looks further at the GFS ensemble trimmed objective analog pool, taking into consideration, ENSO, one finds that the cases rolled forward for January would yield a different pattern. The northern tier of the CONUS would remain generally warmer than normal, as would much of Canada. However, there would also be a large area of near normal anomalies, as well.
Furthermore, the 11-15 day mean 500 mb pattern seems to offer a hint of the predominant pattern suggested by the latest GFS ensemble objective analog pool rolled forward for January.
At this point, even as one should not take the numbers literally (e.g., warm anomalies may be more widespread, though they won’t rival December’s extreme figures) and should be aware that there remains uncertainty, the idea that January will not be a replica of December appears to have reasonable support, even if the CFSv2 remains locked on a much warmer idea.
************************************************************************************************************************************************
Posted 22 December 2015 – 08:37 AM
More hints of at least a pattern relaxation…
If one looks at the latest run of the GFS ensembles, one finds more evidence that ridging is forecast to develop in the West and the pattern responsible for the extreme warmth in the eastern half of North America is poised to relax.
Below are charts showing a comparison of the composite anomalies for extreme warmth during the second half of December and the 12/22/2015 0z run of the GFS ensembles at 48 hours.
Afterward, the 500 mb height anomalies for 240 hours and 360 hours are posted.
In sum, it now appears very likely that the pattern will relax in the extended range. The major question is whether the relaxation will prove temporary or a stage along the way toward a pattern change that will provide for more persistent cold across the section of North America that has experienced excessive warmth.
************************************************************************************************************************************************
Posted 21 December 2015 – 02:39 PM
During the past four weeks, there has been only a slight decay of the ongoing super El Niño. Below are the changes in anomalies for the ENSO regions for the week centered around December 16 vs. the week centered around November 18:
Region 1+2: +0.3°C
Region 3: -0.1°C
Region 3.4: -0.2°C
Region 4: -0.1°C
The average sea surface temperature in Region 4 has now been at or above 30.0°C for the last eight weekly periods. In coming weeks, some of the ENSO region cooling should pick up a little bit, but strong El Niño conditions appear likely to persist through much of January and perhaps February, as well.
However, as began to show up in the ensembles (Message #65), what had been a tentative signal for the return of a PNA+ pattern is now a more certain signal. As a result, one could begin to witness the development of some ridging in the West as 2016 approaches and arrives.
At the same time, some of the guidance suggests a potentially large drop in the SOI. Such an outcome during strong El Niño events has offen seen the development of a weak trough in the southeastern United States.
So all in all, it appears the that pattern responsible for what will likely be an historically warm December in parts of North America could yield to some relaxation. While the northern tier might well remain warmer than normal, the anomalies should be less excessive than they were in January. Cool shots could become somewhat more frequent and a little sharper.
In the West, where cool anomalies are likely for the closing 10 days of December, moderation will likely take place as January gets underway. It still remains to be seen whether this relaxation in the pattern will mark a longer-duration pattern change or a pause prior to the return of the predominant pattern that has provided for much above normal temperatures in large parts of North America during both November and December.
************************************************************************************************************************************************
Posted 20 December 2015 – 09:36 AM
Hints of Change?
If one examines the 8-day and 11-day GFS ensembles, one finds that 50% of the ensemble years from the 8-day pool are replaced in the 11-day pool. This lack of consistency can occur ahead of evolving pattern changes.
If one proceeds to look at the trimmed pool of common objective analog cases, on finds four winters: 1954-55, 1974-75, 2006-07, and 2007-08. The area of December warmth from that pool is reasonably similar to the warmth that has covered North America to date, though it is of lesser magnitude. January also shows a fair degree of warmth, but less than that shown on the CFSv2.
However, if one looks more closely at the second half of January, 3 out of the 4 cases feature widespread cold anomalies.
Whether or not the pattern will, in fact, change toward one that favors a lot more cold at some point during the second half of January remains to be seen. But at least some of the guidance provides a measure of possible support for that outcome.
