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Posted at 02:46 PM ET, 12/21/2011

Christmas snow? Probably no!

A few media outlets have started hyping the potential for a snowstorm either on Christmas eve or Christmas day. This morning Yahoo headlined a Good Morning America article, “Nor’easter could bring white Christmas to millions”. The article said: While blizzard conditions may have ended over the U.S. for now, a Nor’easter is now a possibility for December 24 - 25, which might mean a white Christmas for major cities along the East Coast from Washington, D.C. to Boston and hectic travel conditions for millions.

The Capital Weather Gang strongly disagrees that there is the potential for a big Christmas weekend snowstorm along the East Coast.

There is just a very slight chance of non-accumulating snowfall for the Washington area but no true nor’easter is in the works. A more likely scenario is for either light rain or for the weak wave to skirt us to the south bringing the area little or no precipitation on Christmas Eve or day. The latter scenario right now seems the most likely.


Today’s European, Canadian models and GFS are all now calling for a suppressed storm track keeping precipitation out of the area for the most part. If anything, during the past 12 to 24 hours, the models have trended away from the potential for any major winter storm.

GEFS ensemble members (different runs of the same model with slightly different initial conditions) (Penn State)

The GEFS ensemble run from 1:00 a.m. (above) was not very supportive of a major snowstorm. The only member that produces a wave strong enough to bring precipitation to the area (top left panel) is the control run (essentially the operational model run with a coarser grid). All the other members are much different with the timing of the wave and none support the overnight GFS model run which still only forecasted light precipitation with temperatures remaining in the mid-30s.

The ensemble members either suppress the wave or bring it out more slowly. And by the time it gets to the East Coast the air mass has moderated too much for snow.

Last night’s European model had a more suppressed look that would offer some sprinkles while the UKMET model kept any storm too suppressed to bring any precipitation into the region. None of the models had a strong low tracking up the coast.
This morning’s GFS 500 mb height and vorticity (spin) forecasts valid at 4 p.m. Christmas eve (left) and 10 a.m. Christmas day (right) (NOAA)

This morning’s 7:00 a.m. GFS run has shifted back towards the solution offered by the majority of last nights’ ensemble members, one with a suppressed low track that would bring no precipitation to the area. The northern stream of flow across Canada and the northern U.S. is strong and overwhelms the southern stream shortwave.

At 4 p.m. Christmas eve the southern stream disturbance (trough) is over Texas and Oklahoma (left panel). By 10 a.m. Christmas morning the strong northern stream and an associated upper level system digging across the Great Lakes pretty much puts the kibosh on the southern stream system.

Note by Christmas day the southern stream system has weakened and almost disappeared. Such a scenario is not uncommon during La Nina winters especially with the Arctic and North Atlantic Oscillations are positive and there is plenty of flow across western Canada.

This morning’s GFS surface pressure pattern, 6 hour precipitation, 2 meter temperature forecast valid at 10 a.m. Christmas morning. (NOAA)
The pattern also makes it hard to hold in cold air. Air moves from higher to lower pressure. Note on the image to the right that the pressure over the Great Lakes and Canada is lower than the pressure in Virginia. Therefore, no new cold air is feeding southward and the surface zero line (blue line) ends up being well to our north by 10 a.m. Christmas morning (see below). Even if the precipitation shifted back north, it is doubtful that temperatures would be cold enough to support snow. For the romantic guys and gals that would like to see snow for Christmas, this pattern is the pits.

In summary, I don’t see any potential for a major snowstorm and only think there is a very small, almost non-existent chance of anyone in the area seeing snow falling on Christmas day. The most likely scenario is for the storm to skirt us to the south missing us.

How does the remainder of the year look? The pattern continues to be one that favors temperatures averaging about normal during the week leading up to New Years as Pacific air sweeps across the country. The Snow Lover’s Crystal Ball is likely to be unused through the New Year.

By  |  02:46 PM ET, 12/21/2011

Categories:  Latest, Winter Storms

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