* Winter weather advisory 9 p.m. Tuesday to 9 a.m. Wednesday | SchoolCast and FedCast *

A weather system zipping toward the East Coast will brush the region with snow tonight and could cause some slippery travel through Wednesday morning’s commute. Some delays are possible, but the worst conditions will be a good deal to the north and south of the D.C. region.

Around the District, this is more likely to be a sweep-able snow (with a broom) than a shovel-able snow with a dusting to an inch or two expected.

Timing

Some spotty light snow could begin in our far northwest areas, toward Frederick, Hagerstown and northwestern Loudoun County late this afternoon and early this evening, but should hold off until after the commute near the District (within a one- to two-county radius).

Most likely, the snow begins between about 8 p.m. Tuesday and 1 a.m. Wednesday from northwest to southeast. Inside the Beltway, the most likely onset is between 9 p.m. and midnight, when a winter weather advisory takes effect.


High resolution NAM model simulated radar from Tuesday afternoon to Wednesday evening. Note that sometimes this model is a little fast in developing precipitation and we think snow could start an hour or two later than portrayed here.

The snow should exit the region rapidly between 4 a.m. and 10 a.m. from northwest to southeast. Inside the Beltway, the snow should be over just as Wednesday’s commute is beginning, between about 5 and 8 a.m.

Amounts

Washington finds itself in a bit of a snow hole for this event, with the heaviest amounts likely to fall to the north and south.

Our official forecast is for a dusting to two inches, but the latest model information suggests 0.5 to one inch is more likely than two.

In northern Maryland, in the mountains to our west, and down toward central Virginia, one to three inches of snow is possible.

Impacts

Because of the recent cold weather, snow that falls should stick — which means untreated roads will become slippery. And the snow will be ending as Wednesday’s commute is beginning, which will likely result in some delays.

Cold air spilling into the region behind the front coming through will allow the snow to remain on the ground into Thursday (although in places where just a dusting occurs, the snow could evaporate in sunny areas Wednesday afternoon).

But the snow amounts and intensity should be light and the duration of the event short, preventing it from becoming too disruptive. We rate the event a Level One “nuisance event” on our 1-5 winter storm impact scale for the entire region.

Discussion

This is a light snow event that is hard to get too excited or worried about. Essentially, the snow is being produced by a cold front which will be running out of moisture as it approaches the region.

A new storm will form off the Jersey Shore as the front reaches the coast, resulting in big snows from the Poconos to Massachusetts, but Washington will be too far south to draw in any moisture from the coastal storm. That’s the reason this is more likely to be a nuisance event than a more significant one locally.

In the Washington region, the heaviest accumulations are expected in our northwest areas, where the snow will start earlier and where the front has the best chance of maintaining its oomph before fizzling. A bust scenario could play out throughout the region if the storm to our northeast forms too fast, which would draw in winds from the northwest, drying out the air.

In a cruel twist for local snow lovers, Washington will not only be too far south to get moisture from the coastal storm but also too far north to capitalize on some enhanced snow produced by the upper-level disturbance passing through southwest Virginia.

In other words, Hagerstown and Harrisburg, Richmond and Raleigh are likely to see more snow than Washington.


National Weather Service snowfall forecast through Wednesday night. (WeatherBell.com)

Right now it’s hard to envision a boom scenario of two to four inches around the city and three to five toward the Mason-Dixon Line. The one way that could happen would be for a smaller-scale band of heavier snow to develop that the models missed.