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Posted at 8:00 AM ET, 12/18/2009

Update: Storm could affect Friday evening plans

By Jason Samenow

*** CWG's Accumulation Map, Timeline, FAQs, SchoolCast & More ***

Satellite and radar images of impressive storm gathering steam in the South. Credit: NOAA

* Winter Storm Warning midnight tonight to 6 a.m. Sunday *
* CWG on Facebook & Twitter | E-mail forecast to a friend *
* Outside now? Radar, temps & more: Weather Wall *
* Get There: What you should know about traveling in snow *
* During storm: Submit photos | Tweet reports to #eastcoaststorm *

One of the more uncertain aspects of this storm is when it's actually going to start. Some of our guidance suggests accumulating snow starting as early as between 5 and 9 p.m., whereas other guidance holds back the snow until after midnight. We're taking a compromise approach and expect snow to begin between 9 p.m. and midnight from south (i.e., Prince William, Fauquier counties) to north (e.g., northern Montgomery and Howard counties)...but a little earlier or later wouldn't surprise us.

Be advised that as soon as the snow starts, it should start accumulating rather quickly because the ground is cold and we expect the intensity of the snow to increase steadily once it gets going. Some of the worst road conditions in big storms are at the onset because crews have not yet had a chance to treat the roads. Icy spots often form as the initial snow melts but refreezes as temperatures drop and snow picks up.

If you have plans this evening, please check back later this afternoon when we'll update where the snow is and provide a better estimate on the starting time.

By Jason Samenow  | December 18, 2009; 8:00 AM ET
Categories:  Updates  
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Next: You're invited: Saturday happy hour in the snow


That is funny! I just looked at radar in motion map, and thought to myself that think is cooking. I was going to post and say I am betting that snow will start in the dc area around 6:00pm, but you guys beat me to it!!

Posted by: snowlover | December 18, 2009 8:10 AM | Report abuse

Quick question - Can you take a guess at the QPF-to-snow ratio for this storm? I've been using 1:10 or 1:12, on account of its nature (coastal v. clipper).


Posted by: Sterlingva | December 18, 2009 8:18 AM | Report abuse

Based on the radar, I'm just not understanding how it can hold off that late. I know you folks are the experts and you have been more accurate than Nostradomus but am I really that much of a novice that I can't read radar? To me, it looks like it could start as early as 2 or 3 p.m. I guess it takes awhile to "get warmed up" as I think it was Josh said last night in an earlier post.

Posted by: MITCHRAPP | December 18, 2009 8:19 AM | Report abuse

Say, hypothetically, somebody was planning on renting a car at DCA and driving up I-270/70/68 to get to Kentucky tomorrow morning. Would I - I mean, he - have any chance at succeeding in this endeavor?

Posted by: TheAMT | December 18, 2009 8:26 AM | Report abuse


I'd go with 10:1 ratios for this storm. It's not going to be supercold, and ratios are typically lower with Gulf Coast storms because the snow has high moisture content.


It sometimes takes the atmosphere a while to moisten up so to speak...and at least one model suggests dry air is going to try to hold tough for a while. We'll keep a close eye on this...

Posted by: Jason-CapitalWeatherGang | December 18, 2009 8:27 AM | Report abuse

"I am dreaming of a white Christmas"!!

Posted by: rusty6 | December 18, 2009 8:28 AM | Report abuse

TheAMT: Sure! If you're renting Santa's sleigh, that is. You'd probably make it to KY at some point, but you'll have one hell of a time trying to get there. Tomorrow morning is supposed to be when the storm is really getting going around here.

Posted by: weatherdudeVA | December 18, 2009 8:28 AM | Report abuse

This storm resembles the Superstorm on radar more and more with every loop. That's all I'll say about this. Somebody (who's not on a work deadline today) should fetch that map and compare the two. It's pretty stunning.

The snow will start falling overhead late afternoon but will take a few hours to saturate the air and make it to the ground. Radar won't reflect our reality for a little while at first.

Posted by: curtmccormick | December 18, 2009 8:30 AM | Report abuse

Oh boy! Oh boy! Oh boy!

Minor editorial note: "Affect", not "Effect"

Posted by: ChickenLady | December 18, 2009 8:31 AM | Report abuse

Al Roker called for 24+" for portions of VA on the Today show. Those are higher totals than I've seen forecast elsewhere.

Posted by: spgass1 | December 18, 2009 8:31 AM | Report abuse

Pardon the repost, but I asked this question in the old snow post just as this one was posted.

I have another question (because I like asking questions). Take the weather forecast for Woodbridge. They say 2-4" tonight, 8-12" tomorrow, and "some accumulation" tomorrow night. Is that cumulative, or is that accumulation for the time period? Are they predicting 10-16" plus some, or will it be 8-12 with some change?

Posted by: weatherdudeVA | December 18, 2009 8:35 AM | Report abuse

Does anyone know whether the 5" - 12" of rain that they have right now in Miami will translate into the snow equivalent here in DC? Wouldn't that be 50 to 120 inches of snow if there's the 10:1 ration??? That would be insanity.