************************************************************************************************************************************************
Posted 18 December 2015 – 07:45 PM
Buffalo has now had its first measurable snowfall of the season. From the NWS in Buffalo:
NWS BUFFALO @NWSBUFFALO 27m27 minutes ago
Buffalo airport records its first measurable snow of the season. https://ow.ly/i/flCjs
************************************************************************************************************************************************
Posted 18 December 2015 – 09:35 AM
After spending five days below 0 and having fallen as far as -1.084, the Arctic Oscillation (AO) returned to positive values today (+0.644). So far, the AO is averaging +0.828 this month and has been positive on 72% of the days.
The latest ensemble guidance shows the AO returning to strongly positive values in coming days and likely to remain predominantly positive to strongly positive the remainder of December and into the first days of January.
Given the AO forecast, a monthly average of +1.000 or above appears likely. However, even if the AO forecast proves accurate, that does not automatically mean that a scenario similar to 1988-89 that saw the AO remain predominantly positive to strongly positive throughout January and February is assured.
At least two big AO regime changes occurred followed the AO’s rebounding to strongly positive values at the end of December. On December 31, 2004, the AO rose to +3.133 and averaged +3.532 during the January 1-10, 2005 period. On December 30, 2006, the AO reached +3.640 and averaged +3.604 for the January 1-10 period and +3.342 for the January 1-5 timeframe.
Both winters saw blocking develop during the second half of January and blocking throughout much of February. On January 21, 2005, the AO went negative and was predominantly negative to strongly negative through March. On January 21, 2007, a short period of blocking developed. Sustained blocking took hold on February 1 and lasted through February 26.
Of course, during the nightmare of 1988-89, the AO fell below 0 on just 1 day (-0.318 on March 4, 1989) out of the 104-day period running from January 1, 1989 through April 14, 1989. Even then, much of the CONUS saw colder-to-much colder than normal temperatures during February 1989.
In short, two points are important:
- The return of strongly positive AO values does not mean that blocking must largely be written off this winter.
- Even if the AO+ predominates, other aspects of the pattern can still allow for wintry weather during parts of January and/or February.
************************************************************************************************************************************************
Posted 17 December 2015 – 10:50 AM
The Return of the PNA+?
Across much of North America, when one steps outside, one finds December 2015 lies in charred ruins. Where there should be a blanket of freshly fallen snow, one finds, barren ground, green grass, and even occasional buds and blossoms. In cities where the thermometer should routinely drop to freezing or below, getting there is a seemingly hopeless ordeal. In place of a typically biting North wind, balmy breezes have largely vanquished the concept of wind chill.
Just beyond the first half of December, much of North America has been covered by an ocean of warmth. If one looks at the latest CFSv2 idea for January, that model expects more of the same.
If one looks at the latest objective analogs from the GFS ensembles, one finds 1988-89 and 2001-02 in the mix (20% of the 8-day and 11-day analogs).
Nevertheless, that does not mean that December’s warmth will roll on through the winter until the arrival of spring.
First, the CFSv2 is still outside its skillful range for its month ahead forecast.
Second, since 1870, there were three prior El Niño cases that saw overwhelming coverage of December warmth similar to what has been the case so far this month: 1877-78, 1941-42, and 1957-58. 1877-78 saw some relaxation of the warmth in January. 1941-42 and 1957-58 featured a much larger turnaround.
Third, the same pool of objective analogs includes the turnaround winters of 1957-58 and 2006-07. In fact, those winters account for 30% of the analogs.
Fourth, the latest GFS ensemble guidance suggests the possibility of a return to PNA+ values around December 27-28. In 1957-58 and 1965-66, the return of PNA+ values coincided closely to the return of Arctic Oscillation blocking.
For now, relentless waves of warmth continue to roll across North America, one after another. Nevertheless there are some hints of possible future change. Within 6-8 days, a more sustained period of colder weather is likely to overspread western Canada and the western United States. Whether one witnesses the birth of a trough in the East will depend on how the pattern evolves from there. A return of the PNA+, if it occurs, could facilitate that process.
Should such a scenario play out, the next question would be whether winter would make a temporary stay over a small part of the Continent (as happened in 1877-78) or a much more sustained and widespread stay as happened in 1941-42 and 1957-58.
