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Posted at 10:25 AM ET, 12/ 6/2010

Any truth to rumors of a Sunday-Monday storm?

By Wes Junker

A possible storm is starting to take shape on the latest weather forecasting models. This potential storm, like many that are almost a week away, is still well west of the U.S. and hasn't even formed yet, so there's considerable uncertainty about the storm's track and what type of precipitation (rain, snow, ice, or some combination thereof) it might bring to the D.C. area and East Coast.

There are a few possible scenarios: 1) a strong storm that tracks toward the Great Lakes region and produces mainly rain east of the Appalachians, 2) a storm that moves into the Ohio Valley and reforms east of the mountains, but tracks inland close enough to the I-95 corridor to keep most of the precipitation as rain, 3) a low that tracks to Tennessee and then reforms off the coast - such a storm would threaten the I-95 corridor with wintry precipitation providing it didn't track too far east into the Atlantic.

At this juncture, is any one scenario more likely than the others?

The first two (the rainier) of the scenarios above are more common during La Nina winters, which is what we're in now, than the third option. However, a strongly negative North Atlantic Oscillation complicates the picture and might leave the door open for the more wintry option.

Last night, the models that were run using observations that were ingested at 7 p.m. EST appeared to be starting to converge on a solution, with the National Weather Service's GFS model trending toward the European Centre model of having one low-pressure area track toward the Great Lakes or Ohio Valley and then reform somewhere just east of the mountains. The GFS was trending from a possible light snow scenario (top left in the image below), to a rain storm (the 168-hour forecast).


Note that both 168-hour model projections had the temperature at 5000 feet at around 5° Celsius (41F). However, a later GFS run (top right) then trended back colder, still probably mostly rain for those living inside the Beltway but not necessarily for those living near or in the mountains. The different model runs shown above probably adequately represent the most likely scenarios with this potential storm, but not every possible one.

The NWS also runs an "ensemble" version of the GFS model, in which the model is run multiple times (at a lower resolution), each with slightly different initial conditions, since there is no way to be sure that the initial observations ingested by the operational model are perfectly accurate and complete, and since small differences in the initial conditions fed into a model can result in increasingly bigger forecast differences the farther out a model is run.

The enormous differences in the various solutions for the potential Sunday-Monday storm (see below) suggest that this is still a forecast with tremendous uncertainty as to the track of the storm, which is critical to predicting precipitation type or amount.

Credit: Penn State University.

At least one ensemble run keeps the low so far south, the Washington area gets no precipitation. Another gives D.C. a snowstorm while others suggest that the storm is a rainmaker. One thing the models do agree on is that there will be some type of storm approaching the East Coast Sunday or Monday, and that it has the potential to be a significant one. Beyond that simple fact, everything else about the storm is just guesswork.

I'm hesitant to try to make any definitive call with such forecast uncertainty, but I'm a so-called winter weather expert so I'll make a stab at it. My gut feeling is that the low will initially track far enough north and west in the Ohio Valley that the Washington/Baltimore area will probably get more rain than snow, with odds higher that it'll be a rainstorm rather than a snowstorm if it's going to be one or the other. However, that's just a guess and not a certainty, and I'm certainly no weather wizard. Besides, the storm hasn't even formed yet and is still just a gleam in Mother Nature's eye.

By Wes Junker  | December 6, 2010; 10:25 AM ET
Categories:  Latest, Winter Storms  
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Next: Snowmageddon - the book!


Thanks, Wes, for taking a stab at interpreting and extrapolating the data! I am not as brave as you ;)

Posted by: Camden-CapitalWeatherGang | December 6, 2010 11:01 AM | Report abuse

This is fascinating because it brings up the question, at what point and where do winter storms start?

Or perhaps the question is, where on the globe do meteorologists start looking?

Is it like a wave or thunderstorms out of Africa, as the first point for tracking hurricanes and tropical systems?

Posted by: jaybird926 | December 6, 2010 11:04 AM | Report abuse


While on an intellectual level I know that there is no reason to take stock in winter storms so far out, the snow lover wants to hear about chance NOWWWWWWW! So thanks, I hope ya'll keep us updated on how the storm progresses across the country, and what that'll mean for us!

Posted by: megamuphen | December 6, 2010 11:11 AM | Report abuse


This is what I like to hear! A meteorologist taking a stab at weather!!!

Right or wrong, I commend you and thank you for giving your best guess about next weeks storm. I wish more mets would do this as well, at least every other day within a week or so of a storm. Who better to do their best explaining model runs and images than meteorologists!?!

Again, thanks for the guesstimation, right or wrong it is appreciated and I hope to hear more from you about this storm and others EARLY AND OFTEN!!!!!!

Posted by: KRUZ | December 6, 2010 11:27 AM | Report abuse

Let me dovetail on jaybird's question. Why are winter storms/noreasters not named a la hurricanes?