Also why is Long Island under a blizzard watch and not DC/Baltimore even if they forecast higher snowfall totals for us?

Posted by: tsqnova | December 18, 2009 8:37 AM | Report abuse


I recommend looking at the Nexrad Radar vs the Doppler Radar when determining when the snow is actually reaching the ground. It'll give you more accurate data since it'll eliminate non-precipitation echoes, clutter, and verga.

Posted by: ZmanVA | December 18, 2009 8:38 AM | Report abuse

Any truth to an old adage "starts out fine, plenty behind."?

Posted by: mchristinaw | December 18, 2009 8:39 AM | Report abuse

Blizzard watch would be for sustained winds at 35 mph or higher...our winds will be no fun, but probably not to that extent although you may see localized blizzard conditions around here from time to time.

Posted by: DullesARC | December 18, 2009 8:42 AM | Report abuse

tsqnova - unlikely. the atmosphere and conditions in MIA are much warmer with much higher levels of moisture. the system is drawing from the GOM down there. so, no, we probably won't get 5" of water (50" of snow).

Posted by: worldtraveler | December 18, 2009 8:42 AM | Report abuse

blizzard watch/warning will probably be posted later today. at least that's my hunch.

Posted by: worldtraveler | December 18, 2009 8:43 AM | Report abuse

It would not be unusual for to get the equivalent of Lake Effect snow as winds increase from the east before the main body of precipitation arrives.

Posted by: SteveT-CapitalWeatherGang | December 18, 2009 8:48 AM | Report abuse

For those asking about the blizzard watch - I posted in last night's running blog that the models are only showing (at most) sustained 15-20 knots; and you need gusts to 35.

Up in the Long Island area, the nor'easter will really kick in and deepen, providing a stronger wind flow up there.

As per the National Weather Service web site, snowfall amounts aren't related to blizzards. Need the snow to blow around, but blizzards are all about wind speed and visibility.

(That being said, I'm sure the news will call it the Blizzard of '09, NWS or not.)

Posted by: wxsquid | December 18, 2009 8:52 AM | Report abuse

What are the chances of my flight actually taking off tomorrow? Is it possible, or will everything get cancelled?

Posted by: nmoses | December 18, 2009 9:01 AM | Report abuse

Thank you for the "heads up" ZmanVa.
I will google that radar and look it up.

Posted by: MITCHRAPP | December 18, 2009 9:04 AM | Report abuse

So, the faster this gets here, does that mean the faster its moving, and thus it should accelerate up the coast, and as result (I hope), bring us LESS snow?

Posted by: oldtimehockey | December 18, 2009 9:07 AM | Report abuse

Can someone tell me why Doug Hill is saying 4-7" likely with some areas south and east potentially seeing a foot... saying it on WTOP and ABC 7 so that's what a LOT of people area hearing. People at work are looking at me funny when I say that we can expect a foot or so... since he is saying 4-7"

seems like he's on the low end of forecasts?

Posted by: markinva | December 18, 2009 9:08 AM | Report abuse

Al Roker's most recent forecast appeared to back off the 24" for VA.

Posted by: spgass1 | December 18, 2009 9:09 AM | Report abuse

Doug Hill is out to lunch on this one.

Posted by: worldtraveler | December 18, 2009 9:13 AM | Report abuse

Why has Accuweather dropped the total snowfall in its 5-day forecast for the area? (this is in the "quick look 5 day forecast) Early today, the little Weather Alarm said 8.2 inches---now it says 6.5.

Please tell me that this is not the DC snow lover's worst nightmare happening again! (And I realize that 6.5 under normal circumstances would be really great news...but not this time, not after all this anticipation and confidence.)

Posted by: lilymama | December 18, 2009 9:15 AM | Report abuse

Is it me, or did the 12z NAM just bury us?

Posted by: worldtraveler | December 18, 2009 9:16 AM | Report abuse

I'm scheduled to fly out of IAD tonight at 10 pm. It's going to leave right? Please?

Posted by: gr1231 | December 18, 2009 9:18 AM | Report abuse

grt1231 - you should not have a problem unless the inbound is coming from ATL or MIA, which might have their own delays today.

Posted by: worldtraveler | December 18, 2009 9:23 AM | Report abuse

That 12z NAM is off the charts. Its the Gheorge Muresan of snow storms...

Posted by: DullesARC | December 18, 2009 9:24 AM | Report abuse

Starting to think 6-12"+ the potential for more may be the best forecast starting between 4-7p.

Posted by: ajfishman1 | December 18, 2009 9:24 AM | Report abuse

ARRRGGH, I wish they'd let me download BUFKIT here at work. I mean it's a NOAA product right?

Posted by: Brian-CapitalWeatherGang | December 18, 2009 9:25 AM | Report abuse

Inbound from SFO, outbound to Rio de Janeiro. So it should work and I'll miss the storm just like Air Force One taking off in Independence Day.

Posted by: gr1231 | December 18, 2009 9:25 AM | Report abuse

People keep in mind there is a chance of a historic storm here. Some models are showing 3in liquid equiv. = 30 in. snow . This is less than 24 hours out, so these models are getting closer to reality.

