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Posted at 10:30 AM ET, 01/21/2010

Forecast: Unsettled & wintry through Friday

By Josh Larson

* Winter Weather Advisory far N&W burbs tonight & tomorrow (map) *
* Coleman's climate conspiracy theory | Temps & more: Weather Wall *

Today's Daily Digit
A somewhat subjective rating of the day's weather, on a scale of 0 to 10.
4Partly sunny & cool with wintry mess possible tonight.
Get tomorrow's 'Digit' on Twitter tonight

Today: Partly sunny. Slight chance of light sleet or rain late. Near 40. | Tonight: Cloudy. Wintry mix likely. 32-36. | Tomorrow: Morning mix, then mostly cloudy. 37-40. | A Look Ahead | Get Express Forecast by E-mail


The next 36 hours are marked with wintry uncertainty. First, a slim chance this morning of a bit of sleet or wet snow across the southern suburbs; most likely a non-issue. Then, by later today another -- stronger -- system will approach from the south. However, how far north this precipitation will make it and whether it will be cold enough for snow are still questions we're grappling with. At this point we think the best potential is for a light sleet/snow mix overnight through early tomorrow, mixing with rain south and east of the beltway. A slushy 1-2" of sleet and snow accumulation is possible in the normally colder north and west suburbs.

Radar: Latest regional radar shows movement of precipitation over past three hours. Powered by HAMweather. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

Today (Thursday): We'll wake up to mostly cloudy skies across the area with a very slim chance of a few flakes of wet snow across our (far) southern suburbs. The balance of the day will be partly sunny and cool with highs around 40. By late afternoon clouds increase again and some light sleet or rain is possible (30% chance). Confidence: Medium-High

Tonight: We'll have cloudy skies with a 60-70% chance of intermittent sleet and/or snow, possibly mixing with rain south and east. Most of the precipitation will likely begin after rush hour this evening and continue through the early morning hours Friday. Overnight lows will range from the low-to-mid 30s. Confidence: Low-Medium

Keep reading for more information on this winter weather threat, including detailed questions and answers...

Tomorrow (Friday): Overcast skies at wake-up with a 70% chance of a wintry mix in the immediate D.C. metro area, with more snow and sleet north and west of the beltway and more rain south and east of the beltway. The coastal system responsible for this threat of precipitation should push off to the east by mid-day so any precipitation should end around this time. Mostly cloudy skies will linger for the rest of the day, though, with highs in the upper 30s. Confidence: Medium


What type of precipitation do you expect? It appears that temperatures will be at, or a couple degrees above, freezing through most of the duration of the event in the immediate metro area. The dreaded wintry mix appears to be most likely. Meaning, a blend of sleet and snow (sometimes more of one than the other), with rain mixing in at times, especially south and east of town.

Who stands the best chance for accumulating snowfall? Probably locations north and west of the beltway such as Sterling, Germantown, Clarksburg and Leesburg and Warrenton, assuming the precipitation does not cutoff south of these locations. These areas may see 1-2" or so of snow and sleet accumulation. A sloppy inch of sleet and snow is possible (50% probability) inside the beltway, with little accumulation to the south and east.

When will this storm start? Some spotty light mixed precipitation is possible by late afternoon. But we expect that the bulk of the precipitation will enter the region sometime after evening rush to as late 1 or 2am. The precipitation associated with the system will generally be entering the region from southwest to northeast; precipitation start times will vary accordingly.

If this system is mostly snow, will it stick? If some heavier bursts of snow and/or sleet materialize, some light accumulation is possible, even on roads. However, cooler surfaces like grassy areas, car tops, will probably get the bulk of the accumulation etc. In the immediate D.C. metro area we think there is a better chance than not that roads will remain wet (or at worst, slushy) as opposed to icy.

What will conditions be like in the wake of this system? Precipitation should exit the region by mid-day Friday. We'll be left with mostly cloudy skies and chilly highs struggling to reach 40. We'll have partly to mostly cloudy skies Friday night with lows in the upper 20s. On Saturday we're expecting the return of sunshine, but high temperatures will remain on the cool side: in the low 40s. Milder Sunday, but with rain likely with highs near 50.

