D.C. area forecast: Milder weekend before a significant winter storm threat Sunday night into Monday

10:55 a.m. update: The morning model suite continues to show pretty much what our forecast calls for below, and back up the winter storm watch in effect for the area Sunday night into Monday. Showers push in Sunday evening, quickly changing to a wintry mix overnight Sunday, with snow becoming dominant by early Monday morning. Almost as interesting as the snow potential, the cold air pushing in on Monday appears pretty mean for this time of year. In other words, this doesn’t look like other March storms where we struggle to accumulate because of marginal temperatures. Below, a snow map from the newest GFS as well as a temperature map for midday Monday.

Snowfall forecast from this morning's GFS for the Sunday night into Monday storm system. Note: this is more an estimation than an exact expectation. (Instantweathermaps.com)

Snowfall forecast from this morning’s GFS for the Sunday night into Monday storm system. Note: this is more an estimation than an exact expectation. (Instantweathermaps.com)

1 p.m. temperature forecast for Monday from this morning's GFS. Raw model temperatures often run a little cold, but even adding several degrees or so makes this quite a cold midday. (Weatherbell.com)

1 p.m. temperature forecast for Monday from this morning’s GFS. Raw model temperatures often run a little cold, but even adding several degrees or so makes this quite a cold midday. (Weatherbell.com)

We’ll have a full update this afternoon.

7:30 a.m Update: The National Weather Service – overnight- issued a winter storm watch for the entire metro region late Sunday night through Monday afternoon for a period of freezing rain and sleet, followed by the potential for at least 5 inches of snow. We will have a detailed update on the storm this afternoon.

Today’s Daily Digit

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

7
Warmer than it has been, and tranquil. Main issue might be some periodic cloudiness.

Express Forecast

Today: Partly cloudy, perhaps mostly cloudy p.m. Highs: 42-48.

Tonight: Partly to mostly cloudy. Lows: Near 30 to upper 30s.

Tomorrow: Mostly cloudy, showers and turning colder late. Highs: Near 50 to near 60.

FORECAST IN DETAIL

Temperature Map

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

While we’ve still got almost three weeks until astronomical spring begins, on the meteorological calendar we’ve arrived. Today and much of tomorrow may generally fit the part, but by the time we get through Monday and beyond many may wonder if it’s still January or something. Suggestions of a fairly high impact winter storm continue to grow, with precipitation beginning late Sunday. It runs the gamut from freezing rain to sleet initially, likely ultimately changing to snow across the area. A very (historically?) cold start to the work week as well.

Today (Saturday): It’s another numbing start to the day if you’re up early, but a southerly wind helps mild us up quite nicely compared to yesterday. The trickiest part of the forecast is probably total cloud cover. I’ll call it partly cloudy, but there are hints we end up mostly cloudy at times. There’s an outside shot of a flurry or sprinkle, but I wouldn’t plan on it. Highs head for the mid-40s in general, with a range from about 42-48. Winds from the south blow around 5-8 mph, with some higher gusts. Confidence: Medium-High

Tonight: Skies remain partly to mostly cloudy, and that cloud blanket plus the temporarily warmer flow helps keep our temperatures up. A bit of a respite never hurt anyone, right? Lows dip to near 30 in the usually colder spots, while downtown may stay in the upper 30s or so. Confidence: Medium-High

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

Tomorrow (Sunday): If you’re sick of winter, this might be the day for you, or at least part of the day. Take it in quick though as it won’t last very long. Despite mostly cloudy skies, with perhaps some lengthier breaks, temperatures should “spike” out ahead of the approaching storm and before the cold air crashes in. That means pretty much everyone should head into at least the 50s, with 60 not even out of the question, especially D.C. and south. But while we’re basking in the warmth, cold air is on the move south. Precipitation may begin advancing into the area by evening (40% chance), mostly in the form of a few rain showers, and maybe focused north and west. Confidence: Medium

Tomorrow night: Rain showers transition to freezing rain and sleet (70% chance), with freezing rain probably not lasting too long, and a more extended period of sleet possible into the night. As we get past midnight and toward sunrise, the wintry mix should transition toward snow, especially I-95 and northwest. The whole area wants to flip over to snow in the hours around sunrise. Temperatures are near their warmest overnight, but fall off to the upper 20s to around freezing by sunrise. Confidence: Low-Medium

A LOOK AHEAD

Snow Potential Index

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

6 (↑) Potentially significant winter storm increasingly likely Sun night into Mon. Still some questions to resolve.

As we start Monday off, some wintry mix may still be around, but the general story should be an increasingly snowy one through the morning and into the midday. Snow may come down moderately to heavily at times across the area, with at least several inches possible most spots. The lowest totals are likely to focus south and east of D.C., but even those places could end up with enough to shovel. The other big story will be plummeting temperatures. We see highs around midnight, with temperatures falling to near 30 by sunrise, and well into the 20s as the day goes. Winds could also be quite gusty from the north as Arctic air pours in. Snow should wind down by late afternoon or evening. Confidence: Low-Medium

With clearing skies Monday night, Tuesday morning lows may be about as cold as we’ve seen all winter, and could test all-time March numbers with some north and west suburbs close to or below zero and downtown in the single digits to around 10. Add in a gusty wind from the north and it could be pretty brutal early in the day. And it won’t get much better as the sun goes to work. Despite mostly sunny skies, highs should struggle to get much past the mid-20s, maybe upper 20s to around 30 in the warmest scenario. Confidence: Medium

We’ll have a detailed update on the winter storm sometime this afternoon.

Post initially prepared overnight

Correction: The post originally published at 5 a.m. had an erroneous headline indicate the winter storm would occur Monday night into Tuesday, instead of Sunday night into Monday.

Also on Capital Weather Gang

PM Update: Not as cold this weekend as we await next winter storm