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Posted at 11:00 AM ET, 02/20/2008

Update: Light Snowfall Still On Track

By Matt Ross

Another storm could bring late-week wintry mix

**Snow Advisory in effect for metro area from 11 a.m. to 10 p.m. today**

Snow is on schedule to move into the DC area from west to east during the next few hours, and is expected to continue through the afternoon, ending by early evening. With temperatures holding mainly in the low 30s, accumulations of a dusting to 1" are likely across the DC area. Some places could receive a little bit more, up to about 2", especially if snow becomes moderate to heavy at times. Downtown, slightly warmer temperatures may limit accumulation on paved surfaces.

While no ice is forecast to fall from this storm, slick spots and poor traction are a concern for the commute home. Check back this afternoon for our CommuteCast.

See Dan's post for the forecast for tonight's lunar eclipse and through the weekend, including a chance for an accumulating wintry mix Thursday night into early Saturday. For additional details on the late-week wintry weather, see the Snow Lover's Crystal Ball below.

Next Chance of Accumulating Snow: Thursday Night through Saturday Morning
Probability: 50%
Potential Impact:

With a cold air mass in place, a complex storm system involving two areas of low pressure will approach from the south and southwest late Thursday. The storm may come in two separate waves of precipitation with a lull in between. While precipitation may start out as snow for much of the metro area Thursday night, a variety of precipitation will likely fall across the region by the time the storm exits, probably by early Saturday.

This is a much trickier storm to forecast than today's. Here's our best guess on timing and accumulation potential ...

Light to moderate snow could spread over the area Thursday night, lasting into the morning with some accumulation possible. During the day on Friday, as warmer air moves in from the south at the upper levels of the atmosphere while cold air holds strong at the surface, sleet and freezing rain will likely begin to mix in with the snow from southeast to northwest.

It's too early to pinpoint the timing and extent of the changeover in precipitation, but there is potential for significant snow and/or ice accumulations in areas that remain at or below freezing at the surface. Precipitation should taper by late Friday evening into early Saturday morning.

While this storm may not bring major amounts of snow, it is still a tricky, long-duration event that could have a moderate impact on the region, especially in areas that experience freezing rain. Total accumulations on the order of a few inches are certainly possible. And there's the potential for several inches if the timing of changeover from snow to ice takes longer than currently anticipated.

By Matt Ross  | February 20, 2008; 11:00 AM ET
Categories:  Updates, Winter Storms  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Forecast: Winter Puts on Its Rally Cap
Next: Lessons Learned: Road Crews Prepped and Ready?


The 15z RUC shows most precip getting ringed out in the Allegheny Front - a sliver of precip finds it way into northern Lodoun and a little west and north into Washington counties. Some verga showing up in the metro area right now. All depends of course on where the low tracks, a little more south than indicated now and the "sliver" could end up inside the Beltway. But what about temps?

Posted by: Nader | February 20, 2008 11:16 AM | Report abuse

Looks like northern and western burbs will do best..but most of us will see a 3-5 hr burst of snow this afternoon...sticking will be an issue some places, but at least we will see flakes.....the late week storm is more promising for snow lovers

Posted by: Matt Ross, Capital Weather Gang | February 20, 2008 11:28 AM | Report abuse

I'll put 20 on a disappointing flurry shower, 40 on my neighborhood Super Target being sold out of water over this, and all on Roche giving me a 5 minute long traffic report since all of DC's roads will shut down over a couple of flakes of snow.

Posted by: Mason Patriot | February 20, 2008 11:53 AM | Report abuse

A few flakes fluttering down in Gaithersburg

Posted by: natsrgreat | February 20, 2008 12:14 PM | Report abuse

flakes in Tysons too

Posted by: Anonymous | February 20, 2008 12:16 PM | Report abuse

Very light snow/flurries in Ellicott City.

Posted by: IanK | February 20, 2008 12:16 PM | Report abuse

flakes in downtown

Posted by: cohnj | February 20, 2008 12:18 PM | Report abuse

Temps have dropped from 34F to 31F here in the last 45 minutes. Something is happening up there but nothing to show for it so far.

