The Coming Storm

No, not that one. Or that one. I mean the literal one, this one, the first big winter storm of the season. Here is the situation as of this morning (map forecast for 8am ET Wednesday, the storm is the “L” off the Georgia Coast):

Winter storm forming over Southeastern US … GFS model of precipitation type and moisture transport.

Like hurricanes, winter storms have to have a mix of conditions come together to cause them to grow and evolve. The key to weather on the earth is the need to balance the warm, moist air from the tropics with the cold, dry air over the poles. This happens in a number of ways, but in the summer the most dramatic are of course hurricanes. In the winter, it’s nor’easters. A classic nor’easter starts out as a low pressure system just off the coast of the Southeast. It moves northeast along the coast, carrying with it the warm moist air of the Gulf of Mexico and Bahamas, pushing that air inland where it meets cold polar air. It is along that swath where the air masses collide that the potential problems for Humans comes in. The danger this morning lies Appalachians and western North Carolina where the precipitation may be in the form of freezing rain, as well as inland in Kentucky (on the map, the red/purple area). Here is what things should look like this evening around 7pm. Notice that the low is deeper (stronger), the blue moisture transport vectors are longer (stronger), and across the New York/Pennsylvania area snow will be falling. The zone of freezing rain will by then have shifted to western Virginia.

The situation tonight …

By tomorrow morning the Low should be more elongated and off the Massachusetts coast, still pumping moist, snow-laden are into the NorthEast. The storm should be off the Canadian Marine Provinces by Friday.

Thursday Night

In terms of impacts, again the big concern is the area where freezing rain and ice will be falling. For the Northeast, snow could be fairly deep in places – some forecasts are for up to 24″ – but it’s more likely to be disruptive rather than truly dangerous, and again conditions should clear out by this weekend. For the Deep South (GA/SC), this will be a rain event, even for North Georgia. As things continue to cool off with the approaching winter season, the risk for ice storms will move further south … but the impacts of this event will be in North Carolina and the NEUS. How should you prepare for winter storm season? Take a look at the FEMA/DHS Winter Storm page for tips …

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