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Posted at 11:05 PM ET, 02/ 3/2010

Update: Confidence increasing in high snow totals

By Dan Stillman

* Winter Storm Watch Friday morning through Saturday evening *
* Help CWG name the storm | Snowy National Mall photos *

The evening computer model data has come in and it supports increasing confidence that: 1) A boatload of precipitation is on the way for Friday and Saturday; and 2) Even if sleet mixes in at times -- this would probably be mainly in the southern and eastern suburbs, though even there the odds of mostly snow are increasing -- total accumulations of around 12 inches or more are a pretty good bet.

Here are the CWG team's metro area accumulation probabilities as of now:

5% chance: Less than 6"
15% chance: 6-10"
40% chance: 10-16"
40% chance: 16"+

Best estimate on start time is between late morning and mid-afternoon, continuing through Friday night and probably well into the day Saturday. Our full forecast posting at 5 a.m. tomorrow will include an accumulation forecast map and timeline. In the meantime, see our forecast through tonight and tomorrow.

By Dan Stillman  | February 3, 2010; 11:05 PM ET
Categories:  Forecasts, Snowmageddon, Updates  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   Del.icio.us   StumbleUpon   Technorati   Google Buzz   Previous: Help CWG name the potential storm
Next: Forecast: Major snowstorm poised to strike

Comments

Local TV mets are really loathe to put some numbers on this thing, and it's almost upon us!

Posted by: ennepe68 | February 3, 2010 11:07 PM | Report abuse

Yeah, local mets are being extra cautious with this one. To them I say grow some balls!

Posted by: PeterBethesda | February 3, 2010 11:09 PM | Report abuse

Now I think attention turns to what schools and employers do Friday. If the start time really is projected to be before noon, and the forecast this certain and this ridiculous, I wonder about preemptive closures. Not sure about the history of doing it here but we saw it in Central PA once in a while.

Posted by: MosesCleaveland | February 3, 2010 11:10 PM | Report abuse

If for some reason it occur as planned, it will be called Hypocalypse 2010...

Posted by: fleeciewool | February 3, 2010 11:11 PM | Report abuse

WhooHoo!!! *Doing Raise The Roof Motions* lol. 16"+!!! YEAH!

Posted by: TheAnalyst | February 3, 2010 11:11 PM | Report abuse

Yeah, the missing word "doesn't" really spoiled that last post - serves me right for being sacrilegious.

Posted by: fleeciewool | February 3, 2010 11:12 PM | Report abuse

Topper led off the newscast saying 10 - 20

Posted by: packyderm2 | February 3, 2010 11:17 PM | Report abuse

Virginia has preemptively declared a STATE OF EMERGENCY for this storm

Posted by: Camden-CapitalWeatherGang | February 3, 2010 11:18 PM | Report abuse

The Temperature is still well above freezing right now and higher than predicted. Is this a bad trend? last storm never began with that period of melting when the first flakes fell...I feel that could cut down on our totals.

Posted by: rocotten | February 3, 2010 11:19 PM | Report abuse

!CALL for FORECASTS!

Phasing streams...negative tilted 5H trof...incredible amounts of Gulf o'Mexico moisture invading the mid-Atlantic...significant comma head / deformation. HPC seems to think a major winter event is in the offing this weekend...so it's high time for Contest #4.

The 11th Annual NEWx Snowfall Forecast Contest is just a fun exercise to see who can make the best synoptic-scale snowfall forecast at first-order stations along the east coast of CONUS.

Enter your forecast at the Contest web site @ http://www.newx-forecasts.com/
Follow the link from 'Enter Storm Forecast.'

Deadline: 10:30 PM EST THU...04-FEB-10

Forecast element: storm-total snowfall
Verification begins: 12:01 AM EST FRI...05-FEB-10
Verification ends: 11:59 PM EST SAT...06-FEB-10

-----

An odd 'Miller A/B'-looking cyclone this go'round... altho secondary coastal development isn't in response to northern stream energy but a second....southern stream short-wave flying east after under-cutting the high-amplitude long-wave ridge along west coast.

Tonight/s NAM puts central VA and the eastern shore back in the running for bonus snows...a possible repeat of last weekend/s heavy accumulation event.

-----

No cost...or fee...or annoying requests for personal information to enter.

