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Posted at 5:30 PM ET, 12/24/2010

Update: Bumping up Sunday snow odds

By Jason Samenow

Snow odds increasing to almost 50/50

Model guidance* this afternoon has shifted the track of the developing storm on Sunday slightly west and closer to the coast. As a result, we think there is a better chance the metro region sees accumulating snow than we did just a few hours ago.

This remains a very delicate situation where very modest shifts in the storm track could make the difference between no snow and 4" or more. Capital Weather Gang's winter weather expert Wes Junker calls this forecast - which has been oscillating all week - "one of the most difficult he can remember." Junker has been forecasting for more than 30 years.

Based on available information, we now believe there is a 40-50 percent chance of at least 1" of snow Sunday, and 25% chance of more than 4". Places closer to the coast including southeast Virginia, the Delmarva peninsula, coastal New Jersey, Long Island and especially southern New England have higher chances of getting snow, with the possibility of very heavy snow and wind.

We'll be examining new model data this evening and will post a short update at 11 p.m.

(*An extra layer of uncertainty is involved in this forecast because NOAA indicated there were some initialization problems with the models this morning. We have not been able to determine whether these problems impacted this afternoon's model runs some of which simulate snowy conditions Sunday)

By Jason Samenow  | December 24, 2010; 5:30 PM ET
Categories:  Latest, Updates, Winter Storms  
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Next: Sunday snow odds continue to rise

Comments

Oh the drama!

Posted by: miglewis | December 24, 2010 5:41 PM | Report abuse

With respect to weather forecasting models, what's an "initialization problem"?

Posted by: snowpro | December 24, 2010 5:43 PM | Report abuse

Man if the Euro goes west tonight start sounding the alarm....WHOOP WHOOP WHOOP WHOOP :)

Posted by: snowlover | December 24, 2010 5:50 PM | Report abuse

@snowpro

It just means the model was run with some data known to be bad which theoretically could bias it a certain way.

Posted by: Jason-CapitalWeatherGang | December 24, 2010 5:53 PM | Report abuse

this is madness

Posted by: deveinmadisonva | December 24, 2010 5:56 PM | Report abuse

Wow, this storm must be so annoying to forecast!

Posted by: samd95 | December 24, 2010 5:58 PM | Report abuse

@deveinmadisonva

Madness?... THIS... IS... WASHINGTON!!!!!!! *Kicks low pressure westward a la Sparta*

Posted by: cleombrota | December 24, 2010 6:09 PM | Report abuse

From the 5:42 p.m. NOAA discussion:

AFTER A STEADY AND INTERNALLY CONSISTENT SOLUTION OVER THE PAST FEW
DAYS...THE 12Z DETERMINISTIC RUN OF THE GFS LOOKS MORE LIKE THE
ECMWF A FEW DAYS AGO. THE 12Z EURO HAS CONTINUED TO TREND TOWARD THE
PREV RUNS OF THE GFS /THE GFS ENS IS EVEN A BIT CLOSER TO THE COAST
THAN THE EURO/. THIS LATEST RUN OF THE GFS COULD CERTAINLY SWING
BACK TO ITS PREV FORM IN THE COMING RUNS - AND ALSO W/ INDICATIONS
OF SOME INITIALIZATION ERRORS...THE ONLY CHANGE TO THE MED RANGE
/FOR THE CWA/ IS A PERIOD OF MORE WIDESPREAD LOW CHANCE POPS ON
SUNDAY.

Looks like the initialization errors may still be in the latest run, but I may be misreading it.

Posted by: NorthFork1 | December 24, 2010 6:09 PM | Report abuse

What time is snow expected on Sunday? Mom has a 7.30 am from Boston to DCA.

Posted by: ADmom | December 24, 2010 6:19 PM | Report abuse

What time is snow expected on Sunday? Mom has a 7.30 am from Boston to DCA.

Posted by: ADmom | December 24, 2010 6:19 PM | Report abuse

Don't forget that the last SREF model run is consistent with the GFS 18zz.