************************************************************************************************************************************************
Posted 16 December 2015 – 10:41 AM
The journey through Winter 2015-16 has now passed the mid-point of December. Much of North America has wandered horribly off course. Did North America lose its seasonal maps or GPS?
Rather than encountering the rising Arctic blasts and periodic blankets of snow typical of deepening winter, much of North America has instead found itself locked into a seemingly endless inferno relative to seasonal norms. As of December 16, cities such as Chicago, Detroit, Minneapolis, New York, and St. Louis have accumulated monthly temperature anomalies of 10° or more above normal. New York City has already shattered its December record for the most days on which the minimum temperature has remained at 50° or above. Buffalo has yet to experience a measurable snowfall.
Put simply, a nightmare is unfolding. A hypothetical scenario for a record-breaking El Niño (https://www.americanw…31#entry3660754) suggested that such a nightmare was plausible. Both the latest CFSv2 forecast for January and the January outcome from that hypothetical scenario provide little relief for those in search of winter.
The latest trimmed objective analog pool from the GFS ensembles suggest that cities such as Boston, Chicago, Detroit, New York, Philadelphia, and St. Louis have a high to very high probability of experiencing a warmer than normal January 1.
Some may well be tempted to write off winter even before it has had a chance to exert its influence. Yet, even as such a nightmare scenario cannot fully be dismissed (especially with the ensembles pointing to a continuation of the EPO+/AO+/PNA- teleconnection combination through the remainder of December), there remain suggestions that this nightmare can pass.
First, a number of El Niños (1957-58, 1965-66, and 2006-07) featured a dramatic turnaround from seemingly endless fall to winter.
Second, among the GFS ensembles’ objective analogs are cases from those three “turnaround” winters.
Third, even as it has been dented, the PDO remains positive. That scenario favors a PNA+ pattern, so it remains more likely than not that the PNA- regime will eventually yield to the return of the PNA+.
In short, even as Canadian and American snow geese alike have been worn down by day-after-day of unrelenting waves of warmth, there remains a reasonable prospect that Winter 2015-16 will awaken. Before then, the days ahead could bring more misery of warmth and hunger for snowfall.
Finally, winter is not absent from the entire continent. Alaska has been experiencing noted cold. The western third of North America is likely to experience often cooler than normal weather with prospects of above normal snowfall through much of the second half of December. In fact, the same objective analog pool suggested that Seattle had an implied 57% probability that January 1 would wind up colder than normal. In short, winter has a toehold in parts of North America. So long as all the cold is not driven to the other side of the hemisphere, there remains hope for a change, especially when the “turnaround” El Niño cases are considered. Therefore, I am not ready to “cancel” winter even as the mercury rises yet again into the balmy 50s as I post these thoughts.
************************************************************************************************************************************************
Posted 15 December 2015 – 05:03 PM
Select record high temperatures (December 15, 2015):
Albany: 61° (tied record: 61°, 1901)
Allentown: 66° (tied record: 61°, 2008)
Bridgeport: 63° (old record: 59°, 1975)
Danbury: 65° (old record: 60°, 2008)
Islip: 62° (old record: 59°, 2008)
New Haven: 61° (old record: 60°, 1975)
New York City:
…Central Park: 68° (old record: 67°, 2008)
…JFK: 64° (old record: 61°, 2001)
Newark: 68° (old record: 67°, 2008)
Philadelphia: 69° (old record: 66°, 2008)
Pittsfield: 60° (tied record: 60°, 2008)
Poughkeepsie: 63° (tied record: 63°, 2008)
Providence: 64° (old record: 62°, 2008)
Trenton: 67° (old record: 66°, 2008)
Westhampton: 62° (old record: 59°, 2008)
White Plains: 62° (old record: 61°, 2008)
Wilmington, DE: 68° (tied record: 67°, 1971)