Posted by: arnoldkh | February 20, 2008 12:18 PM | Report abuse

I see snow here in Arlington. Just a few large flakes :)

Posted by: snowlover2! | February 20, 2008 12:18 PM | Report abuse

Flurries at Union Station.

Posted by: dixie | February 20, 2008 12:26 PM | Report abuse

Flurries in Scott Circle :)

Posted by: Nader | February 20, 2008 12:27 PM | Report abuse

A few flurries on the Herndon/Reston line :) ...hopefully more to come :)

Posted by: Jenn in Reston | February 20, 2008 12:28 PM | Report abuse

flakes at farragut west

Posted by: Anonymous | February 20, 2008 12:32 PM | Report abuse

Flurries here

Posted by: Bailey's Xroads | February 20, 2008 12:33 PM | Report abuse

Light snow in Annapolis!

Posted by: Larry | February 20, 2008 1:02 PM | Report abuse

A few commenters have asked previously how to find the site. There are a few different routes, but the easiest to remember is

Posted by: Capital Weather Gang | February 20, 2008 1:02 PM | Report abuse

Light snow here in Arnold, temp has fallen to 29F.

Posted by: arnoldkh | February 20, 2008 1:11 PM | Report abuse

30 second burst here at Gallows Rd and 29 in VA. now just a flake or two every now and then

Posted by: stuff123 | February 20, 2008 1:22 PM | Report abuse

Been snowing lightly for about an hour, nothing sticking to the ground yet.

Posted by: Ashburn | February 20, 2008 1:24 PM | Report abuse

Time will tell whether the gap in precip over Northwest Virginia is real or just a mountain-based radar glitch. Light snow in Mclean.

Posted by: mcleaNed | February 20, 2008 1:29 PM | Report abuse

One creature is certainly happy about Friday's potential winter weather - my cat. I postponed his scheduled vet appointment until next week, just in case things are nasty.

Posted by: natsrgreat | February 20, 2008 1:29 PM | Report abuse

Nice little flurry burst on Capitol Hill.

Posted by: Mike from the Blue Ridge | February 20, 2008 1:34 PM | Report abuse

Just got this email: Montgomery County Schools: Evening Activities Cancelled. There is nothing happening in Potomac - a few breezy flakes...

Posted by: marlee | February 20, 2008 1:34 PM | Report abuse

augusta jim or some other weather guy:

i was thinking about how i've seen a few flakes today - probably on the order of 1,000,000 even though it's just flurries, and i got to wondering.....i know it depends on temp/pressure and probably a bunch of other stuff, but how many snowflakes would you say are in an "average" 1 of snow?

Posted by: walter (falls church) | February 20, 2008 1:37 PM | Report abuse

Snow falling in Rockville in the parking lot

Snow falling in Springfield on my telescope


Posted by: Bikerjohn | February 20, 2008 1:39 PM | Report abuse

Overall radar trend looks rather anemic to me. Can even a clipper disappoint?

Posted by: GAD | February 20, 2008 1:43 PM | Report abuse

Walter of F.C. - Lord knows how many snowflakes are in a cu. in of snow. Just think of this though, the "millons" of snoflakes you have seen are acutally "billons" of snowflakes because typically a "snowflake" is an aggregrate of numerous of snowflakes all sticking together. Rarely do you see a single dendrite or column on its own unless it is extremly cold.

mcleaNed: that radar glitch is actually a rain shadow that is being cast by the crest of the Allegheny Front to the west. The winds on the east side are downslopping and that is why the Shennandoah valley is dry right now, and is in fact the driest part of the state because of it.

Posted by: Nader | February 20, 2008 1:46 PM | Report abuse

yes i've noticed how "flakes" are actually clumps of flakes. sometimes, against a black jacket or something, i think i can see actual single flakes (dendrite?) break off a clump of flakes.

anybody else? how many flakes in a

Posted by: walter (falls church) | February 20, 2008 1:56 PM | Report abuse

Snowing moderately in Baltimore, vis. below 1/2 mile downtown (cannot see halfway to Hopkins Hospital from 6th floor of SHA @ JFX & Monument St.)

