10:35 p.m. update: Since this story was posted in the afternoon, we have no major changes to share. However, we have created an accumulation map (see above) which shows a dusting to two inches is the most likely range for our immediate area, with one to three inches well north and west.
We also thought we’d share this graphic (below) from the National Weather Service which does a nice job communicating the most likely start time for snoq. For the immediate metro area, snow should mostly begin after Tuesday’s p.m. commute, but some light snow is possible in our northern and northwestern areas leading up to and during the afternoon-evening commute – so plan accordingly.
Wednesday morning’s commute is more likely to be affected by snow and some delays and cancellations are possible.
We’ll have more information to share on Tuesday. Have a good night.
Original post from 1:30 p.m.
First things first — we’re not expecting a big snow storm. But we are expecting at least a little bit of snow that will begin late Tuesday afternoon. Overall, this storm looks like a nuisance, and by Wednesday afternoon, it will be more picturesque than disrupting.
We think the chance of at least an inch is about 40 percent.
Light snow is likely to begin late Tuesday afternoon into early evening. It will spread across the D.C. region from west to east, entering the western and northern suburbs in the afternoon and hitting the city between 6 and 8 p.m. The snow should end over the western section early Wednesday morning but could linger into the east of the city. By mid-morning, the snow should be history for most areas.
The most likely scenario is a dusting to 2 inches, with the heaviest snow falling north of the city. These are light accumulations, but because of the cold air and ground temperatures each flake will stick and roads will be slippery.
A boom scenario, one that exceeds our most-likely scenario, would be a widespread 2 or 4 inches. The boom scenario is predicated on the low pressure system developing to our south, and that does not look likely — probably only a 10 or 15 percent chance.
A bust scenario would be no snow to a dusting — about a 10 percent chance.
What the models are saying
The models seem to have come into agreement with the GFS — that the upper-level trough of low pressure is going to be weaker rather than stronger. Also, the surface low development will be too far offshore to tap Atlantic moisture.
Although last night’s European ensembles were unanimous about the area receiving snow, only 30 percent forecast a total over two inches. Monday morning SREF ensembles are on the same page (see below). They are forecasting a dusting to 2.5 inches assuming a 10-to-1 snow-to-liquid ratio. This range or solutions looks reasonable.
Monday morning’s NAM was a Debbie Downer for snow lovers, offering only a dusting to an inch across the city and maybe two toward the Pennsylvania border. The NAM forecast for 1 a.m. Wednesday shows a low developing well offshore too far north to provide us with any heavier snow. The high-resolution NAM is slightly heavier with its precipitation (as usual) and would offer a dusting to three inches with the heaviest being north of the city (see below).
Right now, its forecast looks to be toward the high end of the various possible snow forecast scenarios. The GFS generally forecasts one to two inches across most of the area with its forecast for DCA being right around the mean shown by the SREF output. Like the NAM, it predicts the low to develop too far off the coast and too far north to produce provide any Atlantic moisture.