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.
Tropical Storm Erika could eventually affect Florida and other sections of the Gulf Coast or Southeast, but for now it poses no threat for the Northeast. This map shows the storm as of early this morning.
The second concern is Erika. The map below shows what many different models area saying. While there is a good agreement in the short range, the longer-range spread is quite larger, with tracks ...
This picture shows where Erika is. The various models show a track toward Florida with a lot of uncertainty after that. If it does make it to land, then moves slowly (steering forces look weak), it could be a major rain producer.
It is way too early to be definitive about these storms, but the many models being used in predicting the track have closer agreement than many storms have at this point.
On this satellite picture, you can see a cold front approaching the Appalachians. That front helped produce thunderstorms in the Midwest yesterday, but that activity died out overnight. It is likely to reactivate today, with...
...shows a north-south trough line over New England. Moist air will approach this line from the southeast while northerly breezes bring in dry weather west of the line. As the front stalls then slowly backs up, some moisture can spread westward later in the weekend.