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Posted at 10:35 PM ET, 03/26/2011

Light snow accumulations from spring storm

Dusting to an inch most likely, more southwest

Winter Weather Advisory for the far south/southwest suburbs


Radar & lightning: Latest regional radar shows movement of precipitation and lightning strikes over past two hours. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

10:35 pm Update: Some of this afternoon’s model data came in slightly snowier that previous runs, but this evening’s model data is scaling back again ever so slightly. The end result is that we don’t see any reason to alter our forecast. With temperatures still having a ways to go to get down to freezing (near 40 at 10 p.m.), and with the snow expected to be mostly light, it’ll be tough to get snow to accumulate any more than the dusting to 1” shown for the metro area in our accumulation map below.

From 2:40 p.m....

Winter weather has decided to stretch itself out into spring and so we now await at least one more opportunity to whiten the ground late tonight through Sunday morning as weak low pressure slides by to our south. For most of the metro region, a dusting to an inch is the most likely accumulation, with up to 2” or more as you head southwest toward Culpeper and Charlottesville. The northern edge of accumulating snow probably sets up somewhere between central Montgomery county and Baltimore.

ACCUMULATION MAP AND TIMELINE

2 AM to 5 AM SUNDAY
Light snow develops SW to E. Temps 29-33.
5 AM to 8 AM SUNDAY
Light snow, moderate south. Temps 27-31.
8 AM to 11 AM SUNDAY
Snow tapers off W to SE. Temps 31-34.
11 AM to 2 PM SUNDAY
Decreasing clouds. Some sun possible. Temps 35-39.

Forecast Confidence: Medium
IMPACT FORECASTS


STORM FAQ

Where is the precipitation now? Follow the progress of the storm on national radar, regional radar and on our Weather Wall.

Will the snow stick? The initial flakes probably melt due to relatively warm ground temperatures and air temperatures right around freezing. As the snow becomes steadier and temperatures fall below freezing, snow will probably accumulate some, first on grassy areas, then side roads and then maybe some main roads, especially to the southwest where snow is more likely to fall moderately. The fact that most of the precipitation will fall before 9 or 10 a.m. when the sun starts to rise will make it easier for snow to accumulate. As the skies brighten and the intensity of snow diminishes, little additional accumulation is likely.

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What does Wes Junker, CWG’s winter weather expert have to say about this storm? Wes - though vacationing in Florida (where he and his buddy reeled in 55 largemouth bass yesterday, including a five pounder) - analyzed the maps and wrote in the following:

“The models continue to indicate the potential for snow late tonight into early tomorrow over the metro area. The temperature profiles are plenty cold enough for snow. But the surface low and upper support are both relatively weak and the track of the low is far enough south to put Washington in the northern edge of the precipitation shield.”

“This morning’s NAM has edged the northern extent of the precipitation a little farther north suggesting there could be up to an inch of snow on grassy surfaces. The mean of all the members of the Short Range Ensemble Forecast System also would give D.C. about 0.10” of liquid which also would support up to an inch of snow, but it also suggests the heaviest precipitation will be south of the area. The GFS model was on the higher side of the range of all solutions giving the area around .20 inches of liquid equivalent which might equate to a couple of inches of snow.”

“My own feeling is that D.C. could get an inch with the southern suburbs possibly seeing and inch or 2 though this late in the season accumulations on the roads can be hard to get. However, only a minor shift in the band to the south could cause the system to miss D.C. completely. One thing the storm has going for it is that the bulk of the precipitation will be falling at night and early morning making the sun less of a factor than if the snow were falling during the day.”

When and where will road conditions be worse? If we do see road accumulation, then the best chance for slick roads would be on side roads between 4 and 9 a.m. Some main roads, particularly untreated ones, could also get a light coating, especially southwest of D.C. where snow may be steadier and/or heavier. After around 9 a.m., the sun (even though masked by clouds) should be strong enough to melt any snow on most roads except maybe the far southwestern suburbs.

Could the storm be more or less than forecast? There’s not a lot of upside to this storm. Even if the precipitation were to track further north than expected, then 2-4” is about the most the metro area could see, but chances of this are low. The bigger risk is that the storm tracks far enough south to leave parts or all of the metro area with no accumulation. Right now, though, it appears that at the very least some areas south/southwest of D.C. are likely to see at least a dusting to half-inch on grass.

What’s the forecast for after the storm? Unfortunately for those searching for spring, the relative cold continues into the coming week. See Ian Livingston’s full forecast.

By and  |  10:35 PM ET, 03/26/2011

Categories:  Forecasts, Winter Storms

 
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