Posted by: Chris | February 20, 2008 1:59 PM | Report abuse

RE: Earlier question on sun angle
Today: 39° (same as late Oct.)
Dec. 5: 28°
An overrated factor in precip type, IMO, however.

Posted by: Steve, Capital Weather Gang | February 20, 2008 2:06 PM | Report abuse

YAWN ! This snow is boring...I mean these tiny few flakes falling are boring.

Posted by: Jenn in Reston | February 20, 2008 2:13 PM | Report abuse


I can understand your opinion that the sun angle is overrated when it comes to precip type, but isn't there some "value" in the sun angle when it comes to snow/ice sticking to surfaces, particularly the roads? I have no scientific reason behind that, but it seems like a logical conclusion.

Posted by: Ivan | February 20, 2008 2:14 PM | Report abuse

Any predictions on if the sky will be clear enough for eclipse watching tonight? I've had this day circled on my calendar for months.

Posted by: DC Centurion's Shield | February 20, 2008 2:18 PM | Report abuse

The boundary layer, despite the snow aloft, is just too dry. Nothing but off and on very light flurries here in Vienna (2 PM). The models, in this type of situation, like with persistant cold-air damming, aren't very accurate They do a pretty good job of showing the moisture coming in aloft. but fail to take into account that with low dew ponts at the surface, most of it will remain virga for awhile until the lower layers moisten up. Forecaster often fail to recogniize this.....just as they often underestimate the effects of cold air damming that models can't pick up east of the ridges.

Posted by: Mike | February 20, 2008 2:21 PM | Report abuse

Starting to get a dusting on grassy area's here..

Posted by: arnoldkh | February 20, 2008 2:22 PM | Report abuse

For the sun angle range we're talking about, time of day and duration and thickness of cloud cover would be more important factors in heating the ground. For example, the difference between noon values today and Dec. 5 is about the same as between 9:30 this morning and noon.

Posted by: Steve, Capital Weather Gang | February 20, 2008 2:24 PM | Report abuse

Sun angle by time of day is here.

Posted by: Steve, Capital Weather Gang | February 20, 2008 2:32 PM | Report abuse

This is positively underwhelming.

Posted by: Southside FFX | February 20, 2008 2:40 PM | Report abuse

This snow 1" they were calling for around the DC area. Not going to happen (MARK MY WORDS). We call it the Moses effect... the storm just splits and goes North and South of this area. It just does not want to happen above us. Just a few little flakes and that will be it. Oh yeah, wait until Friday. Another let down... more rain if anything! I do want snow but just keeping it REAL!

Posted by: battman | February 20, 2008 2:42 PM | Report abuse


LOL - Just kidding, if there was a funny/sarcastic font the above sentence would definitely be in that.

Not a flake to be seen. My bus driver said it snowed like 5 flakes around 1230 and that was it, so humph.

But, I didn't get my hopes up to high from this clipper. We have been warned time and time again that the mountains steal all their moisture. Blasted mountains!!!!!!!!

At least there is tomorrow night/Friday, right? :)

Posted by: weatherdudeVA | February 20, 2008 2:42 PM | Report abuse

battman: LOL at the Moses effect. I call it the PWC bubble, because everything always seems to wrap around Prince William County

Posted by: weatherdudeVA | February 20, 2008 2:44 PM | Report abuse

Agreeing with the other commenters - unless I am missing something, radar indicates this might be it, right?

Posted by: Southside FFX | February 20, 2008 2:47 PM | Report abuse

I think Old Man Winter hates us.

Posted by: Yellow | February 20, 2008 2:54 PM | Report abuse

Quick Question... Is the late week storm a coastal storm, or is it tracking west of DC?

