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Posted at 2:30 PM ET, 01/18/2011

Snow/mix chance returns Thurs. night & Fri.

By Jason Samenow

With the ice storm in our wake, it's time to look forward to the next chance of accumulating snow which arrives Thursday night and may continue into part of Friday.

Next accumulating snow chance: Thursday night & Friday morning
Probability of accumulating snow (1" or more): 30%
Probability of more than 4": 10%

This doesn't look to be a huge storm as it will be a fast mover. But for at least parts of the region, the storm may be strong enough to produce light to moderate amounts of precipitation, which may fall in multiple forms rather than being all snow. Wes Junker, our winter weather expert, says: "There are potential mixing and precipitation type issues especially from the city eastward. If the storm were all snow it looks more like a dusting to 3 inch event than one that would produce over 3 inches."

The set up for this storm is pretty complex. A fairly energetic upper level disturbance will approach from the west, with low pressure at the surface potentially tracking through the region. Exactly where the surface low tracks will help determine how much cold air is in place as the storm arrives. A track more to the south would help ensure snow for most of the region, whereas a track further to the north would favor more of a mixed precipitation scenario.

As the low nears the coast, it will redevelop into a coastal storm and intensify. Exactly where and how fast the low redevelops will determine where the heaviest precipitation occurs. As with past storms this year, it may be locations north and northeast of the District that get the most snow.

Enough cold air should be in place at the surface and aloft for the precipitation to fall as snow north and northwest of D.C - that's assuming the low tracks over the region or to the south (a track more to the north could cause mixing issues even in the colder parts of the region). But as you head south and east, mixed precipitation is a possibility - particularly during the first phase of the storm (and if the low tracks too far to the north, there could even be rain). Unlike Monday night's storm, cold air will be coming in rather than moving out.

This an admittedly brief overview of this storm. But Wes Junker will provide a full analysis breaking down the models in a post tomorrow.

By Jason Samenow  | January 18, 2011; 2:30 PM ET
Categories:  Latest, Snow Lover's Crystal Ball, Winter Storms  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Reviewing a slippery forecast & photos
Next: PM Update: Some rain tonight, mix northwest


Only a 30% chance of 1"??? I'm throwing in the towel.

Posted by: BobMiller2 | January 18, 2011 2:37 PM | Report abuse


We may be a little bit too south to cash in from this one...but it's close. I actually think this map from Henry Margusity (who sometimes overforecasts snow for us) seems like a reasonable first guess (he has us in the coating to 3" category):

Posted by: Jason-CapitalWeatherGang | January 18, 2011 2:56 PM | Report abuse

Ummm.....yay for snow?
Boo for any other sort of precip. We received quite the variety pack last night & that's enough. &#*%@*!& typical DC winter weather....troublesome to predict & hateful to deal with.

Posted by: FIREDRAGON47 | January 18, 2011 2:58 PM | Report abuse

That's odd. 12Z runs of the GFS, JMA, and Canadian all have about .5 total precip in the DC/MD area for Friday with the freezing line along or south/east of I95. 12Z NAM is rolling in now. The accuweather guys (Margusity and Bastardi) are saying 3-6 inches for our area on Friday and Berk is saying Friday's snow "should more that double Baltimore's seasonal snow total". All three have done well with the last several storms. Just curious what you guys are basing the dusting to an inch on?

Posted by: DLO1975 | January 18, 2011 2:59 PM | Report abuse

ennepe68 and i like that 10%

Posted by: walter-in-fallschurch | January 18, 2011 3:00 PM | Report abuse

@Jason-CapitalWeatherGang You are right. Margusity's map is just north of DC with the 3-6 line; but he does talk about 4 inches for the Mid Atlantic area as a general expectation in his blog post. Bastardi (in his video post) has DC in 3-6 as well, but expects some higher totals north and west of the city. I'm sure the models will do their usual back and forth the next few days.

