Wednesday Afternoon Weekend Snow Update

Computer models remain quite uncertain on the details of the storm that will likely be in the vicinity of the Mid Atlantic region over Christmas. About the only agreement among the models is that the storm will arrive a little later in the period, most likely Sunday into Monday.

I have annotated the late afternoon visible satellite image showing the position of the storm coming on to the west coast and the estimated track across the U.S. over the next few days. Note that the storm will likely dip to the Gulf coast as it moves eastward, picking up moisture before it moves up the East Coast.

The key is that move up the East Coast and how close the track will be to the coast. This is where the various computer models fall into two general camps. One, some distance from the coast with less snow and, the other, close to the coast with more snow.

The two forecast maps below show that difference, showing estimated storm positions during the pre dawn hours on Monday.

Both of these forecasts are from the Wednesday morning model runs. The top map is the GFS model(American) and shows the storm to be farther off shore than the bottom map (ECMWF-European).

The GFS MOS “numbers” show how an easterly track reduces the snow potential.

The yellow outline highlights the Saturday night through Monday morning timeframe. The blue outline highlights the precipitation probabilities at 6 and 24 hour intervals (less than 50%) with the “1” indicating less than a tenth of an inch of liquid equivalent precipitation. The red outline indicates that the type of precipitation would be all snow and the “1” indicates that up to two inches would be possible. Several days ago this very same MOS product projected up to and perhaps more than six inches of snow.

The European “operational” model has been consistent in developing a powerful storm close to the coast which would result in significant snowfall over the area. An ensemble of various ECMWF interpretations position the storm farther east however with somewhat lesser impact. So, even within a particular model there is no firm consensus.

The bottom line is that there is too much conflicting information on what the storm’s impact will be on the area once it gets here. A National Weather Service discussion on that very subject puts it best:

We will just have to sit tight and wait for more information.

Stay tuned,

John Collins


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