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Posted at 01:30 PM ET, 01/25/2013

Washington D.C. braces for Friday PM rush hour snow event (LIVE BLOG)

* Winter Weather Advisory from 2 to 9 p.m. today | Schools to dismiss early ahead of expected snow | Snow could snarl PM commute | The Weekend and Beyond: Snow, Metro work and more*

2:00 p.m. update: This live blog has concluded. We’ve started a new live blog here: Snow rapidly moving into Washington, D.C. area for PM commute (LIVE BLOG)

1:30 p.m. update: Snow continues in northern Maryland, the eastern panhandle of West Virginia, northwest Virginia and is advancing northeast through central Virginia. We are getting reports of snow around Front Royal and Charlottesville in Va as well as in parts of Madison and Spotsylvania counties. In Maryland, snow has reached Frederick and Westminster.

Light snow is likely to break out in Washington, D.C.’s far western suburbs in the next 30 minutes or so - mainly Loudoun and Fauquier counties.


Radar image as of 12:30 p.m. Friday. See explanation below why it is not a real snow hole.

1:00 p.m. update: Is that really a snow hole forming over Washington, D.C.? See above image.

Not really.

A good amount of the precipitation you see to the east and southeast of D.C. is not actually snow reaching the ground, but is something called virga, which is snow that evaporates in the air because it is very dry. Radar is picking it up because the beam increases with height in the atmosphere away from its location near Dulles Airport.

As it turns out, snow is falling but not reaching the ground at high altitudes around D.C. too, but the radar isn’t sensing it because it only picks up precipitation closer to the ground near the radar site. Once the atmosphere gets moister and snow actually gets close to the ground, the hole will fill. We see this “snow hole”-like appearance in the run-up to most storms, but it’s not real.


Friday snow potential forecast, second call. Initially posted at 11 p.m. 1/24.
Overview:Areas of light to occasionally moderate snow are likely, starting around mid-afternoon in the region, lasting through the P.M. commute. The most likely start time is between 1 and 4 p.m., starting first in western areas. Snow will taper off between 6 and 9 p.m.

The snow will move through rather quickly, but will coincide with the afternoon and evening commute. Slick travel and reduced visibilities are possible. This is not a crippling storm but our advice is to allow extra time and/or leave work/school early.

Snow amounts should vary between about 0.5 to 2 inches of powdery snow throughout the region.

Sunny, but cold weather returns for the weekend. See Camden Walker’s forecast for additional details.

Previous updates


Simulated precipitation from NOAA’s Rapid Refresh Model

12:30 p.m. update: Light snow has now started as close as Frederick, Md, but radar shows little activity immediately west of the D.C. area. Precipitation is having some trouble making it over the mountains, as expected. Our projected start time for snow in the metro area is between 1 and 3:30 p.m. from northwest to east based on model data and radar trends.


11:55 a.m. update: In the western half of Maryland, traffic cameras show steady snow falling along I-68. Twitter follower @todderdj indicates ”spitting” light snow as far east as Mt. Airy. A Facebook reader notes flurries in Hagerstown.

11:45 a.m. update: Radar shows light to moderate snow developing well west, southwest, and northwest of the region - mainly in the eastern panhandle of West Virginia, the western half of Maryland and in central Virginia. Look for this activity to advance eastward and reach D.C.’s far western suburbs by around 1 p.m.

11:20 a.m. update: While we’re getting worked up over 0.5-2” of possible snow, consider on this date in 2000, D.C. was hit by a surprise snowstorm which dumped up to 12-15 inches.

11:10 a.m. update: The National Weather Service posted the following summary information in its forecast discussion for the D.C. area which I generally agree with:

SNOW DEVELOPS BETWEEN 2 TO 3 PM AND WILL BE STEADY BY 4 PM. VISIBILITIES OF 1/2 MILE IN MODERATE SNOW WILL CREATE HAZARDOUS TRAVELING CONDITIONS FOR THE AFTERNOON COMMUTE. TEMPERATURES IN THE 20S MEAN ANY SNOW WILL QUICKLY ACCUMULATE ON THE ROADS.

I would only qualify that due to the patchy nature of the snow coming, not everyone will necessarily experience conditions this bad.

10:50 a.m. update: Multiple school systems throughout the region are closing 1 to 2.5 hours early today in anticipation of snow this afternoon and evening. Fairfax and Prince George’s counties are closing 2 hours early, and Montgomery County 2.5 hours early. Loudoun county schools are closing 1 hour early. Follow our Twitter feed to see other early closing information.

By  |  01:30 PM ET, 01/25/2013

 
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