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Posted at 7:45 AM ET, 12/17/2009

Weekend snow prospects increase

By Josh Larson

Some chance of significant accumulation

* Cold continues, snow threatens: Full Forecast & Daily Digit (new!) *
* NOAA's snow probability maps (see day 3) *

Next Chance of Accumulating Snow: Saturday - Sunday
Probability of Accumulating Snow (1" or more): 65%
Most Likely Potential Impact:

The potential weekend snow threat that we've hinted at for the past several days is becoming more likely. An area of low pressure will develop over the Gulf of Mexico today and that storm system will generally take a northeasterly track to somewhere off the Southeast coast by Friday.

The question, as with any potential coastal storm affecting our region, is exactly what track this system will take. Namely: will it take a more southerly/easterly track and just graze us (or even miss us altogether), or will it "turn" up the coast, socking us with snow? This is still unclear, though models over the past 24 hours have seemed to suggest the latter is increasingly likely.


Regardless of the actual track of this storm, and somewhat rare for the metro region, it appears that there likely will be enough cold air in place to assure that most, if not all, precipitation that falls should be in the form of snow. (There is just an outside possibility that the storm would track far enough inland to introduce a chance of a wintry mix along and east of I-95, as opposed to mostly snow)

Note that areas south and east of metro D.C., at this point in time, have a better chance at seeing snow than areas further north and west. The storm will not be fast moving so there is potential this could be a long-duration event for some areas -- beginning late Friday night and lasting into early Sunday.

As always, keep checking back for updates.

The Snow Lover's Crystal Ball appears when the potential exists for accumulating snow beyond 24 to 36 hours.

By Josh Larson  | December 17, 2009; 7:45 AM ET
Categories:  Snow Lover's Crystal Ball  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Forecast: Cold is here, weekend snow threatens
Next: A look back at last week's historic weather


Dang! accuweather predicts 8.7 inches for bethesda

Posted by: samdman95 | December 17, 2009 5:37 AM | Report abuse

Weekend snow - love it.

Cold enough to snow - love it.

Increasing chances of snow - love it.

Talking about it at CWG - love it.

Uncertainty of track - hate it!

Posted by: jaybird926 | December 17, 2009 5:50 AM | Report abuse

So Accuweather was right after all?

Personally, I'm hoping for a light accumulation.

Posted by: Murre | December 17, 2009 6:18 AM | Report abuse

personally im hoping for a foot! is that possible if the storm travels closer to the coast than expected?

Posted by: samdman95 | December 17, 2009 6:21 AM | Report abuse


I think there's about a 10% chance of 1 foot or more. The scenario for that would be for the storm to take a slightly more westerly track (closer to the coast) than currently simulated.

Posted by: Jason-CapitalWeatherGang | December 17, 2009 7:44 AM | Report abuse

The chart above shows 35%, or best chance, for Sat. for 1" or less. So where are all these high numbers coming from?

Reasking - Hosting a kids' bday party Sat. pm Gaithersburg. Thoughts?

Posted by: Post43 | December 17, 2009 7:53 AM | Report abuse

So, the biggest Christmas shopping weekend for retailers will be ruined.

Just what the local economy needs.....Not.

Hoping for only a glancing blow here.

Posted by: ThinkSpring | December 17, 2009 7:59 AM | Report abuse

There's a Carly Simon song going through my head right now..."Anticipationnnnnnn, anticipayaytion..."

Posted by: mcaicedo | December 17, 2009 7:59 AM | Report abuse


If the storm takes more of an easterly track, we may just be talking about light snow or less, meaning a Saturday afternoon birthday party could still work. At the moment there looks to be about 1 in 3 chance of that. But there is a lot of support in computer model simulations and the overall pattern for something more than that. We'll have greater confidence in the ultimate scenario this afternoon and especially by later tonight and tomorrow.

