Thursday 10 a.m.
The upper-air feature that has been pumping warm, moist air northward through the Eastern states is getting kicked northeastward by a wider trough that is taking shape farther west. The latter feature is sponsoring the southward push of colder air. Near the core of the cold air mass, temperatures dropped as low as the teens in parts of Montana. A few places had their coldest morning since last winter. In eastern North Dakota, Fargo was hit by gale-force, icy wind gusts carrying the first snow of the season.
The main thrust of the cold air will be across the upper Great Lakes and Ontario, but the leading edge of the change to cooler weather has already reached northern Texas. At Amarillo, it was 64 degrees at midnight with the wind out of south. At 8 a.m. CDT, it was 49 with a north wind gusting past 40 mph! The change to chilly will not be as dramatic when it reaches the East Coast, but it will certainly be noticed. Temperatures will be well up in the 70s in Boston tomorrow... and near 80 degrees in Philadelphia and Washington, D.C. On Sunday, temperatures in those cities will be in the 40s and 50s.
This morning's NMM-WRF run shows the band of rain associated with the leading edge of the change to colder weather crossing the Appalachians by midday Saturday. The rain shown on the map is the predicted amount from 8 a.m. until 2 p.m. EDT.
In the six-hour period after this (2 p.m. until 8 p.m. EDT), the rain band almost totally vanishes. I interpret the maps as suggesting I may not actually need the rain jacket that I will carry along anyway to the Penn State - Northwestern game on Saturday. I always carry the jacket in my golf bag so that if it does happen to rain, it looks like I predicted it all along!
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.