GFS model shows snow over the D.C. area Saturday morning into the afternoon.

The Washington area is on the edge of a coastal storm system that could sideswipe it with wet snow Friday night into Saturday. But if the system tracks closer to or farther from the coast, it could mean more significant snow or no snow at all.

The westward edge of this coastal system has been a moving target for days. Since Wednesday night, the edge has moved into the D.C. area, somewhat increasing snow chances.

Based on the latest information, we lean slightly toward the immediate D.C. area seeing mostly conversational snow at times Friday night and Saturday (a few flurries or sprinkles could break out as early as Friday afternoon). By conversational, we mean flakes in the air but having trouble sticking. Snow might accumulate a coating to an inch, mostly on grassy surfaces — if the latest models are correct.

We are, for the first time, introducing our Snow Lover’s Crystal Ball, signaling at least a 30 percent chance of an inch or more of snow in the immediate metro area. In this instance, the chance is right at 30 percent between Friday night and Saturday afternoon, given the uncertainty about both available moisture and temperatures.

Locally, higher amounts exceeding an inch are possible in any of the small bands of heavier snow, most likely occurring east and southeast of Washington on Saturday. In these heavier bands, we cannot rule out pockets of slick road conditions. The most likely period of any steadier snow would be Saturday morning.

Ground and air temperatures — hovering in the low to mid-30s — are likely to be too warm for more significant accumulation unless the system comes a little closer and snow falls at a steady clip. Then temperatures would fall, and a few inches would be possible.

On the flip side, if the track shifts east farther offshore, the D.C. area probably escapes seeing much, if any, snow except for our far-southern and eastern suburbs.

Unlike the case with many winter weather events that affect the region, locations from Leesburg to Frederick and to the north and west are likely to see the least snow, as they will be farthest from the moisture source, the Atlantic Ocean. However, if the system shifts farther west, snow would accumulate in such locations more readily because of colder temperatures.

Because the forecast is shifting around so much, we want to wait until tomorrow to issue any accumulation maps, nail down the timing, and assess the likely impact of this system. Continue to monitor our updates, especially if you have travel plans on Saturday.

Unfortunately, this is the kind of winter weather system that is the hardest to forecast and most likely to result in surprises — with either more snow than expected or nothing at all.

Model discussion

Today’s European, American (GFS) and NAM models shifted the system closer to the coast, compared with last night and, therefore, jumped the precipitation shield north and west, giving the area wet snow.

All the models still show the heaviest precipitation and highest snow potential east and southeast of Washington.


GFS model snowfall forecast through 7 p.m. Saturday. Note that some — maybe more than half of the snow shown in this model — would probably melt before accumulating.

If all of the snow simulated by these models were to stick, we would be looking at one to three inches — mostly along and east of Interstate 95.

Throughout the region, the temperature is likely to be between 33 and 35 degrees, meaning some — if not most — of the snow will melt. If the snow falls steadily, though, these temperatures would probably fall to 31 or 32, and the snow would stick more readily.


European model forecast of temperatures at 10 a.m. Saturday. (StormVistaWxModels.com)

Of the simulations of the American model, many — but not all — now show accumulation. Note, however, that these snowfall forecasts assume all of the snow sticks, which will not be the case. Also notice that there are simulations that show no snow.


Snow forecasts from the various simulations of the GFS model with input day tweaked. (WeatherBell.com)

Two factors, which forecasters will need to closely watch, will have significant implications for how much snow falls. They are:

  1. How much does dry air on the system’s northwest periphery eat into potential snowfall? This is the type of event where radar might detect snow falling from the sky, but the snow will evaporate before reaching the ground (this is known as virga) in some areas.
  2. Will a narrow band of heavy snow develop on the northwest periphery on the boundary where the dry air stops and the moist air starts? This happens in some events like this, and some locations in D.C. area could fall into this zone.

Stay tuned.