Posted by: Jason-CapitalWeatherGang | December 17, 2009 8:11 AM | Report abuse

Love the forecast! I hate how you keep using the phrase "snow THREAT," though - for snow lovers like me, it's not a threat; it's a promise. :-)

Posted by: paperball | December 17, 2009 8:17 AM | Report abuse

BabyARC's 2nd birthday party is Saturday - so thats two of us in the Party or Not to Party boat (actually, its cancel or continue with the On the Border catering; personally I say bring the chimichangas on - Ill eat them!) Well, I did promise her snow for her birthday! I have a pretty good hunch that we will be seeing both the 4-8 and 6-10 inch number thrown out there with a localized foot...AND - look at that Christmas Eve and Christmas Day setup...we may not need Saturday for a white Christmas.

Posted by: DullesARC | December 17, 2009 8:17 AM | Report abuse

It's funny. You guys are saying "south and east more" everyone down here [RIC] is saying that "north and west" will get more!

Posted by: Registration1982 | December 17, 2009 8:33 AM | Report abuse

Listening to the radio on the way in to work, NPR was talking Friday into Saturday and WTOP was placing the storm Saturday into Sunday. Have events planned Saturday and Sunday mornings. Which one is most likely to get canceled?

Posted by: nonfrequentflyer | December 17, 2009 8:55 AM | Report abuse

Looking forward to tracking the latest model runs this afternoon.

@jaybird926: I couldn't have said it any better. ;)

Posted by: SkywalkerSS | December 17, 2009 9:01 AM | Report abuse

It is interesting that some models seem to be saying south/east, yet Accuweather is predicting a lot of snow for the Shenandoah Valley... "As snow continues into Saturday, totals will likely exceed a foot farther north along the I-81 corridor in northern Virginia."

To prepare for the snow storm, I'm going to buy a yard stick on Friday just in case totals exceed 12". I guess an alternative would be to clear a snow board and add totals. That may actually be better to minimize compaction impacts.

Posted by: spgass1 | December 17, 2009 9:04 AM | Report abuse

ThinkSpring, So that conversation would go something like, "Sorry, I was going to buy you a Christmas present, but it snowed last Saturday. Let's hope for better weather next year."

Posted by: GD1975 | December 17, 2009 9:08 AM | Report abuse

Jim in NOVA here -

I am excited about this storm beyond belief! That said, I have a Christmas / Apt Warming party scheduled for Saturday night from 7pm to midnight roughly.

Right now it's looking like that period may well be the height of the storm. My thinking is I will not "call it" just yet, but it is looking like I may need to do that.

If that's the case, I'm thinking a Sunday daytime event may be better than a Saturday day time event. Any thoughts?

Posted by: jahutch | December 17, 2009 9:12 AM | Report abuse

Thanks, Jason.

DullesARC, when will you decide to call your party? My post party caterer is Grandma, and since she doesn't have 4 wheel drive, no post party food for us :-)

Posted by: Post43 | December 17, 2009 9:28 AM | Report abuse

To everyone having parties this weekend and looking for forecasts:

The invitations to your favorite online weather people must have gotten lost in the mail. That's the only explanation for us just finding out about this now...

But in reality, there is still a TON of info in doubt, including time, intensity, and amount. Right now, the only thing certain is there is a "snow threat that will impact the area between early Saturday morning through late afternoon on Sunday. Snow will likely be present within the metro area." Everything else, while reasonably expected, is still under 50% certainty for and not firm enough to report.

Posted by: JJones-CapitalWeatherGang | December 17, 2009 9:29 AM | Report abuse

Come on Guys, you have to admit the 12z NAM is awe-inspiring. If we got HALF the amount of snow it predicts we'd still be buried.

Posted by: worldtraveler | December 17, 2009 9:33 AM | Report abuse

LOL - JJones, if we do have the party as scheduled, you and the rest of the CWG are welcome to join us!!

Posted by: Post43 | December 17, 2009 9:40 AM | Report abuse

W00T! Snow. Bring it!!!

Posted by: Alexandria2009 | December 17, 2009 9:49 AM | Report abuse

This is a pretty specific question, I won't mind if you don't answer :-) My mom is scheduled to fly out of BWI on Sunday, she lives in Richmond. She had planned to come up here on Saturday, hang out, spend the night and then fly out Sunday. Her flight is later in the day Sunday, is her best bet to stay put in Richmond and just drive up Sunday?