***********************************************************************************************************************************************************
Posted 14 December 2015 – 05:09 PM
Select daily record high temperatures for December 14, 2015:
Allentown: 68° (old record: 60°, 2001)
Atlantic City: 65° (tied record: 65°, 1929)
Baltimore: 71° (tied record: 71°, 1929)
Binghamton: 61° (old record: 55°, 2006)
Bridgeport: 60° (tied record: 58°, 1991)
Buffalo: 71° (old record: 64°, 1901)
Harrisburg: 66° (old record: 64°, 1927)
Islip: 62° (tied record: 58°, 1991)
New York City:
…Central Park: 67° (tied record: 67°, 1881)
…JFK: 60° (tied record: 60°, 2001)
…LGA: 64° (old record: 63°, 2001)
Newark: 67° (old record: 63°, 2001)
Norfolk: 77° (old record: 75°, 2001)
Philadelphia: 70° (old record: 69°, 1881)
Raleigh: 75° (old record: 74°, 1918)
Richmond: 72° (old record: 71°, 2001)
Rochester: 69° (old record: 62°, 1901)
Syracuse: 66° (old record: 60°, 1975)
Washington, DC:
…IAD: 69° (old record: 67°, 2001)
Watertown: 67° (old record: 65°, 1901)
White Plains: 61° (old record: 57°, 2006)
Wilmington, DE: 69° (old record: 63°, 2001)
************************************************************************************************************************************************
Posted 14 December 2015 – 01:53 PM
With each passing day of unseasonable warmth across much of North America, it is tempting to ask whether what seems like “endless October” will eventually yield to early spring-type weather. With the super El Niño only slowly fading from its peak and the Arctic Oscillation and Eastern Pacific Oscillation forecast to stay generally positive through the much of the rest of December, that may well seem like a reasonable question.
However, the case is not so clear-cut. While an exceptionally warm winter with much below normal snowfall remains among the prospects on the proverbial table, a turnaround with blocking and opportunities for at least periods of cold and snow also remain on the very same proverbial table.
If one takes a look at the latest GFS ensemble analog cases and selects those that featured a positive December Arctic Oscillation, one finds that 50% of those cases featured a predominantly negative Arctic Oscillation during the January 15-February 15 timeframe. Two-thirds of those cases that saw the Arctic Oscillation flip to predominantly negative occurred during El Niño winters.
*-through December 14.
In short, it’s a little premature to assume that much of the U.S. will feature the noted lack of winter seen in such cases as 1997-98, 1998-99 or 2011-12. If there is a lack of sustained blocking on the ensembles as the calendar approaches mid-January, then the odds may be tilted toward a winter with the dreaded combination of excessive warmth and a significant snowfall deficit. Right now, that outcome is not cast in stone.
************************************************************************************************************************************************
Posted 13 December 2015 – 04:58 PM
December 13, 2015 saw a number of record temperatures in parts of the Middle Atlantic region.
Select record high temperatures included:
Allentown: 68° (old record: 62°, 1923)
Atlantic City: 73° (old record: 69°, 1991)
Baltimore: 72° (old record: 69°, 1889)
Bridgeport: 61° (old record: 58°, 1984)
Islip: 68° (old record: 60°, 1991)
New York City:
…Central Park: 67° (old record: 64°, 1923)
…JFK: 70° (old record: 63°, 1983)
Newark: 67° (63°, 1946)
Philadelphia: 71° (old record: 65°, 1923)
Washington, DC:
…DCA: 71° (tied old record: 71°, 1889)
…IAD: 73° (old record: 71°, 1984)
White Plains: 65° (old record: 61°, 1984)
Wilmington, DE: 67°, (old record: 64°, 1923)
Basking in the today’s record warmth
Looking ahead for the closing 10 days of December, the Arctic Oscillation, which has just gone negative for the first time this month, is forecast to rebound to strongly positive values.
The end result is that the closing part of the month will likely be warmer than normal across much of the eastern half of the CONUS and parts of Canada. The New Year could also begin on the warm side of normal. Already, the trimmed objective analog pool rolled forward from the GFS ensembles suggests a better than 2-in-3 chance that such cities as Detroit, Boston, and Washington, DC could start 2016 on a mild note.
