Update, 10:45 a.m.: We’ve seen the latest GFS model and it’s consistent with our increased snow expectations for Tuesday’s storm.  A general 3-6″ across the area seems like a good bet with locally higher or lower amounts not out of the question, but we’re still analyzing everything and discussing. Stay tuned for the afternoon update.

Update, 9:30 a.m.: Looking at the latest data coming in, our snow expectations have risen some and think most of the area has a good chance of 4″ or even more Tuesday. Our midday to afternoon update will have more details.

Update, 7:30 a.m.: The National Weather Service has issued a Winter Storm Watch Tuesday for the entire region, meaning the potential for 5 or more inches of snow. It doesn’t mean this amount of snow is guaranteed, but there is at least a 50 percent chance of this much. We think this amount of snow is possible in a heavy band somewhere in the region, but it’s not yet clear the entire region would see this much snow. This is a low-end watch event, meaning the National Weather Service sees 5″ at the high end of the likely range. We agree that the watch is warranted. We’ll have updated information in the midday to early afternoon period, after reviewing some new information coming in.

FORECAST IN DETAIL

Temperature Map

Temperatures: Latest D.C. area temperature map. See interactive map on our Weather Wall.

Enjoy today as one of the more severe periods of winter weather in the last few years then grips the region.  It starts Tuesday with the likelihood of accumulating snow, complemented by plunging temperatures and eventually punishing winds. Wednesday through Friday it’s downright cold, before modest increases in temperatures by the weekend.

Today (Monday): This is perhaps the last day for a while you won’t be uncomfortable without a scarf and hat.  By early-to-mid afternoon, we reach highs around 50 and winds are mostly light, from the west at around 10 mph. Towards late afternoon, an arctic front moves into the area, but we don’t really start to feel its effects until overnight. Confidence: Medium-High

Tonight: Becoming mostly cloudy, and gradually colder – from northwest to southeast.  There’s a 20-40 percent chance of snow by around sunrise (highest chances in western areas), with lows from the mid-20s in the colder suburbs (west and north) to around 30 downtown and east. Yes, the early part of the rush hour could see snow starting to fall, especially in western areas. Confidence: Medium

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

Tomorrow (Tuesday): Snow is likely, developing rapidly west to east between 7 and 10 a.m. (if not a bit earlier). Temperatures gradually fall through the 20s.  By evening, colder suburbs north and west of the District could be in the high teens, with lows 20s closer to town.

Snow accumulation of at least an inch or two is a good bet, with higher amounts (of 4 inches or more)  a possibility in a narrow zone to be determined.  There is likely to be a sharp cutoff between lighter snows and heavier snows. We’ll issue a detailed snowfall forecast this afternoon.

Winds from the north at around 10 mph in the morning increase to 15-20 mph in the late afternoon, with higher gusts.  Some blowing snow and reduced visibilities are possible, and could make for a hazardous p.m. commute. Confidence: Medium

National Weather Service in Sterling is calling for 2-4 inches of snow over the region Tuesday, which is a reasonable first forecast. (National Weather Service)

Tomorrow night: Snow tapers off in the evening, with clearing skies but it’s windy and extremely cold. Some blowing snow is possible (after the snow ends), especially in rural open areas.  Lows range from 0 to 10 degrees (suburbs to city), with sub-zero wind chills. Winds are from the northwest at 10-20 mph, with gusts to 30 mph or so.  Confidence: Medium

A LOOK AHEAD

Winds slowly subside Wednesday, with brilliant sunshine. But the cold is bone-chilling, with highs only from the highs teens to low 20s. Mostly clear and frigid Wednesday night, with lows from around 3 to 13 (downtown). Confidence: Medium-High

A weak disturbance and reinforcing shot of cold air scoots through the area Thursday.  A few snow flurries or snow showers can’t be ruled out (no big deal in all likelihood), with highs in the mid-to-upper 20s and increasing winds in the afternoon. Windy and extremely cold Thursday night, with lows in the single digits to low teens and sub-zero wind chills. Confidence: Medium

Partly to mostly sunny and cold Friday, with highs 25-30. Partly cloudy Friday night and not quite as cold, with lows 17-25 (suburbs-city)  Confidence: Medium

The weekend is cold, but we have a fighting chance to best freezing both days, more likely Saturday.  Another arctic front crosses the region, probably late Saturday, so Sunday could see a step back in temperatures.  Right now, I’ll play it open-ended and call for highs in the 30s both days and lows Saturday night in the 20s.  I can’t rule out a chance of snow or mixed precipitation perhaps late Saturday…but details are really fuzzy. Confidence: Low-Medium