[Euro computer model forecast at 500 millibars for September 7th]
August has brought a continuation of below normal temperatures to the Mid-Atlantic region following a slightly cooler-than-normal month of July, but it looks like at least the first half of September will be on the warmer-than-normal side. The persistent upper air pattern of recent months featuring numerous troughs of low pressure centered over the Midwest and Great Lakes will change over the next several days to one with strong high pressure ridging centered in the Southeast US. Indeed, the 500 millibar forecast map from the latest European computer forecast model run (above) depicts high pressure in the Southeast US about 10 days from now. From this position, high pressure over the Southeast US will pump in warm, humid air from the Gulf of Mexico region to the Mid-Atlantic which until now this summer has not been sustainable by the atmosphere for more than a couple of days at a time. Supporting evidence for this warm outlook during the first half of September comes from NOAA’s Climate Forecast System (CFS version 2) forecast model which shows warmer-than-normal conditions during the first 10 days of September in much of the eastern half of the nation (orange/red areas in two maps below). Looking even farther ahead, I believe it is possible that the warmer-than-normal weather pattern that develops next week may end up continuing into October, but there is likely to be a transition back to colder-than-normal conditions before the winter locks in.
[NOAA/Climate Forecast System forecast maps for temperature departures from normal for the next two weeks]