Posted by: DLO1975 | January 18, 2011 3:03 PM | Report abuse


We're not forecasting a dusting to an inch...but erring on the side of being conservative 84 hours out with probabilities - especially since, as modeled, the position of the upper low and surface low are not ideal... not to mention the seasonal trend. Plenty of time to bump the probabilities up if warranted.

Posted by: Jason-CapitalWeatherGang | January 18, 2011 3:06 PM | Report abuse

I'm a-ok with completely missing an ice storm, thanks.

Posted by: oldtimehockey | January 18, 2011 3:09 PM | Report abuse

oldtimehockey - would you say you are a snow lover at all, though? Or perhaps just not a fan of winter overall. Though, yes, the dangers and serious impacts of an ice storm are pretty much undesirable--across the board.

Posted by: Camden-CapitalWeatherGang | January 18, 2011 3:12 PM | Report abuse

@Jason-CapitalWeatherGang Understood. Was just curious if I was interpreting the model outputs incorrectly, as they do see to at least be giving us a chance of something more significant at this point. You guys certainly understand the models a lot better than most of us do! As for Bastardi and Berk; they are more agressive up front in calling things early. Sometimes it pays off and sometimes it doesn't.

Posted by: DLO1975 | January 18, 2011 3:14 PM | Report abuse

Lets root for that 10%!

Posted by: cubscapsfan | January 18, 2011 3:14 PM | Report abuse

The sun is starting to come out here in NE Loudoun. So far today, the high temp on my deck has been 32.6°F, but maybe it'll go up a bit more.

Posted by: BobMiller2 | January 18, 2011 3:17 PM | Report abuse

According to Henry Margusity's map, my residence (middle of Montgomery Co., right by I-270) sits almost exactly on the line between coating to 3" and 3-6", so I guess I can call it at 3. Same for Baltimore City. (I'd guess the projected total goes down the closer we get to any actual weather, though.)

Accuweather, for what it's worth, sees a continuing pattern of storminess through at least early February. And this quote will please some people on here (and worry others): "Even some of the "snow holes" in portions of Pennsylvania, Maryland and the Virginias will likely be filled in with this pattern."

Posted by: mkarns | January 18, 2011 3:25 PM | Report abuse

@Camden, I like ice fine: on the rinks or the ponds, but not on roads/trees. Snow I can deal with. I tried almost successfully to use my road as a curling venue this morning. No thanks.

Posted by: oldtimehockey | January 18, 2011 3:30 PM | Report abuse

I am wondering, CWG, what is the likelihood of a refreeze on the roadways tonight, and what time that would happen? I have to pick up my daughter around 8 pm in a spot that is notoriously bad for icy road conditions, and I am wondering if I should plan an alternate route.

Posted by: squirrelgirl1 | January 18, 2011 3:33 PM | Report abuse

mkarns - I just want to temper expectations when we are still so far (80+ hours) away from the next possible winter storm system.. that predicting accumulation numbers are low confidence still. Don't fixate, at least yet, on the 3" number. We will keep you updated as information becomes more reliable. Sometimes forecasters can be irresponsible when projection numbers too far in advance, and it troubles me. It just isn't something that can be mathematically justified to say with confidence this far out. Jason & Wes are good to keep such a range at this point-- reasonable expectations for a "dusting to 3 inches" with a 10% chance of more than 4 inches. Hope this makes sense. Capital Weather Gang doesn't want to ever be unreasonably deterministic in our forecasting, until we can deliver information with better confidence closer to winter storm events!

Posted by: Camden-CapitalWeatherGang | January 18, 2011 3:33 PM | Report abuse

I keep getting my hopes up...these little bitty storms are NOT good for a snow lover!! I just want one big one....I am beginning to think that is going to be to much to ask for this winter :(

Posted by: Hopin4Snow | January 18, 2011 3:34 PM | Report abuse

There are reasons to stay conservative on the Thursday night into Friday event. The SREF ensemble members which suggested today's storm had more potential to reamin all cie than we gave credit to east of DC have lots of mmebers saying upcoming event may have ptype issues. You can look at a plume diagram and see all the sref member precipitation at this site Set it for the 15Z run and DC and you'll get the product. The mean precipitation from all the sref runs is .25. The mean snowfall is 0.08 so there are more rain members than snow members

Posted by: wjunker | January 18, 2011 3:37 PM | Report abuse

oldtimehockey - curling? wow. But it certainly is not "fun" to have ice anywhere but ponds or rinks--agreed.

squirrelgirl1 - play it safe, even though I don't believe in a large-scale refreezing tonight would occur, this cold air could easily pool in a low-point in roads tonight and be instantly treacherous.