However, this warm start does not mean that January should be written off immediately. The pattern forecast toward the end of the month bears some similarities to the mean pattern that prevailed during the December 29-31, 1965 period. Sustained and strong blocking developed later in January.
A look at the objective analog pool also finds dates from late December 1957 and early January 2007 in the mix. Winters 1957-58 and 2006-07 also featured the development of sustained blocking during the latter part of winter.
All of that is speculative right now, but at least there are some glimmers of hope for a more wintry type pattern at some point down the road. For now warmth predominates and many parts of the Midwest and East could see December 2015 challenge or even break the record for the warmest December on record.
Farther west, colder weather should be taking hold during the latter part of December. Cities such as Boise, Denver, Portland, Salt Lake City, San Francisco, and Seattle could witness colder than normal weather during the last week of the month.
************************************************************************************************************************************************
Posted 12 December 2015 – 09:37 AM
A few quick thoughts this morning…
1. The 12/12 0z and 6z runs of the GFS have now moved into good agreement with the ensembles over the 11-15 day period. Unfortunately, the operational model yielded to the warmer ensemble idea. If that outcome plays out, parts of the Midwest to the East Coast would have the potential to have their warmest December on record.
2. The Arctic Oscillation (AO) has fallen to +0.622 today. It will likely go negative in coming days. However, that period will likely be short-lived with the AO returning to values of +1 or above afterward. The PNA is forecast to be neutral to somewhat negative.
3. A storm impacting the Aleutians will deepen rapidly. Its long-term implications remain to be seen. But both a similar storm in late October 1977 and Nuri in 2014 led to the development of predominant EPO blocking 30-40 days afterward.
Overall, this kind of setup favors warm anomalies in the eastern part of the CONUS (and southern Canada) with colder anomalies in the West, when colder air moves into North America and the CONUS. If one rolls forward the trimmed objective analog pool from the GFS ensembles, it looks like parts of the Midwest, Mid-Atlantic, and New England areas will likely begin the New Year just as they ended 2015 with warmer than normal readings.
************************************************************************************************************************************************
Posted 11 December 2015 – 02:54 PM
An interesting development that could have implications for the longer-range pattern evolution…
From Accuweather:
A potent storm that will cross the Aleutian Islands of Alaska this weekend could become the strongest recorded storm to impact the region.
This storm comes a little over a year after ex-Super Typhoon Nuri became the most powerful system on record to cross Dutch Harbor, Alaska, which is located in the Aleutian Islands, with a central low pressure of 924 millibars (27.29 inches of Hg).
https://www.accuweath…alaska/54125652
The 12z ECMWF at 48 hours: 926 mb
Source: Tropicaltidbits.com
************************************************************************************************************************************************
Posted 11 December 2015 – 10:07 AM
This morning there continues to be some differences between the GFS ensembles and the operational GFS in the longer-range for the eastern U.S. As has been the case for the past two days, there remains good agreement that a large part of the western half of the CONUS and southern Canada will feature cooler than normal conditions in general. However, the ensembles continue to suggest that the eastern CONUS will remain warmer than normal, though nowhere near as warm as it will be during the next several days. On the other hand, the operational GFS shows one or two meaningful cold shots reaching the East.
In the longer-range, the EPO is currently forecast to shift from positive to neutral. As a result, more cold air should be able to move into a larger part of North America.
The latest teleconnection forecasts suggest that PNA- condtions will prevail during much of the second half of December. That outcome would favor the cold’s being dumped into the West with only transient shots farther east. At the same time, the AO is forecast to go negative for a few days but then return to positive and perhaps strongly positive values.
This overall outcome suggests that the milder look on the ensembles for the East could be a more likely outcome than the colder ones on the operational GFS. However, the timeframe is very large, so things can still change. But right now, the kind of significant pattern change toward a sustained colder regime appears more likely to take place in the West than the East.
