Latest snowstorm to arrive Tuesday night

Jan 10, 2011

Capital Weather Gang chief meteorologist Jason Samenow will be online Monday, Jan. 10, at 2 p.m. ET to discuss the approaching snowstorm which is forecast as a light to moderate snow event with 1-4" most likely across the metro region.

Any theories as to why we keep getting skirted this year? My daughter is SO anxious to build a snowman and go sledding and these piddly dustings are creating big disappointment in our household! Fingers crossed for a bigger than expected snowfall this time around . . .

A lot of it has to do with the La Nina storm track.  During La Ninas, storms along the northern jet stream tend to dominate.  So when they get to the East Coast and redevelop, they do this far enough north that we just get skirted.  The happened on 12/26 and looks to happen tomorrow, but to a lesser extent.  I think we'll see some more snow this time around.

Will I get out of work?

Depends on your work's closing policies.  We're expecting 1-3" from DC and to the west - mostly late afternoon Tuesday and Tuesday night, and 2-4" just east of D.C.  Is that enough to close your office Wed? 

For the five days before the last storm, we were being told that it could take two routes and it would depend on which model was right. If the storm moved east or west would determine whether we would get lots of snow or none at all. I understand that it's impossible to know this stuff 5 days out, but Fox5 was still talking about 2 models THE DAY OF THE STORM. By that time it probably was better to just look out the window than "forecast." Can you explain why "this storm" was so much more difficult, or did everybody just have the holidays off.

The 12/26 storm - which crushed the coast but just grazed us - was a really tough one because we were right on the edge.  Just the slightest shift west would have meant more snow for us.  That looked to be the case 5 days out and never really changed.  When it's such a close call, you're right: when you get within 12-24 hours, your best bet may be to look out the window.  But that was about as close a call as it gets around here.

This storm is a close call, but we're not as  close to the edge.

I'm flying out of Dulles around 8:30 a.m. on Wednesday. Should I expect delays due to the storm, or are we most likely expecting a manageable amount for relatively smooth travel? Thanks!

By Wednesday morning, the snow will have long ended (it should wrap up by 1 a.m. Wednesday morning or even sooner).  Having said that, there may be backlash delays from snow between Philly and Boston - depending on where you're traveling.

It appears that prediction snowfall totals is still an inexact science. How accurate do you believe current models are? Has there been statistical analysis of the models compared with actual snowfall?

Forecasting has made remarkable progress since the 1970s and, in general, forecasts are pretty accurate to 48-72 hours.  But despite these advances, snow forecasting is still challenging and, yes, in exact ... especially in D.C. where there are so many variables to consider.

Regarding statistical analyses, there have been a lot of studies which have looked at the accuracy of the different models.  These studies help us know which models are more skillful than others.

Do you think we will get " or more accumulation area-wide this winter?

So far this winter has been drier than average and we don't see any strong signals this is going to change.  On the other hand, it has been colder than average and looks to remain that way for a while. That means when weather systems come through - we should have some more shots at snow.  February is usually our snowiest month.

What do you think the chances are that Fairfax County gets enough to close on Wednesday? Thanks!

I'd say 50/50 chance based on our latest forecast.  We think there's a good chance you'll at least have a delay.  Do your homework to be safe...

Is our lower totals because of a dry slot or is the Low Pressure gaining strength off the East Coast?

Yes.  We're likely to be impacted by a dry slot as low pressure to the west weakens as it approaches and skips over us to form a new area of low pressure offshore.  It will take a while for the low pressure offshore to get going and throw snow back at us. 

So, on the FreakOut Meter this storm is a nothing to worry about?

Yes.  I wouldn't freak out about this storm.  It may look impressive for a time tomorrow evening, but it will be pulling away just as it's starting to get its act together.

How about the Fredericksburg area?

We've got Fredericksburg in our 1-3" area in our accumulation map.

I am trying to understand how computer models are used for weather events. Are they based on previous weather trends, etc. I know that this question is board so I just wanted a basic understanding of it. Am I on the right track?