If you are issuing your first forecast this year...or you entered the 'season-total' forecast contest...you/ll need to create an account (user name / password / valid e-mail...if you want a copy of your forecast sent to your Inbox).

TQ

NEWxSFC home page:
http://www.newx-forecasts.com/

Web log:
http://newxsfc.blogspot.com/

Posted by: toweringqs | February 3, 2010 11:20 PM | Report abuse

@MosesCleveland

It depends on how much precipitation the School Transportation/Facilities folks believe will be on their roadways at 11 am -12 noon (* Kindergarten and preschool students on the road in this part of the day). They could go for an early closing and still get "credit' for a full instructional day - as long as they get all the students their lunch periods.

I agree, it will be interesting with Loudoun County, as it has more severe weather activity in the Western part of the county in many cases . . . .

Posted by: sullivanva1 | February 3, 2010 11:21 PM | Report abuse

Yeah, NAM is nuts. Second time today showing 2.5 to 3" liquid for the region, and now tossing in a 3"+ for portions of the eastern shore, and keeping temps plenty cold for the duration over those regions.

I think I know why the mets are being quiet. They don't want to throw out 1 to 4 FEET predictions until they are sure that the NAM is an insane outlier, no need for panic, yet they don't want to stab themselves in the foot if we actually get one of these insane scenarios.

I'm a snow lover, but I sure hope NAM is wrong. GFS is bad enough...

BTW: Where's a good source for the EURO? NCEP doesn't have that one.

Posted by: RandC | February 3, 2010 11:24 PM | Report abuse

Time for the DC Storm Chant:

Bread, Milk, Toiletpaper!
Bread, Milk, Toiletpaper!
Bread, Milk, Toiletpaper!
Beer, Beer, Beer!

Posted by: washpost86 | February 3, 2010 11:28 PM | Report abuse

The NAM often runs high with precipitation outputs, so I would not buy it verbatim. That said, the GFS supports pretty high liquid output as do other models. This storm will be full of moisture for sure. Very Dec 19thy.

Posted by: Ian-CapitalWeatherGang | February 3, 2010 11:31 PM | Report abuse

Anybody want to take a shot at applying the "50% Rule" to decipher what the CWG forecast actually is? I think it comes out as: we can "expect" around 12" of snow. No more precise than the TV-guys - all in the 10 to 20, 12 to 18, 12 to 16 range (excpet for Sue (my favorite) who hasn't gone beyond "somebody somewhere in the area could see a foot or more.") Noticed several TV guys picked up on variations of this percentage prediction thing - for the first time as far as I can tell - ugh. At least in the old days a forecast was right or wrong... now everything gets a chance and everbody is right all of the time. I guess we just have to see who had the highest percentage possibility for any particular outcome to measure performance. "I called for a 10% chance and that beats your 5% chance..." Great.

Posted by: manatt | February 3, 2010 11:34 PM | Report abuse

Posted by: RandC | February 3, 2010 11:37 PM | Report abuse

@manatt

We'll have a map up in the morning and you'll see exactly what we're predicting. But your interpretation of our probs is about right. On the probs, I guess we were trend setters. Sorry... :)

Posted by: Jason-CapitalWeatherGang | February 3, 2010 11:44 PM | Report abuse

manatt, I hope you are not frustrated with our statistical forecasting method. Our goal is to communicate as clearly & concisely as we're able. Unlike other outlets, we try to manage expectations responsibly. And in mathematical levels of confidence.

Posted by: Camden-CapitalWeatherGang | February 3, 2010 11:46 PM | Report abuse

At any rate, only 5% chance of less than 6 inches, so we will have a lot of snow!!

Posted by: celestun100 | February 3, 2010 11:50 PM | Report abuse

Hey Gang-

Question about the timing and start of the storm.

I am traveling back from Philly via Amtrak Friday afternoon - getting back in around 6 pm. Do you think I will be able to drive home from U. Station to N. Arlington before the storm prevents it?

Posted by: guild370 | February 3, 2010 11:52 PM | Report abuse

guild370 , I am very concerned about your driving prospects. I hope you can make alternate plans... metro underground to orange line stops (I know it's a pain but..) might be best

Posted by: Camden-CapitalWeatherGang | February 4, 2010 12:05 AM | Report abuse

@guild370

It will probably be snowing when you get in with some accumulation. Do you have experience driving in snow? Does your car do ok in snowy conditions? These are the questions you have to consider.

