6:30 p.m. update: Temperatures are slowly and steadily falling. Most places are at or below freezing (some spots from D.C. S & E a degree or two above). Dew points are very low, around 10 degrees. This is an indication of very dry air. Although regional radar (snowing heavily in Chicago) shows precipitation very close to the area into northern Maryland and eastern West Virginia, it is evaporating before reaching the ground.
Over the next several hours, the atmosphere will moisten and temperatures will gradually fall. Besides a few flurries, don’t expect meaningful frozen precipitation until 10 p.m. or later (after midnight a better bet).
Our forecast below (and in earlier updates today) is unchanged, although we may see a little less snow and a bit more ice; something few probably want to hear...
Forecast summary, posted at 4 p.m.: Winter weather advisories have been posted and our detailed timeline, accumulation map and zone forecasts for this storm are out. Now we just await the first flakes and/or pings of sleet, likely to move in between 10 p.m. and 2 a.m. tonight. Around 1” of snow and sleet is possible around the metro region tonight, followed by freezing rain. Saturday morning, freezing rain may transition to rain, especially from the District and to the south and east as the morning wears on. Elsewhere, it remains an icy mess into the early afternoon.
Through Tonight: Skies are cloudy this evening and locations not already below freezing, all drop below 32. We may begin to see precipitation on radar in fairly short order, but, because the atmosphere is so dry, much of it evaporates before reaching the ground early on. Some time after 10 p.m. (new models are trending a little later with the onset time), snow and/or sleet will develop from southwest to northeast. By 1-2 a.m., most spots should have frozen precipitation falling.
After a brief period of snow/sleet (1” or so of accumulation possible), precipitation transitions to freezing rain later at night from south to north. Lows range from 24-30 (northwest to southeast)
Both roads and sidewalks may be very slick late at night and in the morning. Use caution driving and walking.
Saturday: Freezing rain (possibly sleet north of D.C.) is likely in the morning, possibly changing to rain from the beltway region to the south and east as the morning wears on. To the north and northwest of the beltway, temperatures probably remain at or below freezing into the early afternoon, so continued icing is possible. Precipitation gradually tapers to drizzle or freezing drizzle during the early-to-mid afternoon. Highs range from near freezing north and west to the upper 30s south and east.
Saturday night and Sunday: Temperature drop back below freezing everywhere Saturday night, so watch out for a re-freeze and slick spots. Skies are mostly cloudy, with lows 25-30 (suburbs-city). On Sunday, it remains cloudy and raw. During the afternoon, some light drizzle or freezing drizzle north and west of the District return may return (40% chance). Highs are only in the mid-to-upper 30s.
Weather -related closings: The Buzz says some schools have pre-emptively canceled Saturday activities ahead of the storm, including Charles and Anne Arundel counties. Expect more to follow...