Snow chance edges up modestly for late Wednesday, especially west of D.C.

A weak upper level disturbance zips by to the south Wednesday, as cold air filters into the area.  This combination could produce some light snow, or a mix of rain and snow, Wednesday into Wednesday night.

GFS model shows some light to moderate snow having fallen as of 7 p.m. Wednesday night, with the freezing line right around I-95. (StormVistaWxModels.com)

GFS model shows some light to moderate snow having fallen as of 10 p.m. Wednesday night, with the freezing line right around I-95.  Low pressure developing to our east is trying to pull down some cold air. (StormVistaWxModels.com)

Whether accumulating snow materializes depends on whether the upper level system ends up producing a low along the coast close enough to bring us precipitation while also pulling in some cooler air from the north and west. This morning’s GFS offers such a solution, developing a low that would produce snow Wednesday afternoon and evening (see above). Right now it is an outlier, but not an impossible solution.

GFS model simulates light snow accumulation (through 7 a.m. Thursday), mainly west of the District (Weather Bell.com)

GFS model simulates light snow accumulations (through 7 a.m. Thursday), mainly from D.C. and west. This is a simulation and actual results will vary. (Weather Bell.com)

 

Most other models are less bullish on accumulation prospects for one or more of these three reasons:

1) Most predict that a low passing to the north will  supply southerly winds out ahead of the inbound cold front resulting in above freezing temperatures. So any light snow that falls would have trouble accumulating or may mix with rain, especially along and east of I-95

2) The precipitation rates and total precipitation on most models are light. Among the SREF suite of model simulations, the few that are depicting heavier precipitation are predicting mostly rain. (See below.)

Precipitation accumulation over time from different model simulations (from the SREF model).  When lines are increasing, it indicates falling precipitation in the different simulations. When lines are flat, it indicates no precipitation. Green lines indicates rain, blue snow.

Precipitation accumulation over time from different model simulations (from the SREF model). When lines are increasing, it indicates falling precipitation in the different simulations. When lines are flat, it indicates no precipitation. Green lines indicates rain, blue snow.

3) Some models dive the upper system so far south that the precipitation stays to our south or out to sea

The Canadian and European models show little, if any snow from the District and points east, and just light amounts to the west.

Canadian model shows very light snow amounts through Thursday morning, except towards the mountain of Virginia and West Virginia. (WeatherBell.com)

Canadian model shows very light snow amounts through Thursday morning, except towards the mountain of Virginia and West Virginia. (WeatherBell.com)

European model shows very light snow amounts through Thursday morning. (WeatherBell.com)

European model shows very light snow amounts through Thursday morning, mainly west of D.C. (WeatherBell.com)

The NAM model, not shown, simulates no precipitation (but is a bad model more than 48 hours into the future).

Right now, we favor a period of “conversational” light snow (non-accumulating for the most part), possibly mixed with rain near town and to the east, with light snow accumulation possible towards Loudoun and Frederick (Md.) counties.

Probability of 1″ of snow in immediate D.C. area: around 20 percent.

Probability of 1″ of snow in Loudoun and Frederick Counties: up to 30 percent.

We’ll offer more specifics tomorrow.

A repeat situation is possible Friday or Friday night. This system looks similar to Wednesday’s with many of the same issues: a low riding to our north,  marginal temperatures for accumulating snow, and a lack of moisture.  Believe it or not,  a third such system could come through the region Saturday night – though temperatures may be slightly cooler.

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