Posted by: AdmiralX | December 6, 2010 11:28 AM | Report abuse

Let me dovetail on jaybird's question. Why are winter storms/noreasters not named a la hurricanes?

Posted by: AdmiralX | December 6, 2010 11:29 AM | Report abuse

My own check of the ensemble members for 12/12, per Penn State Met's E-Wall, shows anything from a mixed rain/snow event centered off Delmarva or Hatteras to a low in New England which has passed the area, giving us weather roughly similar to yesterday/today. Ensemble solutions favoring the stormy situation place us far too close to the "540" thickness [rain/snow] line [which seems to run roughly up I-95/395!] for comfort.

Meanwhile the righties at WMAL talk radio seem to have next Sunday's weather all figured out. Their Weather Channel-provided forecast is already saying "fifty degrees with rain".

Posted by: Bombo47jea | December 6, 2010 11:48 AM | Report abuse

If the blocking towards Greenland is still in place, I find it hard to believe that you will have a low pressure cutting up west of the Appalachians. The NAO is negative and it is hard to have GLC's. That just does not make any sense to me. This is where I think the models are wrong.

Posted by: toddlaub | December 6, 2010 12:00 PM | Report abuse

Hey, lets keep things simple:

65% probability - Mixed bag at onset, transition to mostly rain as axis translates to our N.W., ends as s.f.

18% probability - all snow

17% probability - all rain

Posted by: AugustaJim | December 6, 2010 12:04 PM | Report abuse

I would love a major snow event. As far as history goes, what is the accuracy of these models this far out? What about recent storms - where did they start? What were the conditions like?
Knowing what to look for in the models will really help augment my prayers for snow.

Posted by: Bainbridge | December 6, 2010 12:14 PM | Report abuse

hi,i have been following the models on weather advance and i thnink we are looking at a classic east coast snow storm!

Posted by: craneman | December 6, 2010 12:56 PM | Report abuse

Just the possibility of snow makes me super excited whether it flakes out (no pun) or not.

Posted by: Rcmorgan | December 6, 2010 1:08 PM | Report abuse

it's interesting to compare these comments with those of a year ago from 6 days before the december monster storm:

and an SLCB from 3 days before the storm:

interesting that even as of 3 days prior hardly anyone realized what we were in for...

aahhh... good times....

Posted by: walter-in-fallschurch | December 6, 2010 1:30 PM | Report abuse

That forecast is good enough for me. I'm heading for the store to stock up on provisions!

Posted by: ShovelPlease | December 6, 2010 1:44 PM | Report abuse

then there was this:

possibly my favorite post ever... sigh...

Posted by: walter-in-fallschurch | December 6, 2010 1:47 PM | Report abuse

Wes, I've been following you since since the EasternWX forums and always love your insight. Thank you very much!

Posted by: hobbes9 | December 6, 2010 1:59 PM | Report abuse


An actual storm that might develop and affect the Metro area would most likely not be identifiable on the surface charts as a discrete entity before a few days in advance. Depending upon the circumstances it could be located anywhere between the east and west coasts between the northern Gulf of Mexico and southern Canada

Before then, let's say 5+ days ahead, a potential storm is nothing more than a possibility of varying degrees of confidence within the "black box" of forecast models. That potential depends quite literally on the state of the atmosphere (temp, pressure, winds, moisture, etc.) around the entire northern hemisphere. Not surprisingly, there is a multitude of opportunities for the "butterflies" to intervene in the model forecast.

The initial conditions and subsequent developments over the north Pacific are rightly viewed as generally the most directly relevant. But, the developments over the Pacific are in turn dependent, for example, on what's emerging off the Asian continent, which in turn can depend upon just about everything upstream back to the west Atlantic.

Things are clearly a lot more complicated than tracking a disturbance coming off Africa and possibly becoming a hurricane. "

Posted by: SteveT-CapitalWeatherGang | December 6, 2010 2:06 PM | Report abuse

Sorry I wasn't here to comment earlier. I don't see much similarity between the Dec 19th storm and this one. I wasn't here then but do remember noting elsewhere that we were in a period that really gave us a much higher than normal chance of a major snowstorm during that stretch so despite the storm not being on the operational models, the pattern was a more favorable one than this pattern.

As to the negative NAO and blocking. Exactly where the blocking sets up in the Atlantic is important. One feature that is missing this year that was present last year was a deep low near or just southeast of Nova Scotia that provided confluence over New England. That lack is why this storm probably will reform inland rather than off the coast. We don't do well with a low in the OH valley that than reforms inland from the coast. Out towards Winchester or in the mountains might, but not where the bulk of the Washington to Baltimore crowd lives.