By Josh Larson  | January 21, 2010; 10:30 AM ET
Categories:  Forecasts  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Update: Chance of accumulating snow dropping
Next: "Bench" marking Washington's historic snows


As luck would have it, I have several appointments after work taking me from Arlington, to Falls Church, to Annadale, to Alexandria. All from 5:30PM onward. I am hoping the roads are warm enough and that any nasty stuff will not have had long enough time to cause major issues. That would make for an even worse rush hour. I would love to cancel at least one appointment, but not sure if that is silly, given the circumstances. Not sure I have reason enough-if precip. starts early evening, roads should be ok for a bit. Right?

Posted by: Snowlover2 | January 21, 2010 6:07 AM | Report abuse

aaaww man....!

ggrr... all the lollipops, fangs and cotton balls are gone... just macaroni... booo... booo.... (nonetheless i appreciate the honesty...) darn!

Posted by: walter-in-fallschurch | January 21, 2010 7:20 AM | Report abuse

From the looks of things right now, the Sunday storm may have a greater impact region-wide than the little bit of icing we may or may not get tonight and tomorrow. There's some potential for flooding, particularly in the mountains with the Sunday storm. Lots of rain and warm temps.

Posted by: ThinkSpring | January 21, 2010 7:27 AM | Report abuse

thanks for "Probably locations north and west of the beltway such as Sterling, Germantown, Clarksburg and Leesburg and Warrenton, assuming the precipitation does not cutoff south of these locations."

the "beltway" designation is appreciated. also, naming towns is great for specificity too. thanks again.

Posted by: walter-in-fallschurch | January 21, 2010 8:05 AM | Report abuse

Anyone else bummed at this more stormy pattern? get out and enjoy the sunshine through early afternoon today!

Posted by: Camden-CapitalWeatherGang | January 21, 2010 11:46 AM | Report abuse

Camden - Include me on that list. Love the sun today though! Gonna go for a long lunch walk. Temps have risen nicely this morning.

Posted by: ThinkSpring | January 21, 2010 12:06 PM | Report abuse

Yep, ThinkSpring...too darned much rain/warm-air advection Sunday...still in the dead of meteorological winter!

Sunday's storm would be far more appropriate for mid- to late-March. Let's get back to the cold stuff for a change. I could still give winter a "B-minus" grade if Presidents' Day Week "busts" with more WAA. If we don't get some CAA next month, and we stick with this BORING El Nino warmth, Winter 2009/10 could still earn a "C" or lower. Nearly all the December snow is gone around here.

Josh, no SLCB today, even for North and West???

Posted by: Bombo47jea | January 21, 2010 2:23 PM | Report abuse

Okay, CWG, teach me.

Looking at the national radar loop, it appears that the coastal and upper level low are splitting. Is the coastal storm supposed to head north when it hits the coast? Are we gonna get brushed by it as it goes out to sea? Or are we gonna get something from the upper level system in the Midwest?

Just trying to learn a little something here. Thanks!

Posted by: ThinkSpring | January 21, 2010 2:33 PM | Report abuse

Bombo47jea, no SLCB because they generally refer to the immediate DC metro area, where I anticipate most, if not all, of the storm will be rain -- at worst, non-sticking wet snow/sleet. As for northwest suburbs, they still have some potential for a couple inches. Personally, I strongly believe the best chance for (accumulating) snow will be southwest of DC -- in central VA, places like Front Royal and Harrisburg. If I were forecasting just for that region I'd definitely have a SLCB up...

Posted by: Josh-CapitalWeatherGang | January 21, 2010 2:53 PM | Report abuse

camden, you said,
"Anyone else bummed at this more stormy pattern?"

uh...if by stormy you mean rainy, YES! any chance you mean snow stormy...?

Posted by: walter-in-fallschurch | January 21, 2010 2:56 PM | Report abuse

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