Posted by: ana_b | December 17, 2009 9:56 AM | Report abuse

I'm not sure I agree on 10% odds of a foot or more (somewhere). This has the makings of a historic event wherever the heaviest falls.

Posted by: Ian-CapitalWeatherGang | December 17, 2009 9:58 AM | Report abuse

I want the official prediction to be "dusting to 1 ft.+"

Please hold off until I finish my Christmas shopping.

Posted by: epjd | December 17, 2009 9:58 AM | Report abuse

Silly me - I posted this one on the wrong blog entry...

Anyone else getting suspicious this might be a much bigger deal than we were thinking even 24 hours ago? Like I said yesterday, you'd have to be crazy to see these maps and not be suspicious of a potential big event. I could easily see this thing riding up the coast to be honest. That low parked over Nova Scotia reminds me of the weather map of March 12, 2003. Only two jets phasing, not three, I get that part, but the low pressure and the gradient between it and the high pressure looks very similar. Perfect set-up for cold air bleeding and cyclogensis.

Not a forecast, just a thought. Or perhaps mere wishcasting; we'll see.

Posted by: curtmccormick | December 17, 2009 10:00 AM | Report abuse

Curt, that potential definitely exists. And I have a good feeling about this one...

Posted by: Josh-CapitalWeatherGang | December 17, 2009 10:03 AM | Report abuse

Bring it on! I'm walking distance between both the grocery store and a mall. And I like walking in the snow... :)

Posted by: MKoehl | December 17, 2009 10:07 AM | Report abuse

CWG, are you guys on Facebook?

Posted by: MKoehl | December 17, 2009 10:08 AM | Report abuse

OMG! i just heard about this. wow...chances for snow AND cerrato's "resigning" on the same day!

the big question here is what can i do personally to make sure we get "socked" with snow?

Posted by: walter-in-fallschurch | December 17, 2009 10:10 AM | Report abuse


The 12z NAM would be historic if it verifies (literally it's 18"+). But still too soon to take it to the bank -- that model can struggle beyond 48 hours and it has a wet bias. Need to see the GFS with a similar solution, and consistency at 18z and 0z...then it would be time to honk, loudly.

Posted by: CapitalWeatherGang | December 17, 2009 10:13 AM | Report abuse

Argh, really not trying to do so many posts. But I have to ask - curtmccormick, do you mean March 12, 1993, as in the Blizzard of 1993?

Posted by: MKoehl | December 17, 2009 10:14 AM | Report abuse

@CapitalWeatherGang can you boys post some graphics from the 12z NAM?

Posted by: Registration1982 | December 17, 2009 10:16 AM | Report abuse

CWG, you said,
"historic"! omg... i'm trying not to get too excited, but....

Posted by: walter-in-fallschurch | December 17, 2009 10:17 AM | Report abuse

Registration1982, here's the 60 hour forecast accumulated precipitation ending Sunday evening: It would be correct to assume a snow-liquid ratio of something like 10:1

Posted by: Josh-CapitalWeatherGang | December 17, 2009 10:20 AM | Report abuse

Despite my screen name, I actually hate snow and cold. I know that puts me in a minority here...

Fascinating to read this blog and then check the various news outlets. Makes me wish the news outlets would state their methodology when giving the forecast. WAMU says more or less what you say. WTOP says slight chance of snow. is now with you. WaPo this morning just said cloudy. (I guess you don't talk to the print folks.)

Posted by: oldtimehockey | December 17, 2009 10:21 AM | Report abuse

Not looking too promising for a Saturday afternoon/evening run down to Charlottesville for a UVa basketball game, is it?

Posted by: jburksva | December 17, 2009 10:22 AM | Report abuse

Not really a math chic, but tried figuring out the 10:1 looking at the link. Looks like parts of area could get 3-4" of liquid precip, yes? So, that would mean 30"-40" of snow? I must be doing something wrong.

Posted by: nonfrequentflyer | December 17, 2009 10:24 AM | Report abuse

Even if you cut the NAM in half it's a major snowstorm. There is a lot of agreement at this point outside the NAM. Someone, maybe not us, will probably get over 1' from this storm in my opinion.