Steve, Thanks for answering the question, you did a better job than I would have.

hobbes 9, megamuphen, kruz, Thanks for the nice comments. Same with anyone else who comments. I appreciate the comments whether you agree or disagree with my views

Posted by: wjunker | December 6, 2010 2:34 PM | Report abuse

Wes - once again, great post and appreciate the information. I think it's great you are willing to out on a limb and it sounds like a logical forecast as well. I just wish it wasn't ;). I'll keep reading!

Posted by: parksndc | December 6, 2010 3:01 PM | Report abuse

The ensemble members this morning pretty uniformly ugly if you want snow. Most of the members are strong enough and far enough west to suggest the odds a moving towards a non snow event unless there are a few flakes at onset. However, the storm is only a gleam in the models' imagination so there still is plenty of inherent uncertainty.

Posted by: wjunker | December 6, 2010 3:04 PM | Report abuse

Thanks Steve.

Posted by: jaybird926 | December 6, 2010 3:12 PM | Report abuse

Well, if we do have a snowstorm so be it. Fortunately I just moved to Old Town Alexandria this past summer so if we have snow I will trudge through it, take lots of pretty Christmas pictures along King Street and settle into my favorite pub for a nice winter drink! I am just happy that I won't have to shovel the driveway this winter! :)

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

NWS says 60% chance of rain on Sunday for Jefferson County. If they are that certain 6 days out, it sounds like it'll be a real soaker. Bummer. I got more than enough rain out of the last system.

Posted by: tinkerbelle | December 6, 2010 7:08 PM | Report abuse

all this snow lover can say is nooooooo! I don't like reading about possibilities of snow when I'm scheduled to be in Florida!

Posted by: bachaney | December 6, 2010 8:04 PM | Report abuse

bachaney, tinkerbelle, VAtoLA

It's looking increasingly like an all rain even in the dc area. You probably won't miss any storm being in FLorida this weekend. The ensembles and models are coming into increasing agreement of the western track.

Posted by: wjunker | December 6, 2010 8:57 PM | Report abuse

Oops a typo, it looks increasingly like an all rain event though this early nothing is completely etched in stone.

Posted by: wjunker | December 6, 2010 9:00 PM | Report abuse

Wonderul Post Wes. FWIW this has been in My mind a obvious rain event since saturday dec 4

I am really surprised at the number of folks who think we have a good -NAO in place. We most certainly do NOT.

the current -NAO is RAPIDLY moving out to the East and by DEC 11 is located over Ireland. Thus we end with a classic EAST based -NAO which is very bad news for NE winter storms.

Even worse the s/w goes NEUTRAL over western JS eastern COL and Negative over the central Missi river valley. This is waaaay too far west for east coast winter storms.

Then there is no cold High to the north
nn fresh supply of cold air
no 50/50 Low
south winds ahead of the Low
etc etc...

Posted by: wxrisk | December 7, 2010 12:40 AM | Report abuse


I agree about the blocking in the Atlantic and have expressed reservations about it. Besides the location and orientation not being quite right, we also are missing a vortex near or just southeast of Nova Scotia, we also don't have enough blocking extending across Canada.


Posted by: wjunker | December 7, 2010 8:34 AM | Report abuse

we're having a bit of a discussion about this on the current thread. join us? my questions are about the likelihood of the NAO moving back into the "proper" (for snow) position.

Posted by: walter-in-fallschurch | December 7, 2010 8:45 AM | Report abuse


I posted this on the other thread.

There are two problems with the pattern right now. One is in the Pacific. The evolving position of the vortex over the Gulf of Alaska with low heights pushing into the Pacific Northwest on the longer ranges makes it hard to get a southern stream system going so most of surface lows are coming across the country far enough north that it is hard to hold the cold air over our region. Also, we don't really have a nice vortex in the Atlantic in the proper position. Note in the the 500h forecasts for the Dec and Feb storms last year. Note the difference in the re areas over the Atlantic, the blocking is farther east and the vortex near nova scotia is weaker this year

and compare them with the same type of chart this year.

Blocking often tries to build back west and that is what the models are trying to do on the longer ranges. However, they have been too aggressive bringing the blocking high westward this winter and during westerly QBO years, the tendency is for a more eastward based negative NAO. Combine that with the LA Nina tendency towards a negative PNA pattern and getting a big snowstorm becomes tougher, not impossible, but tougher than a year like last year.

Posted by: wjunker | December 7, 2010 9:43 AM | Report abuse

One factor that none of you seem to be taking into account, even if we do get a west-track up the Appalachians and rain, rather than snow, east of the mountains is the chances for freezing rain/icing at the surface. It may warm up some aloft between now and Sunday, but, in the meantime, we're going to have several more days of cold, frozen-ground. That is not going to be easy to thaw out.

Posted by: MMCarhelp | December 7, 2010 5:15 PM | Report abuse

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