The latest model data indicate a period of wet snow occurring during the afternoon of Christmas Eve into the evening. In high elevations of Loudoun and Frederick county, enough snow may fall for a White Christmas and even some of D.C.’s north and west suburbs could pick up a sloppy accumulation on grassy areas. South and east of town into southern Maryland and near the Chesapeake Bay, a mix of rain and snow is more likely and little or no accumulation is expected.
Timing: Between noon and midnight, starting first to the southwest and ending last to the northeast
Accumulations: 1-2 inch or so above 1,000 feet in Frederick and Loudoun county; a coating to 1 inch or so north and west of the beltway mainly on grassy areas; no accumulation to 0.5 inch inside the beltway; no accumulation to coating or so south and east of the beltway
Temperatures: When snow starts Monday afternoon, temperatures will generally be above freezing, in the mid-to-upper 30s. Precipitation may even begin as rain before mixing with and changing to snow. Late afternoon and early evening, temperatures will dip into the low-to-mid 30s (coldest north and west of the beltway; warmest in town and south and east)
Impacts: This is generally a low impact event as snow will have difficulty sticking to road surfaces except at higher elevations; however, there could be a period of moderate snow which lowers visibility and generates a bit of roadway slush late afternoon into early evening. Once any snow ends, the risk of significant re-freezing overnight is low as temperatures hold steady and precipitation may even end as drizzle (except at higher elevations).
What’s Wes Junker’s, CWG’s winter weather expert, view? Junker agreed the NAM model suggests mostly snow around the D.C. area, with best accumulation chances towards Loudoun and Frederick counties, and noted the model had been trending colder today.
Could this forecast go wrong? Yes. If temperatures are a bit warmer than modeled or precipitation lighter than modeled, this could turn into just a cold rain. Temperatures are barely cold enough to support snow, so margin of error is low. I’d say if this forecast is wrong, it’s more likely to err on the side of being too snowy (i.e. we end up with mostly rain) rather than not snowy enough.
Please stay tuned for more details Monday morning.