The American (GFS) model forecast of a storm system tracking through the Washington region this weekend.

Computer model forecasts are still bouncing around, but there is reasonably strong agreement that the Washington region should see at least some snow this weekend and perhaps several inches or more.

The most likely time for any snowfall is between Saturday night and midday Sunday, but depending on the model, it could begin as early as Saturday afternoon and end as late as Sunday afternoon.


(Washington Post/Washington Post)

Confidence has increased over the past 24 hours in the possibility of accumulating snow, and we now think there is at least a 40 percent chance of an inch and about a 25 percent chance of at least three inches. These are conservative probabilities and will rise further unless models back away from their current forecasts, which average around 3 to 6 inches for the storm.

On Monday, the American and European models conflicted on whether a storm system this weekend would produce very substantial or very light precipitation. Now it seems they have met in the middle and agree that a light-to-moderate snow event is most likely.

However, the potential winter storm is still about five days away, so models could shift toward less snowy or snowier solutions.

Cold air is predicted to be firmly entrenched over the region because of a strong area of Canadian high pressure to the north feeding freezing air into the storm. Temperatures while snow is falling may be mostly in the 20s.

“This doesn’t look like it has the makings of a blockbuster storm, but it could still produce enough accumulating snow to cause slick driving conditions,” said Wes Junker, the Capital Weather Gang’s winter weather expert.

Big wild cards are how strong the storm will become and its track. A weaker storm that passes far south of the region would result in only light snow and minimal accumulations, if any. A stronger storm that moves from near the Gulf Coast to around Cape Hatteras, N.C., would potentially produce significant snow of at least several inches.

“Right now, most of the models suggest a track far enough north to give us moderate snow, but there still is enough wiggle room not to completely rule out just a little snow or a more significant snowstorm,” Junker said.

This is another storm, similar to the one in early December, in which the heaviest snow is likely to occur south of Washington in central and southern Virginia.

Let’s break down what the models project:

  • The operational American (GFS) model suggests light snow or flurries could break out Saturday afternoon and perhaps become moderate overnight Saturday into Sunday morning before ending. It projects about three inches of snow.
  • The experimental American (FV3) model holds off the onset of snow until Saturday evening but forecasts moderate to heavy snow after midnight into early Sunday. The snow ends before noon Sunday but not before putting down 6 to 8 inches of precipitation.
  • The Canadian model begins light snow Saturday night, turning it moderate to heavy early Sunday. Snow tapers off to light snow or flurries by midday, ending Sunday afternoon. The model predicts about six inches of snow.
  • The European model suggests some flurries are possible as early as Saturday afternoon and evening but holds off an accumulation of snow until early Sunday, continuing into the afternoon. It predicts 4 or 5 inches of snow.

The bullet points above are forecast summaries for the primary or operational simulations of the models. But some of the models have a larger group of simulations that provide additional forecasts.

In the American modeling system, about half of the 20 simulations forecast at least six inches and a few show the potential for 10 inches or so. However, there are also several that forecast an inch or less, suggesting a minimal snow event or nonevent is still on the table. The average simulation forecast is about six inches.


Snowfall forecast through the weekend from the simulations in the American (GFS) modeling system. (WeatherBell) (WeatherBell.com/WeatherBell.com)

In the somewhat-less-snowy European modeling system, about one-third of the 50 simulations forecast at least six inches. The average simulation forecasts about four inches.

This weekend event has the most snow potential of any storm so far this season in the region, but there is still substantial uncertainty on the specifics. Anything from just light snow and flurries to six inches or more of snow is possible. We’ll try to narrow the forecast in our next update, which is Wednesday.