New update coming momentarily from Jason - check back on homepage for tonight's latest forecast wherein Jason will address re-freeze questions

Posted by: Camden-CapitalWeatherGang | January 18, 2011 3:39 PM | Report abuse

What I think is really amazing about Henry's map is that--in a departure from his recent maps--the colors on the map match the legend.

Posted by: spgass1 | January 18, 2011 3:40 PM | Report abuse

Interesting new product from HPC over at the NWS. Still listed as experimental but I think it's been viewable for almost a year.

Been tracking its performance over the last few potential snow events for DC. Has consistently overdone the percentages by about 20%. Currently shows DC metro with a 60% of 1 inch or more, so probably more like a 40% chance. Very close to CWG's probability currently forecasted.

Posted by: HurricaneSpud | January 18, 2011 3:40 PM | Report abuse

If it's 36 degrees, why isn't this stuff melting? I'm near Baileys Crossroads - can't be that much colder than National Airport!

Posted by: dottie_b | January 18, 2011 3:42 PM | Report abuse

I was wondering if anyone could help me out. I was looking at the 12z run of the GFS and could easily see the position of the surface low at hour 66 (NC/ VA border) and hour 72 (at the mouth of the Delaware River). Jason, you had a mentioned an Energetic upper level disturbance. Which maps do I have to look at to see the exact location of the upper level disturbance during those hours and what should I be looking for on the map? Also.. Earlier runs of the GFS (I think it was sunday) had this system tapping in to gulf moisture. But based on the the 6 hour precip outputs, it looks as though the moisture feed from the gulf dries up. What type of features should I be looking for to indicate a moisture flow from the gulf?

Posted by: jac8949 | January 18, 2011 3:47 PM | Report abuse

wake me up when spring is here

Posted by: KRUZ | January 18, 2011 3:56 PM | Report abuse


Look at the 500 mb (approx 18000 feet) map of upper level heights (pressure), wind, and vorticity. Where you see the dip (trough) in the upper level winds and pressure lines and attendant curvature in the flow, that's where you get disturbances with spin in the atmosphere -- aka vorticity. Vorticity promotes upward vertical motion and precipitation. Where you see the brightest shades of orange and yellow are where the vorticity maxima are. We call these vort maxes. Sometimes they're marked with X's on the map. those are the disturbances.

Posted by: Jason-CapitalWeatherGang | January 18, 2011 4:01 PM | Report abuse


One more thing: In this situation, there are two vorts involved. The main vort (most energetic) is the one over the Ohio Valley. There is another weaker vort to the south (along the southern branch of the jet stream) which has a little, but not much Gulf moisture associated with it at the surface. It's kind of losing energy -but models do eventually have it combining or phasing with the disturbance over the Ohio Valley when it reaches the coast. That's when the coastal storm forms.

Posted by: Jason-CapitalWeatherGang | January 18, 2011 4:07 PM | Report abuse

Here's my feelings CWG. It looks like you could draw a / line from dc to baltimore...anyone south of the line will have manly rain durning this next event and a very slight chance of any re-frezze. Anyone in North/West of DC like you guys said will get rain/freezing rain. CWG I disagree I think that anyone in Thurmont, Emmitsburg, New Market, Mount Airty, Damascus, Gaithersburg (AKA anyone from Northern Montgomery and up anywhere from North to west of these locations) will see a nice re-frezze (as in damascus we have not been above 32 all day maybe 32.5) and will prob. see frezzing rain/snow durning this event. My question (you guys are doing a great job and I am far from knowing what you guys know) could you tell me how much snow is possible (if it was to be all snow) how much ice is possible (if it was all ice) and how much rain is possible (if it was all rain) no one has ansawer this. Do we know?!?! Will the system have trouble getting over the mounts. and weaken. As of right now it looks like a promblem for anyone North/west of DC

