If this past weekend didn’t convince you winter is not over yet, the coming weekend very well may. Computer models are suggesting a winter storm could develop and bring snow or cold rain to the region.

The most likely timing for any storminess would be Saturday night into Sunday — although that could shift some. Forecast uncertainty is very high and there still is no clear consensus on whether the storm will provide us with accumulating snow, plain old rain or miss us to the south.

We see three most likely scenarios for the weekend weather:

1. Snowstorm scenario (40 percent): The storm tracks across Southern Virginia or North Carolina, keeping us on the cold side of the storm and offering us accumulating snow. It’s too soon to predict how much snow would fall. In this scenario, we allow for the possibility of a mix of snow and rain — especially in our warmer areas from the District and to the south and east.


This morning’s GFS model simulation of weekend storm.

2. Rain scenario (40 percent): The storm tracks almost right over us or just to our north, pulling up enough warm air to keep us getting mostly rain. In this scenario, we allow for the possibility for some non-accumulating snow to mix with rain, especially in our colder areas to the north and west.


GFS model from Sunday night shows rain over the D.C. area Sunday morning (March 12) but snow as close as northern Maryland.

3. Storm miss scenario (20 percent): In this scenario, the storm passes so far south that we remain dry, but it’s much colder than normal.


Canadian model from Sunday night shows snow staying south of the D.C. area on Sunday, March 12.

Based on these wide-ranging scenarios, our most concise forecast is that a storm will approach the East Coast this weekend that could give us rain, snow or even nothing.

Model discussion

Since Friday, model forecasts have jumped all around with respect to the weekend (March 11-12) forecast.

Last night’s European and this morning’s GFS models offered accumulating snow, while the earlier version of the GFS from last night tracked the storm far enough north to give us rain. Last night’s Canadian model tracked the storm so far south as to leave us dry.

The models are likely to oscillate between snowy and non-snowy solutions over the next couple of days. By Thursday or so, they should start to consolidate and our forecast confidence should begin to increase.

The group of early morning simulations from the GFS model, known as the Global Ensemble Forecast System (GEFS), help illustrate how much uncertainty there still is on the storm track and whether it snows. Remember that ensemble simulations are identical model runs but with slight tweaks to their initial conditions.

Let’s look at their predictions for the positions of the storm low pressure area (indicated by red Ls in the image below) early Sunday.

Forecast positions of storm low pressure on Sunday at 2 a.m. from Global Ensemble Forecast System (GEFS). (WeatherBell.com)
Forecast positions of storm low pressure on Sunday at 2 a.m. from Global Ensemble Forecast System (GEFS). (WeatherBell.com)

They vary from north of Lake Erie to a position over Alabama. Such a large spread suggests that the storm track is likely to continue to jump around in future model runs.

For us to get snow, the low has to track south of us, probably at least as far south as Southern Virginia. A track right over us or to our north would probably produce rain.

Because of the uncertainty of the storm track, the ensembles indicate that the probability of snow is only a little higher than the probability of rain during any three-hour period this weekend.

Probability of different types of precipitation at different times. (NOAA)
Probability of different types of precipitation at different times. (NOAA)
High pressure forecast over Greenland Saturday. (WeatherBell.com) High pressure forecast over Greenland on Saturday. (WeatherBell.com)

The one pattern signal that should give snow lovers hope is that models are predicting an area of high pressure to be centered over Greenland this weekend, reflecting the negative phase of the North Atlantic Oscillation (NAO). When the NAO is negative, the storm track over the eastern United States tends to be forced south, allowing cold air to spill into the Northeast and Mid-Atlantic.

For much of this winter, the NAO has been positive and so storms have passed to our north. Maybe this change to the negative phase will finally deliver for snow lovers.