Wednesday 8 a.m.
A large high pressure area over the Northeast maintains dry weather in the region. As the high pressure area drifts offshore, south winds will promote warming. Farther west, a flow from the Gulf of Mexico sweeps north toward the Great Lakes, and we see showers and thunderstorms developing. In this video, we show how the rain should eventually spread east as a cold front moves slowly from the Midwest toward the East Coast.
Once the cold front arrives in or near the I-95 corridor, many possibilities open up. Two of them are shown on these maps. Last night's GFS showed a low pressure area from then the Gulf states latching on to the front to bring rain to the Middle Atlantic states Monday. The European model shows the same storm but has it moving more slowly and expanding its influence farther north and west. This map shows those two solutions. I expect more changes on both models during the next few days.
For example, the purple line in the east marks the boundary between air coming in from the ocean and a southwesterly current of warmer air. That boundary was the scene of showers and thunderstorms when it was in the middle of Pennsylvania yesterday, and was associated with rain that moved through the Hudson Valley early this morning.
Looking ahead to late next week, some of the computer models suggest a hurricane could affect areas between the Gulf of Mexico and the Atlantic east of the Bahamas. We are entering the prime part of the Atlantic hurricane season, but at this point there is only one model I am prepared to accept:
The following map shows the individual members of the forecast for the 5,880-meter height line at 500mb. If the 500 mb height is that high, it usually means the weather at the ground in the Northeast is hot. However...
This pressure analysis was made using 9 a.m. ET data. The thin west-east black line is the boundary between hot and cool weather. A low pressure area is moving eastward along the boundary zone, causing showers and thunderstorms. The next low pressure area should send some of the rain farther north.
In the early to middle parts of next week, we expect to see a boundary zone separating hot, humid air to the south from cooler air to the north. A series of ripples or disturbances aloft moving west to east will take turns at enhancing or reducing the chance of showers and thunderstorms.
Looking beyond next week, we see signs of something that has been missing in the Great Lakes and Northeast just about all summer: hot weather. That may change. Here is a computer model prediction of the upper air flow on Sunday, Aug. 24. Note how the flow appears to run from Arizona all the way to north of New England.