Posted by: Ian-CapitalWeatherGang | December 17, 2009 10:29 AM | Report abuse

@CapitalWeatherGang thanks, Josh. If you could inform my curiosity, I'd appreciate it. Why does the NAM come in so much sooner than the GFS?

Posted by: Registration1982 | December 17, 2009 10:31 AM | Report abuse

I'm scheduled to fly from Dulles to San Diego on Saturday afternoon - need to be there for an event Sunday. Debating whether to change to a flight leaving tomorrow morning...much less convenient, but also seems much less likely to be canceled. I may wait to pull the trigger until this afternoon's updated forecast - seems like there will be a slightly better sense of things then?

Posted by: hlg22 | December 17, 2009 10:39 AM | Report abuse

Not talking about snow accumulation for a second, but the one thing that seems to always happen after storms here in DC (especially these sort of costals)? Temps afterwards ALWAYS go lower than projected. With highs already projected to only reach the upper 30's, early next week could be downright frigid around these parts, whether we get 1" of snow or 1'.

Posted by: JJones-CapitalWeatherGang | December 17, 2009 10:39 AM | Report abuse

If we're talking wine, I have a wet bias too. Despite the possibility of some holiday plans being cancelled, I am still beside myself. It's all I can do to refrain from looking at this site the few chances I have in the day. Seriously. I need a snow anticipation suppressor.

Posted by: Snowlover2 | December 17, 2009 10:40 AM | Report abuse

Some of these models made my jaw drop this morning. It will be interesting to look back after this storm and figure out which one made the best call.

Posted by: Tom8 | December 17, 2009 10:40 AM | Report abuse

When can we expect an updated forecast?

Posted by: edwardappleby | December 17, 2009 10:42 AM | Report abuse


The NAM comes in sooner than the GFS because of how it is scheduled on the machine. Since it is a regional model, it relies much more heavily on more conventional data (i.e. weather balloons, etc.), and not so much on remotely sensed data (which takes longer to transmit, receive, process). The GFS (which is a global model) uses a later data cut-off (i.e. it simply waits longer for more data to arrive to initialize).

Posted by: dtkwx | December 17, 2009 10:44 AM | Report abuse

@dtkwx thanks. Much appreciated!

Posted by: Registration1982 | December 17, 2009 10:45 AM | Report abuse

i see what you mean about 18"... on that awesome NAM graphic you linked to we appear to be at 1.75-2". how close to us is that "red dot" (3-4" liquid)? now it appears to me to be about 50-75mi SSE of wash? if that moved over my house, would that really mean 30-40" of snow?!?!

Posted by: walter-in-fallschurch | December 17, 2009 10:47 AM | Report abuse

GFS coming in much lower on precipitation totals but otherwise it looks decent still. Not sure I buy it's solution.

Posted by: Ian-CapitalWeatherGang | December 17, 2009 10:51 AM | Report abuse

Love snow, but having said that, I planned a family trip to sunny Florida . . . leaving from IAD on Sunday afternoon. Always works out that way, doesn't it?

--Jamie Y (aka Weather Checker)

Posted by: JamieYPotomac | December 17, 2009 10:59 AM | Report abuse

@Ian-CWG - GFS is still showing 60 precip totals at 8-12" for much of the area. So although it is lower than 20-30" (which probably isn't going to happen,) it is still decent!

Posted by: snowlover | December 17, 2009 11:03 AM | Report abuse

sorry supposed to say 60hr loop pricip totals

Posted by: snowlover | December 17, 2009 11:03 AM | Report abuse

@MKoehl: yep that's the one. I'm saying the map of 3/12/03 looked similar to this. The big difference is that in the Superstorm, all three jets phased and they were abnormally strong. That was once in a lifetime. This is a two-jet phase. But the "look," a low over Nova Scotia and the high to the West of it will ensure a fresh supply of cold air, and the negative NAO should encourage the storm to run up the coast. This all indicates big storm POTENTIAL. I'm by no means saying Superstorm at all, just that I noticed a strong similarity in the weather maps. Now the models seem to be getting with program. So I continue to feel really bullish about this storm as an overacheiver.