Posted by: Jason-CapitalWeatherGang | February 4, 2010 12:07 AM | Report abuse

I am totally rooting for big snow (!), but what will happen to the Caps game Friday night if this goes down? I've got pretty sweet seats... do they ever cancel?

Posted by: dcnative71 | February 4, 2010 12:07 AM | Report abuse

@manatt

The trend in the weather industry is to shy away from deterministic forecasts (i.e. it is going to snow 20 inches) more than a day or two out and instead use more probabilistic forecasts (like CWG's). The reason for this is not to protect the forecasters' image, but instead to more accurately convey the threat to the public. Someone going out on a limb and forecasting a specific total before the uncertainty in the forecast has diminished is actually doing a disservice to the public by not discussing the array of possibilities.

As for measuring performance, that can still be done with probabilistic forecasts. For example, does it rain 4 times for every 10 times that a forecaster predicts a 40% chance of rain? Granted, this method can't really be done for rare storms like this one, but it is widely used to measure forecasters' performance in most situations.

With all the 40''+ rumors floating around out there, I'm glad the CWG is being responsible and keeping everyone grounded in reality.

Posted by: WxManMike | February 4, 2010 12:12 AM | Report abuse

hey dcnative71, i'm a native too--yet I actually can't recall what it takes to shut down Verizon Center. It may go on as planned, but conditions after the game will be really bad. (FYI, if you attend in the event that they DONT cancel)

Posted by: Camden-CapitalWeatherGang | February 4, 2010 12:13 AM | Report abuse

@RandC - only place I've ever been able to get the ECMWF is the Penn State eWall:

http://www.meteo.psu.edu/~gadomski/ewall.html

FNMOC used to have it until they (ECMWF) started charging too much.

Camden, as a former 20-yr wx guy, I like the stat form for your amount method. I used that alot when briefing ships/pilots/etc.

Posted by: wxsquid | February 4, 2010 12:14 AM | Report abuse

WxManMike, thanks for the supportive thoughts on probabilistic forecasting

Posted by: Camden-CapitalWeatherGang | February 4, 2010 12:17 AM | Report abuse

wxsquid, glad to have your thoughts too!

Posted by: Camden-CapitalWeatherGang | February 4, 2010 12:18 AM | Report abuse

To give you guys a little hint of what you're in for, tomorrow and tomorrow night (Thursday and Thursday Night if you're reading this on Thursday) we're supposed to have 6-8 inches of rain here in Mobile, AL. When the mets up there say it's moisture packed, believe them. ;) You may not get 6-8" of rain in snowfall, but it has a ton of moisture with it.

Posted by: weatherdudeVA | February 4, 2010 12:32 AM | Report abuse

Any thoughts on coming into DC via Amtrak on Saturday night? (And being able to get home to Alexandria from Union Station?)

Posted by: EBagain | February 4, 2010 12:33 AM | Report abuse

My wife is in Europe on business and scheduled to land at Dulles on Saturday. Told her that she should expect the possibility of staying in Paris a little longer. Meanwhile, my 2-year-old daughter are provsioned and prepared to be snowed in for a while. Our hilly small street is among the last plowed. Told my little girl to expect lots of sledding and hot chocolate. I'm in Cabin John (between Bethesda and Potomac, near the river. My guess is 16". BTW - to all, would highly recommend the CWG's twitter feed @capitalweather. Good stuff.

Posted by: Hawaiiexpat | February 4, 2010 12:36 AM | Report abuse

Speaking as a member of the large public safety sector in the DC area, I'm not thrilled with the prospects of the storm this weekend.

Those of us in public safety will not only be required to show up at work, no matter what the conditions, but we will also likely be required to stay in place for most if not all of the weekend if conditions are too bad for us to make it home. Child care and pet care will be concerns for many, if we are not able to leave the workplace.

We chose this career because we are dedicated to helping others. And we will be there for you this weekend, come what may. I just want to ask people to employ some common sense during the storm, and stay put when the authorities suggest that you do so. If you find that you need help, we will be there -- it just may take us a while longer to get to you.

Stay safe everyone!