Posted by: MVPlaya8120 | December 24, 2010 6:33 PM | Report abuse

We are planning on driving home to DC from Boston on Monday. Is this a bad idea? Should we leave Sunday night instead? What should we do so we are not driving in a blizzard down 95.

Posted by: allisondt | December 24, 2010 6:43 PM | Report abuse

any models coming out now at 7?

Posted by: samd95 | December 24, 2010 7:00 PM | Report abuse

The way it is looking now, how will it impact eastern NC? (Greenville/Rocky Mount)

Posted by: dbokie1 | December 24, 2010 7:07 PM | Report abuse

Euro will be coming out

Posted by: dan1975 | December 24, 2010 7:08 PM | Report abuse

Supposed to pick up my roommate at the airport Sunday night - told her I'd be fine to pick her up "weather permitting" :P

I know were to keep an eye out at - and that's only here at CWG! Thanks, guys, and to Wes Junker especially!

Re: Wes' comment on it being one of the most difficult storms to forecast - I take that to mean that it was more difficult to forecast than last weekend's no-show?

Posted by: MKoehl | December 24, 2010 7:13 PM | Report abuse

By golly, it's a Christmas miracle

Posted by: nlcaldwell | December 24, 2010 7:13 PM | Report abuse

Regardless of initialization errors in the 12Z GFS, the 12Z ensembles for the surface low positions are tight. I looked at the 984mb contours for 00Z DEC 27 on the "spaghetti" charts. We should see the 18Z GFS ensembles this evening before the 00Z operation GFS run. Like Wes, my career in NOAA/NWS spanned over 30+ years, and this has been the most trying situation I can recall also. Kind of reminds me of the "surprise" coastal storm around 25 JAN 2000.

Posted by: ronbcust | December 24, 2010 7:14 PM | Report abuse

Definetly bringing the snowboots to my parents' house. I might be wrong - but I sort of hope I'm not.

And my aunt & uncle are here from Fresno for the holidays. Wonder what they'll say if the snow pans out? :)

Posted by: MKoehl | December 24, 2010 7:24 PM | Report abuse

MKoehl, Yeah because we kept out pops for big snows relatively low and the swings ended about 72hr before the event when the euro shifted east. This time, the euro waited just as long but now we have two runs of the gfs that have gone west and 30 to 50 percent of the shref members giving us over an inch of snow. There is also likely to be a very tight gradient to the precipitation field meaning that you might not have to drive far to go from 1" of snow to 5". Therefore, minor shifts can make huge changes to a snow forecast. I still think the gfs is the odd man out but I'm not good enough to know for sure.

Posted by: wjunker | December 24, 2010 7:30 PM | Report abuse

what do the latest models say?

Posted by: samd95 | December 24, 2010 7:45 PM | Report abuse

Jason--

Been watching this drama for days, too! Take a look at the difference between the 00z run last night and the 12z run on Thursday. GFS had already moved the .25 inch 60 hour total (valid at 90/78)about forty miles westward between those two runs, from offshore to about Suffolk VA. This morning that progressed to DCA and now it is west of here.

I heard nothing about bad data doing the initial move. We may be looking at evolving continuity rather than bad initialization.

This is mighty interesting...January, 2000?

PJM

Posted by: pmichaels1 | December 24, 2010 8:19 PM | Report abuse

Found an article from that jan 2000 storm. It sounds very familiar.

http://earthobservatory.nasa.gov/Features/Blizzard/

Posted by: MVPlaya8120 | December 24, 2010 8:28 PM | Report abuse

00z NAM is coming out..

Posted by: oriolesfan2323 | December 24, 2010 9:05 PM | Report abuse

The latest NAM has continued the westward shift. Are those initialisation bugs gone yet?

Posted by: cleombrota | December 24, 2010 9:29 PM | Report abuse

00Z NAM a touch west of preceding 18Z NAM but still no precipitation in immediate DC area.

Posted by: ronbcust | December 24, 2010 9:29 PM | Report abuse

00Z NAM a touch west of preceding 18Z NAM but still no precipitation in immediate DC area.