Posted by: curtmccormick | December 17, 2009 11:07 AM | Report abuse

Is Herndon/Reston area looking like the spot to NOT be for this storm? I feel like we might be to far west to get these huge totals that some in the area will see.

Posted by: justin1013471 | December 17, 2009 11:08 AM | Report abuse

snowlover - I agree that the NAM QPF is probably too high, but the GFS is probably too low. The NAM is the model that got the storm two weeks ago right; the GFS has not been very good this season (at least so far).

Posted by: worldtraveler | December 17, 2009 11:08 AM | Report abuse

With high ratios that could be true. I'm not terribly concerned with the precip outputs -- NAM probably too high, GFS may be too low. Other midday models (UKMET/GGEM) also decent hit, so we're still seeing that sort of agreement.

Posted by: Ian-CapitalWeatherGang | December 17, 2009 11:09 AM | Report abuse

@ Post43

We'll wait until tomorrow to revise our party setup - if we are getting 2-4 inches, we will probably keep it going...6-12 or more then, well, not much happens in DC with that kind of weather. It is what it is...that said, bring it on! One thing to remember - the Dec 5 system was captured 10 times better by the NAM than the GFS...just sayin'...

Posted by: DullesARC | December 17, 2009 11:22 AM | Report abuse

I think what many people need to realize is that this won't be a 6 to 10 hour event like 12/5 was. This event per some models could be a 24 to 30 hour event for some parts of the area.

Posted by: jpl1019 | December 17, 2009 11:23 AM | Report abuse

Yes, a long-term event indeed...hasnt been one quite like this since Feb. 03. That storm had quite a bit of early over-running precip associated with it before the coastal took over...this seems to be a strong coastal that doesnt want to move much.

Posted by: DullesARC | December 17, 2009 11:36 AM | Report abuse

Arg! I'm an extreme snow lover myself, but add me to the growing list of folks anxiously wringing my hands over this one due to a a 5 year old's birthday party planned for Saturday afternoon, lots of guests and wasn't cheap...

I'm hoping for a bust on this one.

Posted by: GenerationYforChange | December 17, 2009 11:50 AM | Report abuse

Some of the parties I have enjoyed the most this time of year involved close friends/family being stranded in the snow at someone's house. As long as there is plenty of food and drink and the power stays on it can be fun =)

Posted by: Alexandria2009 | December 17, 2009 11:55 AM | Report abuse

The cold air is in place...plenty of it.

Now the question involves deciding tomorrow evening between going to Gottaswing's Chevy Chase Ballroom holiday dance party, and staying home to watch that FCS championship game between Montana and Villanova...sure wish the NCAA would keep these big games on Saturday so they don't interfere with a dance party. My sister [in Missoula, MT] will be plugging for the game. The snowstorm, and how soon it hits, introduces a wild card into my decision-making here. Obviously, if it starts snowing by sundown tomorrow, that will tend to influence my decision in favor of the football game...

Posted by: Bombo47jea | December 17, 2009 12:23 PM | Report abuse

Gang, supposed to fly of of Dulles on Saturday. I assume I should shoot for a very early a.m. departure? Any idea if Dulles will be west of the bad stuff?

Posted by: rlbrooke | December 17, 2009 12:35 PM | Report abuse

My thought for my party is increasingly that I will have it start earlier (maybe 330 instead of 7) so people can leave before dark if they want. I will also suggest taking Metro (I can pick people up from Metro in my 4x4) and offer to let people to stay the night.

Unless it is truly a huge storm, I think that may work in lieu of doing it Sunday =).

Posted by: jahutch | December 17, 2009 12:35 PM | Report abuse

Count me among the crowd trying to wish this storm out to sea. Have company coming to town and tickets to the Bears game in Hershey on Saturday. The 2003 storm was so bad up there that they went ahead and let us trade the tickets for a game later in March, but I'm not so sure it will work out that way this time...

Posted by: ValleyCaps | December 17, 2009 12:35 PM | Report abuse

I love snow, too, but , we are leaving town out of BWI on Sunday. We'll see.

Posted by: celestun100 | December 17, 2009 12:39 PM | Report abuse

Is it safe to say the storm has been trending north from each preceding prediction? It looks like from the graphic, that we are on the border between a big event and a minor impact.

