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Posted at 5:00 AM ET, 02/23/2010

On the edge of a major storm

By Jason Samenow

Next Chance of Accumulating Snow: Late Wednesday into Thursday
Probability of Accumulating Snow (1" or more): 30%

The amazing winter of 2009-2010 just does not want to let up. The latest model guidance is now suggesting a very powerful storm may develop just to our northeast Wednesday night into Thursday. Though current model forecasts suggest accumulating snow will be to our north and northeast, the simulated snow is close enough that a slight shift could result in major changes to the forecast.

The North American Model (NAM) simulates an extremely powerful storm just south of New York City 7 p.m. Thursday. The metro region is on the southern edge of the precipitation field from this storm.

An area of low pressure developing off the Southeast coast will interact with an intense upper level disturbance swinging through the mid-Atlantic and low pressure over New England. The result of this interaction will be a massive storm -- sometimes referred to as a "bomb" due to its explosive development. Exactly where the storm blows up and its track will determine where heavy precipitation falls. Right now, the heavy precipitation looks to just miss our region, with the biggest impacts northeast of Baltimore -- along the corridor from Philadelphia to New York.

Keep reading for more commentary and accumulation probabilities...

If the storm develops a little further south and west (off the Virginia Capes or Delmarva peninsula as opposed to off the coast of New Jersey or further northeast), accumulating snow would be a higher probability for our region. That scenario is against the odds, but cannot be ruled out.

Even if the storm develops off the coast of New Jersey, it may be powerful enough to drive some snow southward over our region on Thursday and there's a decent chance snow showers will impact the region from the upper level disturbance swinging through Wednesday night. Together these factors could produce some light accumulations, especially northeast of the beltway. Irrespective of snow, very strong winds are likely to develop over the entire mid-Atlantic on Thursday.

Here's my current assessment of snowfall accumulation potential:

Less than 1": 70%
1-3.2": 15%
3.2-7": 10%
7"+: 5%

(What's the significance of 3.2"? Click here.)

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

By Jason Samenow  | February 23, 2010; 5:00 AM ET
Categories:  Snow Lover's Crystal Ball  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: PM Update: Showers quickly moving through
Next: Forecast: Dreary week drones onward


Can you make a guess as to the wind at this point? Are "very strong" winds in the 20's, 30's, or higher?

Posted by: debiguity | February 23, 2010 5:10 AM | Report abuse

I am not wishing for snow but this is a lot closer than the model runs yesterday. I think we need to see a couple of more NAM runs to see if this low bombs out further to the south. The last two NAM runs look consistent but the two runs before had to low further to the north than now. IOW, each couple of NAM runs seem to move the low a little more to the south. This all way close. We could just have clouds or a lot of snow Thursday

Posted by: ntrlsol | February 23, 2010 6:48 AM | Report abuse

well, while it's not the "sure thing" we've had several times this winter, i suppose this is what we get around here: "it might snow, but probably not. OTHER places will get lots, though...."


Posted by: walter-in-fallschurch | February 23, 2010 7:36 AM | Report abuse

What chances do these winds have of affecting air transportation on Wednesday or Thursday?

Posted by: david0071 | February 23, 2010 8:32 AM | Report abuse


Air transportation will probably be ok Wednesday, but by Thursday, I'd expect delays due to wind and possible snow. Also, consider that the storm will have MAJOR impacts on hubs in the Northeast, which will trickle down into the metro area.

Posted by: CapitalWeatherGang | February 23, 2010 8:50 AM | Report abuse

for those snow-i'm-fed-up-with-iters, perhaps you could institute a Rain Lover's Crystal Ball.

i imagine "thinkspring" et. al. have felt kind of left out this winter. they can go all ga-ga about the impending rain, maybe report in when drops start to fall. perhaps they could post comments like "pavement wet here in falls church!!!", and "whoo hoo, everything's shiny in arlington!". they could report on the size and intensity of rain, and where the little rills and rivulets are forming.

over the summer, instead of a "schoolcast" you could have a "BBQcast": 3 burgers means you're probably going to have to call off that BBQ - or at least move the grill under the carport.

alternatively, you could post a SIFUWICB (Snow-I'm-Fed-Up-With-Iters Crystal Ball). just leave it up from april through november or whatever to assure them there is zero chance of snow. maybe you could update occasionally: "still no chance of snow through july".

