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!
It appears likely that many normal activities can go on through the day Monday, as long as the typical cautions for light to moderate snowfalls are observed. Tuesday will be an <strong>entirely different story</strong>. This map shows the GFS- predicted snowfall through 7 P.M. ET Monday:
The second storm we have been talking about will affect the Middle Atlantic region late Sunday and Sunday night. This GFS forecast map is for 7PM ET Sunday and shows precipitation amounts for the 6 hours up to that time.
This was our snow accumulation projection as of mid-morning. A storm that will develop in the Midwest on Sunday is likely to track to the Virginia-Maryland coastal area by Monday morning, then turn east. It will probably bring some to snow places that get mostly rain out out of the first storm.
Just a 1- or 2-degree temperature difference in the lowest 5,000 feet of the atmosphere can make the difference between heavy wet snow and heavy wet rain. Here is a draft of our snowfall map from mid-morning.
Much can still change with regard to the Saturday storm. This draft map from this morning shows how the accumulations may turn out. The AccuWeather.com staff will be watching this closely. I am happy to see many of our newer forecasters making major contributions.
n the Northeast corridor, this winter has not created much happiness among people who like snow. In New York City, this is the first year out of the last nine to have no 2-inch or greater snow event to this point in winter. Ralph Fato (WxNut27) sent out one of his wonderful charts to illustrate the widespread lateness of the first significant snowfall: