Tuesday 9 a.m.
The upper-air current arriving in Pennsylvania this week originates over the Gulf of Mexico, so it is no surprise the main weather theme is warmer and more humid than typical for the season. However, computer models suggest that on Sunday, the flow reaching Pennsylvania will have originated in western Canada. Translation: warmer, then chillier. This video has more:
The details of the weather pattern are far less clear-cut than the overall trend. For example, there has been rain, some heavy, in a corridor extending from Pennsylvania to Virginia. Pittsburgh has been near the western edge; Philadelphia just east of the eastern edge. Farther south, violent thunderstorms developed in east-central North Carolina. Here is a map showing where precipitation was at 10 a.m. EDT.
This map shows the pressure analysis for the Northeast and Great Lakes. The gusty flow on the west side of the low pressure area adds a real autumn feel to the air.
Since individual lines and clusters of thunderstorms have limited life spans and change character constantly, forecasting whether it will or won't rain at any one time this weekend is difficult at best. One solution is to have your tablet or phone available with the AccuWeather.com app so you can see where all the storms are at the times when it concerns you the most.
It does look warmer for the weekend, but every time the warm air tries to extend into New England it gets chopped down. There could be more showers at times Sunday and early next week as forest we can tell. If any forecast gives you a headache, why not take a friend's advice: Take two aspen; sequoia in the morning.
This map from 5AM ET shows the cold front that is continuing toward this Northeast and Middle Atlantic states. Temperatures stayed up in the 70s all night ahead of the front but it turned noticeably cooler after the front moved through.
The cold front that will cut off the heat will generate strong gusty thunderstorms as it moves southeastward today. The National Weather Service Storm Prediction Center highlights the most likely area for these severe thunderstorms today and tonight.
As the high pressure area in the Northeast moves away, the the southwesterly flow pattern will shift eastward. This means Wednesday could be the hottest day of the week from D.C. to Boston. A cold front will follow.