Posted by: ronbcust | December 24, 2010 9:30 PM | Report abuse

0z nam still a miss for the D.C. area. 21z SREF a hit, though, with 5 inches if taken verbatim. But it's unclear whether 21z SREF could still be suffering from the supposed initialization errors this morning (heckuva time for initialization errors). now we wait on 0z gfs to see if the westward shift really was due to bad data or if it was for real. This is the storm and forecast that just won't die! -Dan, CWG

Posted by: Dan-CapitalWeatherGang | December 24, 2010 9:47 PM | Report abuse

Thanks for the update, Dan. I can sense that the staff's frustration with forecasting this storm is similar to my own frustration at making travel decisions due to this "storm".

Thanks for your efforts and Happy Holidays to all of you.

Posted by: ThinkSpring | December 24, 2010 10:05 PM | Report abuse

18Z is not a miss for DCA. Looks like about .70 for 60 hr total. That's likely to be around 10 with expected ratios...IF it is correct (a big "if"!).

Posted by: pmichaels1 | December 24, 2010 10:13 PM | Report abuse

Blue Ridge Mtns report east of Front Royal... 22.1F and cloudy... finished wrapping Christmas presents... TV Channel 9.2 Super Doppler has 97.1 fm Christmas music playing in the background... Some light precip showing up on radar in Warren County... wonder if Eric is seeing anything or if only virga... staying up for CWG update...

Posted by: spgass1 | December 24, 2010 10:17 PM | Report abuse

allisondt, I planned to do the same. Then it looked like the storm would miss DC and head up to Boston instead, so I decided in that case I would head back Sunday (storm is not due up here until Sunday PM). Now it looks like a DC glancing blow and a Boston sure thing, so that might mean leaving a bit earlier on Sunday.

One thing for sure though, I live out in the Shenandoah Valley and always drive 81. 95 is the pits even without snow. My suggestion is the same whether there is snow or not: go inland. Take Tapanzee to 287 to 78 to 81 to Harrisburg, then head south to wherever you need to go.

Posted by: eric654 | December 24, 2010 10:18 PM | Report abuse

Oh geez,

I live in Manassas. So tell me guys; Will I be able to go to work on Monday and then the CAPS game Monday night?

Posted by: CALSGR8 | December 24, 2010 10:24 PM | Report abuse

CALSGR8, Sorry, but you definitely won't be able to go to the Caps game on Monday night. As a matter of fact, no one will be going, because the Caps aren't even playing on Monday. :P

Posted by: oriolesfan2323 | December 24, 2010 10:28 PM | Report abuse

There's got to be more to a forecast - say surface data, radar returns, past experience? - then sticking to the latest model run - with a bias favoring no snow because, well, it usually doesn't snow much around here (last year aside). If CWG has an overall hypothesis beyond the model runs, please let us know. It seems hard to see how you go from "But all in all, chances for snow are decreasing, along with potential amounts" at 3:45 today to "we think there is a better chance the metro region sees accumulating snow than we did just a few hours ago" at 5:30 - unless its based only on the latest model, especially because we know the models have been inconsistent. JB is the frequent target of remarks, but at least he gives a rationale independent of each model run. With a wait-and-see you're never wrong and you're never right. Wes did explain why the forecast for Saturday is only a passing flurry (no moisture feed) - but from DC south it's looking more and more like some accumulation to me.

Posted by: manatt | December 24, 2010 10:38 PM | Report abuse

Hey CWG,

Just curious... if we do see snow on Sunday do we have any idea what time it might start? We have to drive from here to Breezewood, PA and are trying to 'plan' around this as best anyone can. Thanks as always for your awesomeness!

Posted by: Alexandria2009 | December 24, 2010 10:41 PM | Report abuse

Hi SP, sorry I missed your post. I'm not seeing anything at my house since I am 500 miles away from it. But the radar looks to me like most of the activity is drying up as it moves east.

Posted by: eric654 | December 24, 2010 10:45 PM | Report abuse

I was thinking about taking a dump Saturday into Sunday. Should I change my plans? i only ask because I have family coming in to watch. Better to postpon until the latest ukmet comes out?