/end rant

Posted by: natsncats | February 4, 2010 12:41 AM | Report abuse

Thanks for the CWG response - not frustrating or confusing - I just think it is wishy-washy yet implies false precision, especially when coupled with another limiting "Forecast Confidence Bar." At some point when you add so many disclaimers (we all know it's a forecast that depends on uncertain variables) it only complicates getting a clear picture of what you feel is the most likely scenario. At 5pm did you really think there was a 10% chance of less than 2"? How? It also leads to questions over what was or wasn't "expected" based on the outcome. It's only made worst when you have nearly equivalent percentages for a range of possibilities - like earlier with a roughly 33% chance of 6" or less, 6-12" or 12" or more. I'm pretty sure it will be one of those three possibilities, but the only value it provides is in identifying a broad range of potential outcomes - you could have just as easily said that there's a chance of snow ranging from nothing to more than a foot and we can't be any more precise. NWS (and Bob Ryan's) "statistical forecasting method" may be a little more clear in that it is cumulative. For example, a 90% chance of 6", 70% chance of 12", 50% chance of 18". My preference though is for a forecast of the most likely scenario with a discussion of the rationale and the variables that make it uncertain. I think "12 to 18 inches, lower amounts south and east with sleet" is more clear and concise than precentages over 4 ranges from zero to infinity.

Posted by: manatt | February 4, 2010 12:43 AM | Report abuse

Saturday will be a day the city is shut down. I think that is nearing certainty now. Amtrak and Metro are severely affected during 8" of snowfall in a 12 hour period and we will see that. Airports will likely have ground-stops Friday night through Saturday night.

Posted by: Camden-CapitalWeatherGang | February 4, 2010 12:43 AM | Report abuse

The December Snow Event (choose your own euphamism) was a lot of powdery snow. Based on how this thing is coming in and the fact that there may be some mixing, are we looking at heavy, wet snow? I'm thinking about safety because moving that stuff is much more taxing than the thr fluffy stuff.

Posted by: phanieb | February 4, 2010 1:05 AM | Report abuse

I would think the Caps might try to do something similar to what the Wizards did last Saturday when there was a lot of snow, go ahead and play, but allow folks who cannot get there to exchange their tickets for another game. However, there is a problem with that because Caps tickets are in short supply. Meanwhile, the Wizards told folks who could not make Saturday's game that they could exchange them for tickets to this Saturday's game against Atlanta. THAT game could well be an issue since Atlanta would need to get to town during a blizzard. Then the Caps play the Pens on Sunday at noon on national TV, could also be an issue getting the Pens into town if we get a ton of snow. Whoo boy, what a weekend we have in store...

Posted by: ValleyCaps | February 4, 2010 1:20 AM | Report abuse

The December storm was a fairly low ratio storm averaged out, though surface temperatures were a little colder than say last night so it may have been a little fluffier. This event doesn't look terribly different on the ratio/type level compared to the December one. Determining snow type exactly is difficult beforehand.. especially at this range.

Posted by: Ian-CapitalWeatherGang | February 4, 2010 1:29 AM | Report abuse

Althouh I don't disagree with the forecast, to me both the 0z NAM & GFS look to have less moisture than previos runs? I believe this is the case for the last two runs? Hope it is not a trend? That said it does look a bit colder which will mean less of a mix a potentially a bit higher snow ratios.

Posted by: snowlover | February 4, 2010 1:59 AM | Report abuse

Thought it was interesting that the NCEP model discussion posted at 0140L mentioned that the ECMWF (blended with the SREF) has the best grip on the track, but think that the model runs it too shallow off the coast (not bombing enough)... due to the fact all the models have underperformed in that respect this year.

This makes me think that when it goes deeper, it will bring more moisture in, and meet the forecasted totals.

Now that we are inside what was once termed to me as the "magic 72", the models ought to start getting a better resolution on the moisture.

Posted by: wxsquid | February 4, 2010 3:13 AM | Report abuse

Posted by: cjespn | February 4, 2010 3:43 AM | Report abuse

We get crushed according to the 06z NAM - really looking forward to snow accumulation map!

Posted by: snowlover | February 4, 2010 3:46 AM | Report abuse

I think it should be called the "Snowpocalypse."

Posted by: Magnesium | February 4, 2010 8:43 AM | Report abuse

Snowmageddon....

Posted by: pennquaker | February 4, 2010 10:43 AM | Report abuse

Snow fun?

"For most it's no fun."

Posted by: gary4books | February 4, 2010 10:52 AM | Report abuse

The comments to this entry are closed.

 
 
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