Posted by: rocotten | December 17, 2009 1:07 PM | Report abuse


The latest data we have would suggest Dulles will not miss this storm, and it will probably be snowing early Saturday morning. Expect the possibility of delays, unless the storm makes a big move to the east -- it's possible, but looking less likely.

Posted by: CapitalWeatherGang | December 17, 2009 1:09 PM | Report abuse

I have a dumb question for everyone. If it is supposed to snow for 24 + hours which I have heard, then wouldn't it seem logical to expect more than 3-6 inches? Or is it just supposed to be a light snow producer? Surely we aren't even discussing a blizzard potential are we?

Posted by: authorofpoetry | December 17, 2009 1:10 PM | Report abuse

authorofpoetry, I was thinking the same thing. If it stays put, sounds to me like it's going to DUMP.

Posted by: MKoehl | December 17, 2009 1:17 PM | Report abuse

author, I think you will see some revised numbers from the CWG at their next update after they have reviewed all recent data.

Posted by: jpl1019 | December 17, 2009 1:23 PM | Report abuse

authorofpoetry, some pro mets are saying this could be "epic" for DCA/BWI. I suspect the CWG and others will up their range to at least 6-12.

Posted by: worldtraveler | December 17, 2009 1:27 PM | Report abuse

I am getting very excited. I can't wait to get the return on my snowblower investment from 6 years ago! I am a die-hard snow lover and CWG is the BEST.

Posted by: judyusherson | December 17, 2009 1:29 PM | Report abuse

Thanks everyone. As a novice of weather, I am trying to make sense of this discrepancy...

Posted by: authorofpoetry | December 17, 2009 1:32 PM | Report abuse




Posted by: ennepe68 | December 17, 2009 1:47 PM | Report abuse

You guys going to apologize to AccuWeather for lambasting them about their 120 hr forecast, just askin. I understand your forecasting philosophy is to be conservative and not to induce rushes on the grocery store. And I understand that there is a perception that AccuWeather, to use your words, "hypes" storms to drive viewers to their website.

But AccuWeather looks like they nailed this one. And they are also talking about a storm next week. And like I said in an earlier post, as a skier, I find these early warnings valuable whether or not they verify.

Posted by: johnnyd2 | December 17, 2009 1:49 PM | Report abuse

A winter storm watch was just posted for Fairfax County!

Posted by: snowedin85 | December 17, 2009 1:54 PM | Report abuse

WSW is up for the CWA - looking like Sterling is ready to hop on board with a significant event...

Posted by: DullesARC | December 17, 2009 1:55 PM | Report abuse

I like how the quickly storm formed so nicely right at Brownsville, TX today. (That's exactly where the Superstorm formed BTW). We should watch how much it stregthens in the Gulf where the water is still warm and it has lots of energy to work with. I bet this storm starts overachieving beginning now. Or, it's me still wishcasting; we'll see! Bet we'll see watches posted shortly.

Posted by: curtmccormick | December 17, 2009 1:59 PM | Report abuse

Having lived in DC all my life (40+ years), and lived through the big storms of 1979, 83, 87 and 1996, the BIGGEST snow events in DC are whenever a storm comes up from the south and hits a bunch of cold air locked in over us. If the models keep the track of the storm more to the west, you can bet we're gonna get 12+ inches.

Posted by: B-rod | December 17, 2009 2:11 PM | Report abuse

Winter storm watch has been posted:

Kim in Manassas

Posted by: ksrgatorfn1 | December 17, 2009 2:22 PM | Report abuse

Thanks, Gang! You guys are the best. Jason, I enjoy your UVA game forecasts, too. Go Hoos!

Posted by: rlbrooke | December 17, 2009 2:23 PM | Report abuse

Probably for a blog entry not a response post, but could you at some point list out what all the different "models" are and mean? GFS, NAM, 12z, 0z, etc.? And why we should or should not pay attention to them?

Posted by: ah___ | December 17, 2009 2:28 PM | Report abuse

The majority of other blogs to include Easw/x are more on the bullish side of 12-18"

Posted by: TheMot | December 17, 2009 3:26 PM | Report abuse

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