-thanks dan

Posted by: danrusso10 | January 18, 2011 4:14 PM | Report abuse

Hey dan... I am new to this but I think the key difference with this Friday's storm is that it will be "ushering in" cold air so that once the storm has moved over us the vertical profile of temperatures should support snow. With this morning's storm there was a lot of warm air advection and the Easterly flow aloft caused warmer temperatures aloft. I could be wrong, but I dont think that we will have the same set up on Friday. So it should be a mix to snow event, instead of a snow to mix event.

Posted by: jac8949 | January 18, 2011 4:38 PM | Report abuse


I was actually talking about the rain/ice storm tonight (**ITS SUPPOST TO BE MINOR) but I was saying that if Northern Montgomery, frderick ect got a re-frezze and another 1/10 of an inch of ice we would have another mess. It is currently 32.3 in damascus, so my point to CWG and other weather forcasters (I know they look at the main event now a couple of countys) but how is this going to be rain if its at or below frezzing in these locations north/west of DC

-thanks my bad for the mis-understanding

Posted by: danrusso10 | January 18, 2011 4:50 PM | Report abuse

Thx Jason. I found the Vort Max and dips you were referring to. that helps a lot.

Posted by: jac8949 | January 18, 2011 4:51 PM | Report abuse

@Camden, ok, I was kind of kidding about the curling. But our street was completley covered and untreated with bumpy ice (curling ice is slightly pebbled, for those who don't know). We tried to push a few large rocks down the street and it kind of worked.

Posted by: oldtimehockey | January 18, 2011 4:53 PM | Report abuse

Possible *6 inches* for us Thursday night/ Friday morning. That's what AccuWeather says. How accurate is that??? Hoping we do get that much!!!

I'm *praying for more than 4 inches* this time...

Posted by: SNOWLUVER | January 18, 2011 5:34 PM | Report abuse

There has been a tendency for both man and models to overforecast snow this year.

Tonight's event is a minor, nothing worth mentioning.

The Thursday night event looks like an inch or so unless the trough sharpens up more than forecast. When the vort max goes north of you, it is rare to get heavy snow.

There could be something more significant next week, but it will depend on complex interaction among multiple systems and it's way too early to venture any real guess.

Posted by: frontieradjust | January 18, 2011 7:32 PM | Report abuse


Completely agree!

Posted by: Jason-CapitalWeatherGang | January 18, 2011 8:46 PM | Report abuse

The Accuweather app on my iPhone shows 1.2 inches of snow predicted for Thursday evening/Friday morning. I regularly see people post here with different Accuweather predictions than my app shows. I can see why there would be variations if we were checking days apart, but that doesn't seem to be the case. Has anyone else noticed this?

Posted by: kg2273 | January 18, 2011 9:40 PM | Report abuse

so the gfs and nam show this storm for us thursday/friday but what about the euro?... the weather channel on tv, internet and app show nothing for thurs/fri. they didnt even mention it for us in the broadcast. she just showed everything being to our north.

does the weather channel hug the euro model?... or is the euro in line with the gfs and nam?

the latest gfs seems to have us pretty close to some of that darker green....

Posted by: KRUZ | January 18, 2011 11:29 PM | Report abuse

yep confirmed again, just watched the weather channel show thurs/fri storm and he showwd 2 tracks. 1 far south and way ots the other far south and ots enough to pass us by and hit ny and further north. he literally said both scenarios leave dc in the cold and showed just clouds for us. he said they are siding with scenario 1 which is the far south and ots solution. this is no where near what the gfs and nam are showing what models are they looking at to get these 2 scenarios that are total misses cor us thurs/fri?... im just curious what models twc uses.

Posted by: KRUZ | January 19, 2011 12:15 AM | Report abuse

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