Posted by: guest7 | December 24, 2010 10:53 PM | Report abuse

0z GFS coming in....looking exactly like the 18z

Snow on the way?

Posted by: MVPlaya8120 | December 24, 2010 10:56 PM | Report abuse

0z GFS gives DC 0.75" QPF through 48 hours.

Posted by: oriolesfan2323 | December 24, 2010 10:57 PM | Report abuse

The 0z GFS looks a little more aggressive than the 18z. Wow.
Unless everything is running with init errors.

Posted by: AndrewRockville | December 24, 2010 11:02 PM | Report abuse

00Z GFS shifts west again. The trend is our friend!

Posted by: bdeco | December 24, 2010 11:03 PM | Report abuse

Looks like 1" QPF....so 10"+ of snow? :D

Posted by: oriolesfan2323 | December 24, 2010 11:04 PM | Report abuse

@ guest7 - Stick to plan A. Your family would be so disappointed.

Posted by: FIREDRAGON47 | December 24, 2010 11:04 PM | Report abuse

guest7--

Great question.

Be sure to post it twice and be as specific as possible for your own personal needs.

Posted by: AndrewRockville | December 24, 2010 11:05 PM | Report abuse

00z GFS shows ~1 foot for us and double that in delaware over the next 60 hours! WOW! http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/00/index_p60_l_loop.shtml

Posted by: samd95 | December 24, 2010 11:06 PM | Report abuse

Don't look now, but the 00Z GFS shifted...you guessed it...further west. It shows 3-6 inches all the way into West Virginia and 5+ from Leesburg to DC and DC and points east 8+. Baltimore/Philly/New York/Boston all get hit with 12+ plus.

Posted by: 4seams | December 24, 2010 11:07 PM | Report abuse

@Guest,
I'd wait if I were you, but stock up on extra TP just in case.

Posted by: JDK4 | December 24, 2010 11:08 PM | Report abuse

Due to the cold weather could we expect 12:1/15/1 ratios?!?!?! but wow this is crazy!

Posted by: samd95 | December 24, 2010 11:09 PM | Report abuse

We should all be at the grocery store buying all of the milk!

Posted by: Alexandria2009 | December 24, 2010 11:10 PM | Report abuse

That's three runs in a row. As of now it appears Berk and Bastardi may have been right for sticking with this one! Could be 8-12 for the Baltimore area.

Posted by: DLO1975 | December 24, 2010 11:12 PM | Report abuse

@manatt

When you're talking about a gradient so sharp that 60 miles is going to make the difference between a dusting and a 6"+ - no physical reasoning is going to help with the forecast... it comes down to randomness, timing and chance. JB's arguments won't change that and if you read between the lines, he's hedging like crazy too. That's why we give probabilities.

Posted by: Jason-CapitalWeatherGang | December 24, 2010 11:14 PM | Report abuse

CWG...
Dont want to be annoying but when is the new update coming out??

Posted by: fortheglory | December 24, 2010 11:15 PM | Report abuse

geez..have to drive to Shenandoah Nat'l. Park Monday morning...perhaps I should leave first thing Sun. morning?

Posted by: BH99 | December 24, 2010 11:15 PM | Report abuse

Great, now i'm going to spend my christmas staring at vorticity maps all day...

Posted by: Brian-CapitalWeatherGang | December 24, 2010 11:16 PM | Report abuse

Methinks guest7 stumbled onto the wrong blog...can someone from CWG direct him elsewhere?

Posted by: natsncats | December 24, 2010 11:16 PM | Report abuse

It's past 11! I demand an official update to hear what the pros think about this storm!

Posted by: samd95 | December 24, 2010 11:17 PM | Report abuse

Tom Sater on WUSA9 just said we will be lucky to get 1-2" on Sunday.

Posted by: oriolesfan2323 | December 24, 2010 11:19 PM | Report abuse

would be nice to get an update..plz!!

Posted by: BH99 | December 24, 2010 11:21 PM | Report abuse

Veronica Johnson on NBC4 said a coating to an inch.