The AO forecast would be consistent with outcomes that saw more sustained blocking eventually develop in later January and then predominate in February. Interestingly enough, one of the objective analog dates from the GFS ensembles (Day 8) is 12/31/1965. Winter 1965-66 featured a strong El Niño coupled with the development of a short period of strong blocking in early January and then a strong and sustained period of blocking that lasted from 1/20 through 3/9. As the AO cannot be forecast accurately out more than a few weeks, point is that one might begin to expect more blocking than has been the case so far down the road. How much remains to be seen. A shorter-duration period of blocking similar to what occurred in 1994-95 is also plausible. Either outcome would produce more wintry weather than has been the case so far this meteorological winter.
************************************************************************************************************************************************
Posted 10 December 2015 – 10:45 AM
Though the first 10 days of December, the mild conditions would lead one to believe that the super El Niño underway has “stolen” winter. Already, the warm anomalies have been impressive, especially over the Northern Plains and parts of Canada.
Temperature anomalies for select cities (12/1-9) from the National Weather Service data are as follows:
Albany: +5.1°
Allentown: +5.6°
Atlanta: +5.3°
Baltimore: +3.6°
Bismarck: +14.1°
Boston: +5.5°
Bridgeport: +5.4°
Burlington: +5.5°
Charleston, SC: +4.7°
Chicago: +7.1°
Cleveland: +3.9°
Concord: +5.5°
Denver: +8.7°
Des Moines: +10.1°
Detroit: +3.9°
Harrisburg: +3.6°
Hartford: +4.5°
Houston: -1.8°
Islip: +5.6°
Kansas City: +7.1°
Los Angeles: +6.2°
Milwaukee: +8.4°
Minneapolis: +11.6°
Nashville: +4.1°
New York City: +6.4°
Newark, NJ: +6.1°
Norfolk: +3.7°
Orlando: +5.6°
Philadelphia: +6.2°
Phoenix: +2.6°
Pittsburgh: +3.9°
Portland, ME: +4.5°
Providence: +5.1°
Raleigh: +2.3°
Richmond: +1.9°
Savannah: +5.3°
Seattle: +7.6°
St. Louis: +5.1°
Washington, DC: +3.6°
Worcester: +6.1°
For the December 1-10 period, the Arctic Oscillation (AO) has averaged +1.544. For a meteorological winter average of -1.000 or below, the AO would need to average -1.314 for the remainder of winter. Currently, it is forecast to go negative in coming days. However, the ensemble guidance suggests that it could return to positive values later this month. This outcome could help limit the extent and duration of intrusions of colder air.
For now, even as we’ve progressed through the first 10% of meteorological winter, the weather seems to be stuck on autumn.
************************************************************************************************************************************************
Posted 9 December 2015 – 09:49 AM
The biggest story over the next seven days will be the near-record to record warmth that will spread eastward from the Midwest to the Middle Atlantic and southern New England areas. The latest GFS ensembles point to 500 mb height anomalies that will range from 2.0-2.5 standard deviations above the norm.
The MOS guidance is now showing a number of temperatures that would tie or break daily record high marks.
It still appears that cold shots in the eastern half of North America will likely be transient for the next 10-15 days. No significant Arctic intrusions appear likely. Somewhat more sustained cooler readings could develop in the western half of the U.S.
As for 12/25, the trimmed objective analog pool rolled forward remains remarkably similar to what it showed two days ago. For example, the implied readings would include: Detroit: 37-25 (vs. 38-23 from 2 days ago), New York: 44-34 (vs. 45-32 from 2 days ago), and Washington, DC: 49-36 (vs. 49-34 from 2 days ago). In terms of probabilities, they continued to indicate that the day would likely be milder than average across parts of the Midwest and eastward. In contrast, there were near equal chances of warmer or colder anomalies in the Pacific Northwest. The GEFS mean anomalies at 12/25 0z, the end of their range, were forecast to be cool in the western half of the CONUS and somewhat warmer than normal in the eastern half of the CONUS.
Finally, the current AO+ regime appears likely to yield to at least a period of AO- values within the next 5 days or so. Whether the forecast AO- period will be short-lived or more sustained remains to be seen.
************************************************************************************************************************************************
Posted 7 December 2015 – 10:27 AM
The overnight MOS readings remained impressive.