Posted by: walter-in-fallschurch | February 23, 2010 8:57 AM | Report abuse

CWG, what are you doing to me? Why are you trying to get my hopes up? But I'm going to stay calm, stay calm....I need more concrete evidence before doing the "It's going to snow" happy dance.

Posted by: Rcmorgan | February 23, 2010 9:26 AM | Report abuse

CWG, what are you doing to me? Why are you trying to get my hopes up? But I'm going to stay calm, stay calm....I need more concrete evidence before doing the "It's going to snow" happy dance.

Posted by: Rcmorgan | February 23, 2010 9:39 AM | Report abuse

mOVING Saturday: are you going to jinx that?

Posted by: linda_521 | February 23, 2010 9:44 AM | Report abuse

Keep a close eye on this thing.. big potential still. Seasonal trends should not be ignored.

Posted by: Ian-CapitalWeatherGang | February 23, 2010 10:53 AM | Report abuse

Still waiting on that CWG post explaining the scientific method applied to produce the probability forecasts for snow potential - perhaps an extra paragraph could explain how you have reached a level of precision down to the tenth of an inch of snow in this probability forecast as well - (3.2").

Posted by: manatt | February 23, 2010 11:04 AM | Report abuse

That new GFS appears to bring more precip to VA than earlier iterations.

Manatt, there may be some art mixed in with the science of forecasting. At least the percentages add up to 100 :-)

Posted by: spgass1 | February 23, 2010 11:10 AM | Report abuse

will snow chances be updated here or on the other thread?

Posted by: walter-in-fallschurch | February 23, 2010 11:28 AM | Report abuse

So we might have a briefly blizzard-y Thursday morning....especially north of the city.
How fitting that Mommma Nature would send us one more storm to garnish our already insane Feb. snow totals.

Posted by: FIREDRAGON47 | February 23, 2010 11:34 AM | Report abuse


The 3.2" was sort of thrown in for fun ... as per the link mentioned just below the probabilities.


We'll update the snow forecast in PM Update today pending some of the afternoon model info.

Posted by: CapitalWeatherGang | February 23, 2010 11:39 AM | Report abuse

@Walter: Or a humidity-lovers' crystal ball. Drips of sweat for how miserable it will be (one drip: suits/ties okay; two drips: dress down in short sleeves; three drips: hope you can wear shorts; four drips: bikini time). And mosquitos: 4 is "forget going outside without a DEET bath first". Ah summer. How I miss thee. &_&

Posted by: ah___ | February 23, 2010 12:02 PM | Report abuse

right...the MLCB! lol!

Posted by: walter-in-fallschurch | February 23, 2010 12:05 PM | Report abuse


Re: how we come up with probabilities, we don't have a specific "scientific method" for developing them. We look at the models, the overall pattern, seasonal trends, etc and then we consider the range of possibilities, and assign probabilities to them. So they are based on intuition, experience, and our interpretation of the data. We have gotten plenty of positive feedback on these probabilities, but you clearly seem to object to our use of them. So if you don't find them helpful, ignore them. Or, if you have a better suggestion on how we should communicate uncertain information, please let us know.

Posted by: CapitalWeatherGang | February 23, 2010 12:06 PM | Report abuse

@walter-in-fallschurch, @ ah__,
There is a ND graphic for "Nice Day", meaning: 1) 65-85F, 2) Dewpoint less that 65 (not gonna sweat), 3) mostly sunshine (at least 50%), 4) rain probability low (under 20%). So thinkspring is already covered.

Posted by: prokaryote | February 23, 2010 1:30 PM | Report abuse

Jason: Nice usage of the "3.2" in your probabilistic breakdown.

Posted by: Andrew-CapitalWeatherGang | February 23, 2010 1:45 PM | Report abuse

i've seen that "nice day" graphic and it bothers me in the same way that "daily digit" does. i mean, nice according to who?! admittedly, it's all in fun and for MOST people those probably are the qualifications for a nice day...

and does ThinkSpring like boring weather (as in a "nice day") or exciting, but summer (or spring!) weather like thunderstorms, hail, rain etc...?

