D.C. area forecast: Enjoy today because Sunday brings a wintry wallop

December 7, 2013
GFS precipitation type forecast for 1 p.m. Sunday as of this morning's run. (Weatherbell.com)
GFS precipitation type forecast for 1 p.m. Sunday as of this morning’s run. Blue is snow, orange and pink are various forms of ice. (Weatherbell.com)

10:50 a.m. update: With several of the models in from this morning, it appears any modifications to the forecast for the storm should be relatively minor. The North American Mesoscale model (NAM) brings precipitation in on the early side of indicated below, and flips from snow on the early side as well — by around 1 p.m. in D.C. The Global Forecast System (GFS) — probably favored as part of a blend — is basically on track with the ideas we’ve been giving below and yesterday. It would indicate snow changing to sleet and freezing rain around 2 p.m. in D.C. and a little later further north. All indications continue to point to the region staying near and below freezing through the day Sunday and into the overnight, with some warming possible late.

We’ll have an in-depth new post, including a fresh timeline and storm FAQs, by 2 p.m.

Today’s Daily Digit

A somewhat subjective rating of the day’s weather, on a scale of 1 to 10.

5
We may salvage a relatively decent afternoon, but it’s chilly and breezy enough not to go higher.

Express Forecast

Today: Clearing, becoming partly cloudy. Breezy. Highs: 39-45.

Tonight: Increasing clouds. Slight chance of snow around sunrise. Lows: 23-30.

Tomorrow: Snow becoming likely in the morning, changing to sleet and freezing rain. Highs: Near 30 to near freezing.

FORECAST IN DETAIL

Temperature Map

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

From 5:00 a.m.: Today’s calm before the storm might not be totally calm thanks to some wind. Tomorrow is looking ugly — a day to park yourself indoors if you can. While preparing for what’s to come, bundle up a bit and spend some time outdoors today. Cabin fever might be right around the corner — at least for some spots — especially out west of the urban corridor.

Today (Saturday): Last night’s rain is off to the east, but I can’t rule out an early shower mainly east of the city. Otherwise, skies trend clearer as the day progresses. Highs range from near 40 to the mid-40s, perhaps grouping a little more tightly than that. North winds around 10 mph may be gusty at times. Winds pump in lower dew points as well. Those’ll help us cool a bit extra as precipitation arrives on Sunday. Confidence: Medium-High

Tonight: Skies could start off partly to mostly clear, and when you couple that with the lower dew points we should have no trouble getting temperatures to head rapidly through the 30s early on. Getting past midnight, thicker clouds should make their advance back on the region. Despite the blanket, we’ll still end up seeing most spots make it into the 20s — 23-29 or so (downtown 30?). Slight chance we see snow into southern parts of the area around sunrise, but it should want to hold off until daylight. Confidence: Medium-High

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

Snow Potential Index

A daily assessment of the potential for at least ~1″ of snow in the next week, on a 0-10 scale.

7 (↑) Ice still biggest risk Sun-Mon, but start of storm has a snow accumulation window. Tues also worth watching.

Tomorrow (Sunday): Precipitation, largely in the form of snow to start, is on its way in from the south/southwest as we get toward 8-10 a.m. or thereabouts. Our “snow window” could be as brief as until about 1 p.m. in D.C., but it could also continue a little deeper into the afternoon and lasts longest north. Depending on the way the initial bands arrive, our most likely snowfall ranges seem to be as little as about 0.5″ snow to as much as 2″ or so. Warmer air aloft can’t be held back though, and we ultimately all flip to sleet and freezing rain during the late day. Daytime highs are only in the near 30 to near freezing range, and that could could mean 20s after precipitation begins, or during the heaviest, especially northwest of I-95. Confidence: Medium


Snow forecast issued Dec. 6 at 3 p.m.

Tomorrow night: It’s still uncertain exactly how quick we’ll warm up. In short, the further northwest of I-95 you are, the better your shot to stay with frozen precipitation the longest. Temperatures may rise just above freezing in D.C. and to the southeast as early as mid-to-late evening, but perhaps midnight or later. As you get further north and west, it could be tricky until the sun comes up on Monday thanks to temperatures idling in the upper 20s to lower 30s range. A sleet mix may continue into the evening, and lighter activity (showers and drizzle) is also possible prior to a “second wave” after midnight.

Travel is likely to be impacted and is probably not advised in areas that remain below freezing into the night. There could also be a growing risk of damage to trees and power outages. Charge those devices just in case. Confidence: Low-Medium


Ice forecast issued at 3 p.m. Dec. 6.

Related: Yesterday’s in-depth look at the storm (little change since)

A LOOK AHEAD

Icing may still be a problem early over western parts of the area on Monday, but everyone should rise above freezing as we get into the hours beyond sunrise. Unfortunately, the conveyer belt seems to want to keep on coming, so rain showers are a good bet through at least the afternoon. Models are suggesting temps reach the low-to-mid 40s, but I’d hedge a little given that parts of the area might still be caked in ice, plus the fact there’s no strong surface winds from the south. Let’s say upper 30s to low 40s for highs. Maybe some sun late? Confidence: Low-Medium

As weird as it is these days to even have wintry weather in winter around here, we need to watch the potential for more by Tuesday. A fairly active moisture feed tries to keep on coming as cold air settles in to the region. That could be a recipe for at least some light snow (maybe rain) across the area. Under a scenario where that happens, highs are held in the 30s. Should it not come together and slide off to our east, highs closer to 40 probably. It’s perhaps 50/50 that we see even light precipitation for now, but there have been some hints at more than that.  Confidence: Low-Medium

Programming note: We’ll have an update on the storm somewhere in the lunchtime to early afternoon period, and earlier if necessary.

Ian Livingston is a forecaster/photographer and information lead for the Capital Weather Gang. By day, Ian is a defense and national security researcher at a D.C. think tank.
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David Streit · December 7, 2013