Important: New link as of 2:00 p.m. Sunday: Revised, detailed D.C. forecast for this snow event

* Winter weather advisory late tonight and Monday except far south burbs (see map) | Winter storm watch for Anne Arundel, Calvert, and St. Mary’s Counties Monday night into Tuesday morning | Winter storm warning tonight and Monday from Winchester to Hagerstown (I-81) and points west *

11:30 a.m. Update: In the immediate D.C. metro area and points east, the snow that falls overnight tonight into the day Monday may not accumulate a lot because of temperatures near to slightly above freezing and a lighter intensity snow (our colder suburbs to the northwest have more potential for disruptive snow tonight into Monday morning).  However, Monday evening, the latest models are advertising a heavier band of snow that may develop as the coastal storm – set to clobber the Northeast coast – cranks up.  That snow would probably develop late in the afternoon and continue through Monday evening, before tapering off early Tuesday morning.  This second phase of the storm (Monday night) is what has the most potential to produce slick roads and challenging travel conditions along the I-95 corridor and points east.

In fact, in our eastern areas from our counties adjacent to the Chesapeake Bay (St. Mary’s, Calvert, and Anne Arundel counties, including Annapolis) northeast to Baltimore, a winter storm watch has been posted for the potential for 3-5 inches of snow Monday night.

Programming note: We will have a new, detailed post on this storm and its effects on the D.C. area at approximately 1:30 p.m.

9:50 a.m. Update: How white will it be when you wake up Monday morning? While we expect at least a coating or so on the grass and possibly sidewalks when you wake up Monday morning, there’s still a chance that roads in the immediate metro area won’t be in terrible condition, since snow tonight is expected to be light with temperatures above freezing through much of the night. As typical, the northern suburbs have the best chance at seeing accumulation on roadways overnight. Even there, treated roads may be in OK shape early in the morning, though areas north of a line from around Leesburg to Gaithersburg to Columbia could be more treacherous with an inch or two on the ground already. Road conditions may deteriorate area-wide during the early-to-mid morning as areas of light snow continue and temperatures drop a bit more. See below for our full forecast…

From 6 a.m. …

TODAY’S DAILY DIGIT
A somewhat subjective rating of the day’s weather, on a scale of 0 to 10.

7/10: Dry through much of the day with highs in the 40s? Equal to or better than your average day this winter.

EXPRESS FORECAST

Today: Increasing clouds. Chance of light rain or snow late. Highs: Mid-40s.
Tonight: Light to moderate snow developing. Lows: Near 30 to low 30s.
Tomorrow: Occasional snow possible. Highs: Near 30 to low 30s.

FORECAST IN DETAIL

Tonight’s clipper system is set to explode into an intense Nor’easter once it moves offshore. The question is, how much snow does it give us before heading up the Northeast coast? A fresh coat of white seems probable tonight into Monday, but that’s not a total lock just yet, and the forecast is full of uncertainties all the way through Monday night. What we do know more confidently is that today should be the warmest we’ll see for a while, with highs stuck in the 30s or lower tomorrow through midweek.


Last night’s NAM model shows an intense Nor’easter Tuesday morning. The question is, how much snow does it give the D.C. area before heading up the coast? (WeatherBell.com)

Today (Sunday): Nobody panic. In fact, there’s little sign of an approaching storm early on, with partly sunny morning skies and highs heading for the relatively warm mid-40s. Still, skies take on a more wintry look as clouds increase late morning into the afternoon. Some light rain or snow showers may try to move in from the west after 4-5 p.m. Confidence: Medium-High

Tonight: Light snow, perhaps mixed with rain, becomes more likely during the evening, but may be focused on the northern half of the area. Also, temperatures through around midnight should be warm enough to prevent much accumulation on roads. After around midnight, though, the snow should become steadier area-wide and should start sticking better as temperatures drop toward freezing. That sets up a potentially dicey morning commute. Confidence: Low-Medium

For related traffic news, check out Dr. Gridlock. Keep reading for the forecast through midweek…

Tomorrow (Monday): Much of the area, except possibly Southern Maryland, probably wakes up to at least a coating to an inch of snow on the ground, unless the initial push of overnight precipitation fizzles out. Early-morning temperatures may still be warm enough such that treated roads are in decent condition. Another inch or two is possible during the day Monday, but that’s only if the storm’s low-pressure center cranks up strong enough and close enough to the coast, which at this point is difficult to say with much confidence. With a steady wind from the north-northeast at 5-15 mph, temperatures don’t do much during the day, staying within a couple degrees of the freezing mark. Confidence: Low

Below is our first-call snow accumulation map for tonight into Monday. It does not include additional snow that may or may not fall late Monday and Monday night. We may also make changes to this map after reviewing this morning’s model data.


First-call snow accumulation forecast for Sunday night into Monday. (Capital Weather Gang)

Tomorrow night: As the storm continues to intensify off the Northeast coast, some models show it throwing even more snow our way, possibly another dusting to an inch or so, especially for eastern and northeastern parts of the area. But at this point that additional snow is far from a sure bet. Colder, drier air begins to stream in as the steady breeze turns more from the north, sending temperatures into the mid-20s. Confidence: Low

A LOOK AHEAD

So Tuesday, yup, more snow showers are possible, but they should be little more than glorified flurries by this point, aside from an isolated heavier burst. The axis of cold air arrives and it leads to a rather brisk day with enough of a breeze from the northwest to be annoying. Skies are still mostly cloudy, and highs should only reach the upper 20s to low 30s. Tuesday night, skies begin to clear just in time for temperatures to drop.  Drop they will, to overnight lows in the mid-teens to near 20. Confidence: Medium

By Wednesday we’re finally precipitation-free! It’s still cold, though. Weak high pressure is strong enough to provide mostly sunny skies. Too bad it won’t really help temperature-wise.  The cold air stays in place with highs once again only in the upper 20s to low 30s. Confidence: Medium

SNOW POTENTIAL INDEX
A daily assessment of the potential for at least 1 inch of snow in the next week, on a 0-10 scale.

7/10 (→): Not yet a lock, but good chance at least parts of the area see an inch or more Sunday night-Monday.

Dan Stillman contributed to this forecast