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Potential for major winter storm late next week, but also major question marks

Forecast models have converged on the idea that a significant storm will impact the area between next Thursday night and Sunday. If they are right, it could bring us our first meaningful winter weather event of the season. There is some chance this could produce heavy amounts of snow on parts of the region.

Next chance of accumulating snow: January 21-24
Percent chance of at least one inch: 30 percent (low probability mainly due to number of days away)

Not unsurprisingly six days out, a boatload of uncertainty still exists concerning the storm details. The models continue to jump from solution to solution. Until they reach a consensus, making a definitive forecast so far in advance is foolish.

A wide variety of solutions varying from one that would produce significant snowfall to one that would give us little or no snow are still possible. Like most potential storms the devil is in the details and right now, we don’t have a clear idea of where the storm will track relative to D.C. or how much cold air will still be around when the storm reaches us.

Some models take the primary storm to our north which would kill our snow chances while others like European and U.K. model show a favorable storm track for snow. There are even a few simulations that have the storm missing us to the south. Readers need to monitor forecasts closely during this week. The storm has potential to produce a significant winter storm or to be a dud, leaving snow lovers depressed.

Model discussion

Today’s European, GFS and Canadian models do a pretty good job of displaying how much uncertainty exists in the storm track.

The European model had been consistently suppressing the storm too far south to give us any precipitation. But last night’s and today’s version (see below) jumped the low track to an ideal one for a Washington snowstorm. Even with a favorable track, the surface temperatures are precariously close to freezing just east of the city. Any westward jog to the track would probably push the freezing line back towards or even a little west of the city.

Note the UK Model has a similar solution to the European, forecasting the storm to take a more-or-less ideal track for heavy snow in the D.C. area.

The last two runs of the GFS have offered more of a mixed bag of precipitation tracking a low northward to Kentucky before reforming it to our south. That almost always leads to precipitation type questions with the areas west of I-95 getting more snow than the city and points east. However, last night’s GFS simulated high pressure to our north in a favorable position to facilitate cold air damming suggesting that the low level cold air might be stubborn and linger across the area.

This morning’s GFS has a weaker high to the north and doesn’t hold the cold air in as long (see below). It pretty much takes the rain-snow line right through the city. Like the European, it would offer a winter storm but one that might give us a mix of snow, sleet, and freezing rain. However, if the low tracks a little farther to the north and is slower to redevelop to the south, the wintry look might fade to one giving us some snow at the onset but then mostly rain.

Alternatively, a more rapid transition to a low along the coast would offer a snowier look. That’s the knife edge that our snowstorm chances are almost always balanced on. Slight changes to the track and intensity of a low can make a huge difference to the forecast.

The suite of simulations of the low pressure center position on Saturday morning from the European model ensemble, shown below, gives a good sense of the range of possibilities.

Low pressure centered just off the North Carolina Outer Banks is an ideal position for snow in the D.C. area.

Last night’s Canadian model showed more of a rain storm than a snowstorm. It did offer snow at the onset of the storm but tracked the low to Ohio before any secondary low formed. Such a track would promise D.C. mostly rain but could offer an ice storm in our western suburbs.

Today’s Canadian model tracks the low a tad south of last night’s run but still tracks a low to eastern Kentucky before reforming the low over southern Virginia (see below). It’s late reforming the low and therefore would change the snow to rain across D.C. Note that by 7 p.m. Friday both the surface and high altitude (5,000 feet) freezing lines are west of the city suggesting mixed precipitation or rain for close-in D.C., with a snowier scenario for the far western suburbs.

So what do we know? There is likely to be a storm impacting the Mid-Atlantic region sometime starting as early as Thursday night and ending as late as Sunday. The storm has potential to produce winter weather but also has the potential to be mostly a rain storm or even a miss to our south though the latter right now seems a long shot. Snow lovers, this is our first legitimate snow threat of the season but still is one that could disappoint.