Computer models are based on mathematical equations that describe processes in the atmosphere.  Here's a good basic overview: Model basics.

Is Prince George's County, expecting the low end of snowfall total or the high end.

If you're in northern PG county, I think you're at the high end of snowfall amounts - so probably 2-4" rather than 1-3" forecast for west of DC.  If you're in southern PG, probably 1-3".  The further northeast you are with this storm, the more snow you're likely to get.

Hi Jason, Is there anything especially unique about D.C.'s geography that makes winter weather prediction notoriously difficult? I was in Pittsburgh for college and it seemed as if there was less variability in forecasting winter events. Though we got more winter weather than here, the forecasts seemed to be my reliable in terms of whether we would see anything or not. I'm just wondering if the Chesapeake or the mountains to the west make D.C. winter weather prediction a more difficult science than such in P'burgh. Thanks! P.S. Since we played like the Deadskins again this year.. LETS GO STEELERS

I think the factors you mention do make forecasting pretty challenging here.  The mountains effect weather systems by squeezing out the moisture but sometimes they help trap cold air at low levels over our region.  The ocean serves a source of a moisture, but ocean storm tracks can be tough to pin down and mild flow from the ocean can introduce precipitation-type forecasting problems during certain storms.  When you combine the ocean and mountain effects together, it can become a mess.

Keep hearing that a slight shift can make a dramatic change. How much of a shift do we need (and which way) to pick up some of the totals? Also, what is the forecast heading down I-81? My son is having surgery Wednesday morning and my husband is going to Blacksburg for it so wondering when tomorrow he should leave. Thanks!

We're not expecting the accumulating snow in D.C. until late afternoon or during the evening.  So the earlier you leave tomorrow, the more likely you'll miss snow in DC.  You may experience some light snow as you head southwest.    

The slight shift would mostly impact the amount of snow we'd get tomorrow evening, which shouldn't impact your plans.  And I think such a shift might only mean we get 3-6" if storm develops more, or less than 1" if the storm develops less.  Not sure the change would be dramatic, even if significant.

I am driving to Norfolk tomorrow for a meeting. My plan is to start my drive right after the monring rush hour finishes. I have been on the Weather Channel web site and a couple of the Norfolk TV stations web sties to get more info about the snow. I keep seeing snow and ice in the forecast. Can you give me an idea of how the drive is going to be? Do I need to adjust the time I leave?

You'll probably run into some precipitation as you head southeast...but it's unlikely to be crippling or severe.  You may first deal with some light snow through central Va. which may mix with sleet and chance to sleet and rain by the time you get to Norfolk.  Allow extra time and be careful, but you should be ok.

Can we be reasonably confident in getting at least a couple of inches in Alexandria? My partner is really excited about the snow - he went out yesterday and bought us each new caps, mittens,  and I would hate for him to be disappointed if we only get a little snow. Ciao.

We think you have a good chance of getting 2 but there's about a 25% chance the snow is less than 1" .  It's all about managing expecations...

Wow, we snow lovers are getting paid back for last winter in spades, aren't we? Back to the classic cyclogenesis just to our north, but to add insult to injury, the south is getting clobbered, too; everyone but us. As for this place being more difficult to forecast than others, the forecasters every place I've lived in the U.S. west coast, midwest, northeast, here) all said their particular locations was particularly difficult to forecast because of the ocean, the mountains, the lake, the gremlins, and who knows what else. Happy new year.

You make a lot of good points.  Every region has its own forecasting challenges.  I do think snow forecasting is particularly difficult in the mid-Atlantic because we're often so close to the rain/snow line and have to deal with so many types of precipitation.

Nothing falling before 10:00 a.m.? A tough call for school systems.

The snow may not get going until the afternoon, which may make the call a little easier...  Wednesday is more likely going to be the challenge.

This has been fun.  We've just posted our accumulation map, frequent questions and more on the Capital Weather Gang blog.  Follow us there for frequent updates as well as on Twitter (@capitalweather) and Facebook.

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Jason Samenow
Jason Samenow is chief meteorologist with the Capital Weather Gang.
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