Posted by: Anonymous | February 20, 2008 2:57 PM | Report abuse

All grassy areas are not whitened here, and we continue to see light/moderate snow. Temperature has been dropping since noon, now sitting at 26F. Areas just north of I-70 in Carrol and Baltimore counties seem to be getting the best of the snow so far.

Posted by: arnoldkh | February 20, 2008 3:00 PM | Report abuse

its not sticking in bethesda

Posted by: d | February 20, 2008 3:01 PM | Report abuse

Unidentified Questioner: I am under the impression that it'll be a coastal storm, but don't quote me on it.

Posted by: weatherdudeVA | February 20, 2008 3:04 PM | Report abuse

any predictions for school friday coming soon? ive heard some optimistic predictions (for students, anyway). how much snow is predicted for thursday night only?

Posted by: h j | February 20, 2008 3:04 PM | Report abuse


1-3 inches

Posted by: d | February 20, 2008 3:12 PM | Report abuse

Finally have a more consistent snow in Rosslyn.

Posted by: Scott | February 20, 2008 3:14 PM | Report abuse

Nothing happening in NW Spotsy. Late week storm looking more interseting but still not expecting a major snow, looks like some snow with a fair amount of sleet & ice. A slight change in the storm track could change everything. Will b interesting 2 see how it works out.

Posted by: VaTechBob. | February 20, 2008 3:14 PM | Report abuse

Heyyy, finally something is happening. Really tiny flakes. It's a steady light snow. The temp has dropped 4 degrees since it started a few minutes ago, down to 32 from 36. Wow.

Posted by: weatherdudeVA | February 20, 2008 3:19 PM | Report abuse

WeatherdudeVA.. looks like a decent batch is heading towards Lake Ridge from the southeast..

Posted by: Z-man | February 20, 2008 3:25 PM | Report abuse

Moderate burst of snow here... really tiny flakes

Posted by: Skywalker, Union Station | February 20, 2008 3:26 PM | Report abuse

I'm in Sykesville (Carroll Co.) and it's been coming down steady since noon. The asphalt is still clear but the grass, etc. is looking pretty. I've got 1.5" on my deck railings. Maybe we're in the "sweet spot", clipper-wise. We were the last time (Dec-07)...enough to plow but no need for the snow thrower. Frankly, I hope to clear the season without using the snow thrower.

It's going to be a nice drive to work tomorrow with the moon high and the snow reflecting the moonlight.

Posted by: malditof1 | February 20, 2008 3:35 PM | Report abuse

The clipper was centered over south central Va. at 3 pm, with greatest pressure falls over ne N. Carolina.

As is often the case with clippers, most of the moisture was lost crossing the mts. These are already moisture starved systems,therefore when moving into already dry air, they don't have much to work with.

Hopefully snowlovers will have more to cheer about on Friday morning, but don't bet the bank on it. The potential for Thursday night and Friday is having a tough time getting it's act together within the "model' world. The 18z NAM is coming in a little more aggresive tomorrow night with timing and qpf but nothing really impressive.

3:30- 34 degrees with light snow, no.acc.

Posted by: Augusta Jim | February 20, 2008 3:36 PM | Report abuse

FYI - New post/update is up on main page! :-)

Posted by: MoSno | February 20, 2008 3:38 PM | Report abuse

The "Moses effect" looks kind of like a scraper on an icy windshield ...

Posted by: greenbelter | February 20, 2008 4:09 PM | Report abuse

Steady snowfall and about 1/4-1/2 inch of accumulation in places
It looks like it might be sticking on the roads soon

Posted by: Kirby | February 20, 2008 4:21 PM | Report abuse

Snowing here in Burke, VA. Accumulating!

Posted by: Yellow | February 20, 2008 4:42 PM | Report abuse

Some of the saddest snowflakes I have seen in my life fell near Old Town Fairfax today on/off from noon to 3:00 - NO accumulation to speak of anywhere. :'o( I'm very curious to see what will happen later this week!

Posted by: LNelle | February 20, 2008 5:14 PM | Report abuse

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