(Blog Written by Donald Sutherland)
August 2012 Forecast:
The hot and dry summer of 2012 will go on.
Key Assumptions:
• A weak El Niño event will be underway in August
• The AO will likely be somewhat positive
• The PNA will likely be somewhat negative
The top analog was 2006.
The charts on which my August idea is based are:
Top Left: Analogs for August 2012
Top Right: Analogs (Temperature and Drought) for August 2012
Bottom Left: CFSv2 Forecast for August
Bottom Right: Observed decadal temperature trend
Although the GFS ensembles have hinted that the Arctic region could grow slightly cooler than normal toward the end of July, the GFS ensembles have recently been somewhat too cool there. The assumption is that the Arctic region will likely be somewhat warmer than normal. Hence, the source region of potential cool air masses will have less cool air than usual available.
At the same time, on account of the increasingly widespread drought, the Southwestern and Plains States will remain unusually dry. This means more of the sun’s energy will be devoted to direct heating relative to evaporation of soil moisture. As a result, hot air masses that come eastward will be warmer than usual.
To date, Summer 2012 has been exceptionally hot in the Northern Hemisphere. As per the latest NCDC data, the Northern Hemisphere’s land area had a June temperature anomaly that ranked highest on record (2.42 sigma above the 1981-2010 climate baseline). The combination of less cool air than usual in the Arctic, drought across a significant portion of the U.S., and general exceptional warmth in the Northern Hemisphere all suggest that odds favor a warmer than usual outcome than is typical for the onset of an El Niño.
As a result, my thoughts are as follows:
– Alaska will be mainly cooler than normal
– The West Coast of the U.S. perhaps into British Columbia will be somewhat cooler than normal
– The remainder of North America will be warmer than normal. An area running from the Southern and Central Plains into the Great Lakes region (U.S. and southern Ontario) could be much warmer than normal. Another area in northern Canada could also be much warmer than normal.
The ongoing drought has increased in expanse and severity in recent weeks. The July 10, 2012 Drought Monitor reported that 60.84% of the U.S. was experiencing moderate or worse drought conditions and 11.61% was experiencing extreme or worse drought conditions. As a result, it makes sense to discuss precipitation outlooks.
2012 saw the 10th driest June on record in the contiguous U.S. 19 of the 30 driest cases in June were also among the 50 driest cases in July. July 2012 appears well on course for that outcome. 11 of 19 or 58% of those dry July cases were also among the 50 driest cases in August.
From that pool of cases, I selected the years that showed up most persistently as summer analogs. Two stood out: 1953 and 2002. 2002 was the top analog for July.
The charts below are:
Left: Drought Analogs
Right: CFSv2 Precipitation Forecast for August
My thoughts are as follows:
– The Central and Southern Plains will remain drier than normal in August
– Dry anomalies will likely expand across the Ohio Valley into New England
– The Gulf Coast and Southeast could experience near normal precipitation
– With the exception of the Southwest, which should have near normal preciptitation, the rest of the western third of the U.S. could be wetter than normal
Finally, some historical photos from the Dust Bowl are below:
