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!
This satellite picture shows clouds over parts New York and Pennsylvania, as well as areas of low clouds, fog and snow cover from Michigan to Illinois. Most of the Northeast should have at least some sunshine through Thanksgiving Day.
As we go through the week, the flow aloft over the East will become southwesterly. This will promote a major warmup. This map shows the projected upper-air flow for Thanksgiving afternoon:
A major snowstorm will affect the area from Iowa to Michigan tonight and tomorrow. At first, snow can melt on streets, but as it continues and the temperature drops, the area impacted by slippery conditions will increase dramatically. This map shows expected accumulations:
This map shows two cold fronts in the northeast quarter of the nation; 9 a.m. ET temperature are plotted. The isobars are closest together over the central and western Great Lakes, and this is where the strongest winds were occurring.
This map shows how large an area is directly affected by precipitation on Tuesday morning. The low pressure center was in Kansas early today but will move all the way to Hudson Bay by Thursday while sending a cold front eastward on its south side.
A storm now moving through the Rockies will tap moisture from the Gulf of Mexico to threaten the central state with flooding rain. This map shows the GFS-predicted rainfall for the period from today through midday Friday.