Highest Readings (12/10-13):
Albany: 60°
Chicago: 59°
Detroit: 61°
New York City: 61°
Pittsburgh: 66°
Overall, the repeated warm signal on the operational guidance and ensembles provides high confidence that some of the above cities could experience temperatures that could approach daily records in some cases.
Despite the 12/8 6z run of the GFS, which depicts a turn toward colder weather and a fairly significant snowfall for parts of the eastern U.S., the GFS ensembles have remained largely consistent with their prior runs. That scenario would favor only transient shots of cooler weather, no significant Arctic intrusions for the eastern half of the CONUS, and a generally mild pattern for Christmas Day.
For purposes of illustrating the stability of the GFS ensemble runs, the implied high and low temperatures for Washington, DC for 12/15 using the trimmed objective analog pool are 50° and 37°. During the last 3 days, the implied high temperature ranged from 48°-50° and the implied low temperature ranged from 33°-37°.
These figures should not be taken as point estimates, but merely to illustrate the stability of recent runs of the GFS ensembles in showing a milder pattern. Nothing, of course, is cast in stone from that far out. But given the context of fairly consistent ensemble guidance, it would not surprise me if the 12z GFS run flips to milder conditions at the end of its range.
Finally, the latest ensemble guidance shows a large spread among members concerning the evolution of the Arctic Oscillation (AO):
The very large and expansive polar vortex would argue that any drop to negative values could be short-lived. Since 1950, seven El Niño events featured AO+ conditions through the first 8 days of December followed by some negative values that developed between 12/9 and 12/15. There was one El Niño case (1951-52) that saw the AO remain positive throughout all of December.
Among the seven cases in question, all saw AO+ values return for at least a time during the second half of December. The median number of days during which the AO was positive during the second half of December was 11.
Those with more than 11 AO+ days during the 12/16-31 period all saw January come out with a positive AO average (Mean: +0.982; Range: +0.356 to +1.359). All of those cases then saw February wind up with an AO- (Mean: -1.091; Range: -1.806 to -0.195).
Those with more than 11 or fewer AO+ days during the 12/16-31 period all saw January come out with a negative AO figure (Mean: -0.879; Range: -2.066 to -0.148). Most of those cases then saw February wind up with an AO- (Mean: -0.290; Range: -1.473 to +1.429).
Cautiously, given sample size limitations, an above median number of AO+ days for the second half of December might suggest that sustained blocking could be delayed until late January or February. In contrast, the median number or below median number could favor earlier sustained blocking, with the greatest blocking focused on January.
************************************************************************************************************************************************
Posted 7 December 2015 – 10:27 AM
The latest guidance has grown even warmer for the December 10-13, 2015 period. The highest readings on the 12/7 0z MOS for the cities shown in #22 are as follows:
Albany: 53°
Chicago: 59°
Detroit: 62°
New York City: 60°
Pittsburgh: 69°
Although the pattern is likely to slowly evolve toward possible less exceptional warmth toward the end of December, it still appears likely that most of the cold will remain locked up in Alaska and extreme northwestern Canada. That would imply that Christmas Day in such cities as Chicago, Detroit, and Toronto could be milder than normal.
The latest CFSv2 guidance:
Below are the GFS ensembles through 360 hours. Afterward, I rolled forward the trimmed objective analog pool from the GFS ensembles to see what is implied.
It should be noted that one should not place much weight on the values themselves. Instead, what’s relevant is the idea that at this point in time, the guidance hints at a milder outcome. A lot can still change,
************************************************************************************************************************************************
Posted 6 December 2015 – 11:12 AM
During the 12/10-13 period, very warm air is forecast to sweep across the Northern Plains into the eastern U.S. The latest GFS ensembles suggest that 850 mb temperatures and 500 mb height anomalies will be 1-2 standard deviations above normal. That outcome would result in temperatures in the middle and upper 50s and perhaps even into the 60s across a number of cities from Chicago eastward to New York City.
That outcome could still change, but there has been a consistent signal on the ensembles for just such warmth.
************************************************************************************************************************************************
Posted 5 December 2015 – 11:17 AM
December has started with much above normal readings in a large part of North America with the exception of parts of the West. The trimmed objective analog pool from the GFS ensembles still favors warmth across much of December as a whole.
