(Blog Written by Donald Sutherland)
July 16-23, 2012 Thoughts:
Even as the heat is likely to ease back after this coming weekend, the respite may prove short-lived. The evolving pattern could lead to a new outbreak of heat during the third week of the month.
Recent guidance has forecast a new trough to push into the Pacific Northwest with a diving PNA after mid-month. Such a development would be consistent with what appears to be a trend for more frequent strong negative PNA values (-1.00 or below). The number of days with the PNA reaching -1 or below was as follows for the April-June timeframe:
April: 2 days
May: 3 days
June: 6 days
The charts below are as follows:
Top Left: The composite temperature anomalies for ENSO Region 3.4 anomalies of +0.20°C to +1.00°C, a PNA of -0.50 to 0.50, and an AO of +0.50 to +1.50 for North America.
Top Right: NAEFS for the July 13-19, 2012 timeframe
Bottom Left: 7/5/2012 GFS Ensemble 11-15-Day anomalies (7/16-20/2012) from RaleighWx’s page
Bottom Right: July Decadal Temperature Trend
It should also be noted that the Arctic region remains warmer than normal. This could also limit the magnitude, expanse, and duration of any chilly air masses.
Taking into consideration the upstream conditions, teleconnection analogs, ensemble guidance, and decadal trends, I expect the following for the July 16-23 timeframe:
– Warmer than normal across most or all of Canada, possibly much warmer than normal across central Canada
– Near to perhaps somewhat cooler than normal across Texas and the Western Gulf states
– Cooler than normal in the Pacific Northwest
– Warmer than normal across the rest of the U.S. The warmest anomalies will likely cover the Central Plains to the lower Great Lakes region and perhaps into the Middle Atlantic states.
Finally, given some of the monthly analogs, there remains the potential for some excessive heat beyond the July 16-23, 2012 timeframe.