Posted by: natsncats | December 24, 2010 11:21 PM | Report abuse

everyone hold your horses. This controversy over input error remains unsolved. I'm just as excited as you all are but the other models still paint this thing off the coast and until I hear resolve of the issue and a clean bill of health for the new 00z I'm not going to get my hopes up AGAIN for this thing

Posted by: bbirnbau | December 24, 2010 11:21 PM | Report abuse

It's Christmas Eve, folks. Let's give them a break here, they'll have it up when ready.

Posted by: amorris525 | December 24, 2010 11:21 PM | Report abuse

Topper Shutt just said the same on channel 7. I am now completely confused. Can the snow gods just MAKE UP THEIR MINDS PLEASE???

Posted by: kiaraaine | December 24, 2010 11:22 PM | Report abuse

@manatt

Disregarding for the moment that the 3:45 quote is from the comments section, not an official forecast from one of our posts, we have been quite purposeful in *not* making forecasts based solely on the latest model run. It should be clear to anyone who's followed us this week that we have made a concerted effort - as models have fluctated from big snow, to no snow, and back again - to base our forecast on analysis of the latest model run, previous model runs, the overall evolution of models, our past experience, etc. There's no bias toward no snow here. There is a bias toward digesting all available data and leveraging our team's experience to produce a reasoned forecast that doesn't fluctuate as dramatically as models do and is as useful to our audience as the science allows. -Dan, CWG

Posted by: CapitalWeatherGang | December 24, 2010 11:22 PM | Report abuse

TV mets are hedging their bets too.

The fact is we have the GFS giving us a home run, and the NAM still giving us a dusting. With that kind of inconsistency, there's no real forecast to give, except "it will snow, unless it doesn't."

It would be nice if the TV mets at least conceded the uncertainty a bit more instead of throwing out "1-2 inches".

Posted by: JTF- | December 24, 2010 11:24 PM | Report abuse

Tom Sater meant that the snow haters would be lucky, because we are probably getting a slizzard blizzard!

Posted by: samd95 | December 24, 2010 11:24 PM | Report abuse

Looking at the precip map for the 00z forecast I'm not seeing a qpf of 1" like people are saying. Is my model wrong or something? I'm not looking at numerical data but it seems to me like a glancing blow.

Posted by: bbirnbau | December 24, 2010 11:26 PM | Report abuse

They just don't know yet. It's ok.

Posted by: FIREDRAGON47 | December 24, 2010 11:27 PM | Report abuse

Update is coming very soon. The 11 p.m. target was probably a little early since GFS doesn't come in until right at 11 or so. So we needed a little time to digest that.

Posted by: CapitalWeatherGang | December 24, 2010 11:28 PM | Report abuse

Posted by: JTF- | December 24, 2010 11:28 PM | Report abuse

I feel like my site provider for my models is just slow or something. I WANT TO SEE WHAT YOU'RE SEEING

Posted by: bbirnbau | December 24, 2010 11:28 PM | Report abuse

Given that other models have consistently held firm and kept the storm off the coast, I'm gonna continue to take the GFS with a grain of salt.

It's never been at the top of my most trusted model list anyway.

Posted by: ThinkSpring | December 24, 2010 11:28 PM | Report abuse

New update is up. Sorry it took a while longer than I expected. Had to chat with Dan and Wes about the latest output.

Posted by: Jason-CapitalWeatherGang | December 24, 2010 11:33 PM | Report abuse

At this point it's whatever happens, happens. Be prepared either way. Merry Christmas to all and to all a GOOD NIGHT! :)

Posted by: Rcmorgan | December 24, 2010 11:38 PM | Report abuse

I've been reading and loving CWG for about a year now and I have to say following this storm has been the most fun...even including the big ones last year! The roller coaster of emotions has been ridiculous, and now it looks like it might have a happy ending. 6z NAM looking good if not better than 0z GFS...only time will tell. Thanks CWG for staying on top of this...unlike local mets, TWC, even NWS.

Posted by: me4orioles | December 25, 2010 3:05 AM | Report abuse

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