Recently, there have been some changes in the long-term teleconnections forecast.
1. The PNA, which had been forecast to go negative is now forecast to remain generally positive. This outcome is what one would typically see during a strong PDO+ (October value: +1.47).
2. Numerous ensemble members forecast the AO to go negative. It remains to be seen whether that forecast will hold or blocking will prove transient should it develop.
3. The EPO is forecast to remain generally positive.
Both the teleconnection cases for the 12/15-25/1950-2014 period and the extended range of the GFS ensembles point to a reasonably consistent 500 mb pattern:
Finally, it should be noted that some of the teleconnection cases e.g., December 1965, evolved into a colder January. The trimmed objective analog pool had fewer cold outcomes in January. Nevertheless, it’s too soon to really speculate on January, but December’s largely warm outcome has been reaffirmed by the early data coupled with the latest guidance (objective analogs, ensembles, and teleconnection cases).
************************************************************************************************************************************************
Posted 1 December 2015 – 01:50 PM
At the start of December, the Arctic Oscillation (AO) was +1.497 and the Pacific-North American Pattern (PNA) Index was +0.801. Over the next 15 days, both indices are forecast to remain generally positive to strongly positive.
Typically the kind of strong and expansive polar vortex responsible for the current AO+ regime is slow to break down. Therefore, it is likely that December will feature a predominantly positive AO. At the same time, the ongoing strong PDO+ typically favors a PNA+ pattern. It is probably more likely than not that the PNA+ will also predominate during December.
If one takes a trimmed set of 500 mb analogs from the 12/1/2015 0z run of the GFS ensembles (the years that showed up in both the 6-10-day and 11-14-day sets), those cases typically saw December’s AO and PNA average > 0. Perhaps reflecting the slow breakdown of the kind of polar vortex currently in place, January also typically saw an AO average > 0. However, the AO cannot be forecast accurately for more than a few weeks’ time, so the January outcome is speculative.
Nevertheless, the current polar vortex leaves open the possibility that the AO could be predominantly positive for the winter as a whole, even if blocking develops in January or February. It’s too soon to make that call given the forecasting limitations on the AO.
Finally, the trimmed analog pool features a lot of warmer than normal anomalies in North America with near normal or cooler anomalies in parts of the West. That idea is similar but not identical to the last CFSv2 forecast for December (11/30/2015 run). Moreover, toward the end of their range, the GFS ensembles suggest that a generally zonal and warm pattern across North America may begin to yield to a cool West/warm East scenario.
************************************************************************************************************************************************
Posted 29 November 2015 – 06:35 PM
Even as meteorological winter looks to get off to a mild start across much of North America, especially parts of central Canada, it is worth starting a thread for medium-term discussion.
Currently, one of the strongest El Niño events on record is underway. That event will likely play a critical role throughout the winter, even as the guidance suggests that it has peaked or is near its peak.
Teleconnections will be crucial. With the strong PDO+ underway and likely to persist through meteorological winter, the PNA+ should be favored. That coupled with a negative EPO could allow colder air to eventually overspread North America.
However, at present, the EPO is forecast to remain positive through mid-December.
In addition, the Arctic Oscillation (AO) is also strongly positive. Strong and expansive polar vortices usually require a measure of time before they erode. Indeed, 7 of the 8 cases since 1950 that saw the AO reach or exceed +3.000 during the November 20-December 10 period wound up with predominantly positive AO values for December. During such cases, December typically wound up warmer than normal across much of North America.
All of the major monthly guidance currently suggests that December will likely wind up warmer to perhaps much warmer than normal. The GFS ensembles are show widespread warmth through 15 days.
The big question concerns if or when the polar vortex will begin to break down. It has done so in a number of winters from the above sample, with 1972-73 and 2007-08 being exceptions.
In any case, below are some images from seven of the eight winters above that saw December’s AO average > 0 (all and the El Niño subset) for the U.S. and Canada. The GFS ensemble forecast for days 6-10 and 11-15 are also posted.
