D.C. area forecast: Disruptive winter storm brings wintry mix tonight, then a cold and snowy Monday

* Winter storm warning tonight into Monday *

11:30 a.m. Update: New model data is streaming in this morning. There are still some inconsistencies from model to model with regard to snow amounts and whether they will be fairly uniform across the area, or if there is a bull’s-eye of snow either over D.C., or a bit to the south along a west-to-east stretch from around Charlottesville to Fredericksburg and into Southern Maryland. We are also assessing where cold air and snow intensity will combine for the highest snow ratios. All this is a fancy way of saying that we don’t expect a ton of change to our forecast, but we may make some tweaks in our next update by around 2 p.m.

8:30 a.m. Update: Overnight, the National Weather Service issued a winter storm warning for the entire area, in effect tonight through Monday afternoon. Part of the warning reads, “VERY HAZARDOUS TRAVEL THIS EVENING TROUGH MONDAY … AFFECTING BOTH THE MONDAY MORNING AND MONDAY AFTERNOON PEAK COMMUTE HOURS. POWER OUTAGES ARE POSSIBLE WITH THE COMBINATION OF ICE AND HEAVY SNOW.”

Our full forecast from 6 a.m. follows below…

Today’s Daily Digit

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

7
Something for everyone, with temps near to above normal for a change, plus anticipation of yet more snow.

Express Forecast

Today: Increasing clouds. Rain showers develop during afternoon. Highs: Upper 40s to mid-50s.

Tonight: Rain turns to wintry mix and then snow. Lows: Upper 20s.

Tomorrow: Snow, heavy at times. Temps: Falling through 20s.

FORECAST IN DETAIL

The calm before the storm is a mild one at least. I use the term “mild” loosely, as what feels mild for us now is actually only near or slightly above average for this time of year. After highs near or past 50 today, a wild weather swing ensues. What begins with a relatively mild rain this afternoon into evening, ends with snow and temperatures diving into the 20s tomorrow, and teens by tomorrow evening!  Nice, huh? After the storm departs, a wicked winter chill makes spring seem like a distant dream.

Today (Sunday): Much of the day should end up dry and not so cold. A mix of sun and clouds is possible during the morning before clouds overtake the region by early afternoon. Most spots should reach the upper 40s to mid-50s for highs, though the far northern suburbs could stall in the mid-40s, while the far southern suburbs may climb close to 60. Rain showers should arrive mid-to-late afternoon from the west-northwest, as winds begin to come from the north. Confidence: Medium-High

Tonight: Temperatures really fall off during the evening with the transition from rain to wintry mix (snow, sleet, rain and freezing rain all possible) starting in our northwest suburbs around 8-10 p.m., and closer to the District by around midnight. By around 5-6 a.m., pretty much everyone should have switched to all snow, except perhaps areas south and east of the Beltway, as temperatures fall below freezing and winds increase from the north. Confidence: Medium

How much snow? Keep reading for the forecast through Monday and into midweek…

Tomorrow (Monday): The storm arrives in full force Monday morning. Any areas holding on to a wintry mix should change to all snow by around 8 a.m. as the deep cold continues to stream into the region. The snow falling on top of a hardening layer of ice should make a mess of the morning commute. The heaviest snow likely falls during the mid-morning to early afternoon, with some areas probably seeing rates of an inch an hour or more, before tapering around 3-6 p.m. from west-northwest to east-southeast. Temperatures continue to crash during the day, falling through the 20s and into the teens by evening, with winds near 10-20 mph from the north. Confidence: Medium

The map below shows our latest accumulation forecast, but is not necessarily our final call. Stay tuned for a full storm update around mid-afternoon…

CWG's snow accumulation forecast, issued 6 a.m. Sunday

CWG’s snow accumulation forecast, issued 6 a.m. Sunday

Tomorrow night: The fresh snowpack makes an ideal situation for overnight cooling. As skies clear during the evening into the overnight, we could be looking at some awfully cold temperatures for March. Overnight lows drop at least into the teens, and some outlying areas could dip into the single digits.  Winds remain from the north, but diminish to below 10 mph. Confidence: Medium-High

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

9 (↑) Hard to see how we don’t get at least a few inches late tonight and tomorrow. Iffy late-week snow chance too.

The storm is long gone by Tuesday, but likely with lingering morning impacts after the overnight deep freeze. Even with plenty of March sun courtesy of high pressure, temperatures by afternoon aren’t likely to get out of the 20s for highs. At least winds are fairly light for those who want to get out and enjoy the late-season snow cover.  Tuesday night, temperatures again tumble to lows in the teens downtown, with single digits possible in the suburbs. Confidence: Medium-High

Wednesday sees partly sunny skies and highs threatening to surpass freezing, most likely maxing out in the low-to-mid 30s. Spring fever anyone? Confidence: Medium-High

Dan Stillman contributed to this forecast

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Update: Significant winter storm Sunday night and Monday