Posted by: walter-in-fallschurch | February 23, 2010 1:52 PM | Report abuse

To Everyone posting today: Thanks! This is one of the most light-hearted SLCB threads I have read in a while. (I seem to remember more of these in past years) Very witty. From Jason's 3.2"( and how dare you expect people to click on a link to seek information, lol) to the "BBQ cast"... well done!

Posted by: dprats21 | February 23, 2010 2:16 PM | Report abuse

uhh, crap... what are my chances of not having delays at BWI on thursday morning for an 8:15am flight. i have two layovers (houston and mexico city) before my final destination in southern mexico late thursday night. this isn't just a normal trip... it's my BROTHER'S WEDDING!!!! i have to get to mexico city by 4pm thursday... sigh. stupid winter.

Posted by: dotjeffdot | February 23, 2010 2:25 PM | Report abuse

oh walter, i am among the SIFUWIs, but you are awesome. thank you for making me laugh for several consecutive minutes during an otherwise rather crappy day. "woohoo! everything is shiny in arlington!" -- i'm going to use that one. now here's to those 50+ temps creeping up for the first week of march. BBQ ready!

Posted by: esmerelda123 | February 23, 2010 2:36 PM | Report abuse

Well, the new GFS data sure looks promising...if by promising you like more snow. Talk about seasonal trends..

Posted by: firstweatherman | February 23, 2010 2:39 PM | Report abuse

@walter - I LOVE thunderstorms. Couple of summers ago, was in Corolla when a fierce line of t-storms blew up over the ocean overnight. I spent the night in the hammock on the patio watching it.

So, count me as a fan of that.

Posted by: ThinkSpring | February 23, 2010 2:40 PM | Report abuse

ha! thanks. ;-)

thunderstorms are cool. but, well, they seem kind of dangerous and costly....maybe we'll talk about that this summer....they also seem to cancel a lot of things (swim meets, evenings at the pool, golf) though...

i'd love 'em even more if we didn't lose power so often during a storm. and, of course, i'd love 'em even more if they'd rain snow!

Posted by: walter-in-fallschurch | February 23, 2010 2:57 PM | Report abuse

I like that 5%.

Posted by: ennepe68 | February 23, 2010 3:22 PM | Report abuse

CWG - it's disappointing to see that your only response to fundamental flaws in your communication approach of "probability forecasting" is to say other people "find it helpful" so ignore it if you don't like it. Really? Ok - I accept your explanation - your blog is for entertainment, not sound science or reasoned forecasting. There is no "scientific method" to your probability forecasts, they can't be verified, they can't be repeated, and they reflect nothing more than a group of guys picking numbers they think sound good to them. If it gives the false impression of "precision" where there is none, no big deal. If the numbers don't add up, it's ok - they don't need to. It's all make-believe (which, as you note, illicits lots of positive feedback, so that makes it all ok.) Sorry - I guess I expected more of you.

Posted by: manatt | February 23, 2010 3:25 PM | Report abuse

Winter Storm Watch for Howard County

Posted by: mickb1 | February 23, 2010 3:27 PM | Report abuse

OK, OK, so I'm compelled to quote one of my favorite quotes from Star Trek IV, when Spock has to guess at something and Dr. McCoy explains to him about Kirk trusting that guess:

"He means that he feels safer about your guesses than most other people's facts."

So, CWG, give us your probabilities, your digital digit, and everything else because I trust your guesses more than most people's facts.

(sorry for the geek factor!)


Posted by: ThinkGreen | February 23, 2010 3:34 PM | Report abuse


Why are you being so hard on the CWG? Actually, you are incorrect that their probabilistic forecasts cannot be verified. Any probabilistic forecast can be mathematically verified, for example, by using a Brier Skill Score or Heidke Skill Score. If you want, score the CWG forecasts and report back to us your findings, but you should do that before you start trashing their work. Also, how can you accuse the CWG for giving a false sense of "precision" when their forecasts are probabilistic, not deterministic?

Posted by: AvraminMD | February 23, 2010 3:45 PM | Report abuse

Thinksprng- I guarantee I saw that same storm. Some of the best pictures I have ever taken.

Posted by: Rileymrtn | February 23, 2010 4:24 PM | Report abuse

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