11:00 p.m. update: The afternoon and evening models are interesting. Collectively, they tend to favor this kind of scenario: It gets very mild Sunday, while into the 50s to even near 60. Rain moves in Sunday night but – as temperatures crash – switches over to an icy mix and then snow before or by around dawn. Then they suggest the potential for several inches of snow Monday.
The critical element in the forecast is the speed at which the cold air arrives. If it’s a fast arrival, this is a major winter storm for much of the metro area. If it’s slower, then the impact lessens – especially from the District and points south and southeast.
Here’s a nice explainer graphic from the National Weather Service forecast office in Sterling, Va.:
And here’s a dramatic sequence showing the NAM model’s temperature forecast between 4 p.m. Sunday and 7 a.m. Monday – the temperature in D.C. falls from 62 to 22 degrees in 15 hours!
Much more tomorrow…
From 4:30 p.m.: Highs mainly in the upper 20s today didn’t set any cold-weather records, but were a good 20+ degrees below average. The cold eases Saturday and especially Sunday, as the weather stays mostly quiet through much of the weekend. It all goes downhill late Sunday, however, as precipitation chances increase and cold air makes a comeback from the north. That leads into what could be a messy start to the work week come Monday morning.
Through Tonight: We’re mostly clear into the evening, and really just too cold for comfort, though we’re not headed as low as last night. Overnight lows bottom in the teens to low 20s with some increasing clouds late. Winds stay light.
The Weekend: After another cold start Saturday morning, partly sunny skies and light winds from the south help temperatures recover decently by afternoon. Highs reach the low-to-mid 40s, maybe even solidly into the mid-40s, with perhaps a stray flurry or sprinkle. Skies stay partly cloudy through a not-as-cold Saturday night with lows in the 30s. Sunday sees building clouds with a 40% chance of rain showers by late afternoon. Highs should reach at least the upper 40s, if not into the 50s.
Sunday Night-Monday Mess: Rain chances hold around 50% through Sunday evening. Colder air sinks in from the north overnight, potentially turning any rain into a wintry mix as precipitation chances increase to the likely range. Monday is a good bet to be a messy day with a variety of precipitation types early (rain, sleet, snow, and freezing rain all possible), perhaps changing to mostly snow for at least parts of the area, especially north and west of D.C. It’s another chilly one, too, with early highs in the 30s likely falling toward or into the 20s.
See this post for a more detailed look at what we expect late Sunday through Monday.