I think news outlets are understating this storm (for once). This could be crippling the area. With cold air in place, this will extend into next week.

Posted by: Tom8 | December 18, 2009 9:26 AM | Report abuse

CAPx - When can we expect an update on snowfall totals/accumulation map, even if it is to just say nothing has changed? Thx!

Posted by: snowlover | December 18, 2009 9:35 AM | Report abuse

Nice map of potential snowfall from this storm:§ion=attach&attach_rel_module=post&attach_id=175033

Snowfall map from '83:

I admire everyone who is trying to predict this storm, it's on our doorstep and still giving the models problems. Oh, the uncertainty!

Posted by: dprats21 | December 18, 2009 9:39 AM | Report abuse

Posted by: ZmanVA | December 18, 2009 9:43 AM | Report abuse

CWG guys - what is the technical definition of a "blizzard"?

Posted by: someonelikeyou | December 18, 2009 9:50 AM | Report abuse


"In the United States, the National Weather Service defines a blizzard as sustained 35mph (56 km/h) winds which lead to blowing snow and cause visibilities of 500ft or less, lasting for at least 3 hours."

Posted by: dprats21 | December 18, 2009 9:55 AM | Report abuse

Someone, a blizzard must have winds of 35+ mph, and snow, or blowing snow limiting visiblility to 500 ft or less.

Posted by: Brian-CapitalWeatherGang | December 18, 2009 9:56 AM | Report abuse

NWS has updated and upped accumulations for Woodbridge. I almost squealed. 2-4" tonight, 7-11" tomorrow.

Posted by: weatherdudeVA | December 18, 2009 10:00 AM | Report abuse

This blog is driving me crazy--I can't stop reading it to find out what's happening with the snow. And I'm from Rochester, for God's sake!

Posted by: LCFC | December 18, 2009 10:02 AM | Report abuse

Okay, I am heading out to the Library of Congress NOW, so I can get back before the stuff starts falling out of the sky. Then I am locking my door and bundling up.

Posted by: epjd | December 18, 2009 10:03 AM | Report abuse

thank you ZmanVA !! Awesome radar. I see now why it will start later than I thought.

Posted by: MITCHRAPP | December 18, 2009 10:05 AM | Report abuse

This is still looking like one for the record books in the area. Most forecast #s will have to go up today.

Posted by: Ian-CapitalWeatherGang | December 18, 2009 10:05 AM | Report abuse

Weather People,

I'd like to see you guys use more statistics in how you present your forcasts. Many of us understand this, and it would be useful.

For example, presumably the estimate for when the snow will start follows some sort of distribution. Between 5 and 9? What does that mean? Is that 50% of the cumulative distribution?

Your "compromise estimate," effectively the median, is not as useful as a probability-weighted mean. Are the "after midnight" forecasts as likely as the "5-9" forecasts? No? Then please adjust accordingly.

You guys have all the data to do this right, but your tendency to oversimplify things is the reason weather forecasts have such large standard errors.

Posted by: Wallenstein | December 18, 2009 10:06 AM | Report abuse

I-270/70/68 to get to Kentucky tomorrow -- doable. The trick is to get west and then north of DC as quick as possible.

The storm appears to be the Washington-Jefferson snowtrack, a huge, 18th century snowstorm that is recorded in the daily diaries of both Washington and Jefferson. Look at the map and you'll see the line that runs directly through Charlottesville and toward southern Fairfax County. Not as much snow as then though.

The one choice that may make a difference could be picking up the rental at Dulles. I'd bet on service at Dulles over National in snow because the highway crews have more space to work with.

Posted by: blasmaic | December 18, 2009 10:10 AM | Report abuse

LCFC: I am right there with you. No productivity this morning and I suffered through those 'wonderful' lake effect snows as a kid.

To all:
If the snow is not very wet, we are going to have some serious travel issues, blizzard or no, just getting around town! After living in NH and NY for a long time, all I can say is that 20mph winds and dry snow = tough driving. The biggest issue of this type of snow is dealing with drifting across roads. Those drifts can get deep really fast after a plow goes through, and we all know that the plow crews struggle to keep up with smaller storms because there are only so many plows around here. Please be very careful tomorrow, or better yet, stay home if you can.

Posted by: dprats21 | December 18, 2009 10:13 AM | Report abuse


Mitch, this is Irene. Please get back to work and stay focused on your current objective.

What is the best estimate for snow totals in the Langley area on Saturday morning? It looks like I'm going to have head into work so I'm not snowed in at home.

Posted by: IreneKennedy | December 18, 2009 10:21 AM | Report abuse

@theAMT...depending on when you leave for KY, you'll be fine. The 270/60/68 rte from DC to Lexington is about 8 hours, if you get on the road by about 3, you'll have no problems if you're willing to drive straight through. I always drive this route for the holidays, but this year chose to regretting that decision.

Posted by: the_local | December 18, 2009 10:24 AM | Report abuse

Zman, thanks for the radar. I see that it is just entering Roanoke right now!

Posted by: Alexandria2009 | December 18, 2009 10:27 AM | Report abuse

CapWx/Ian - I know that the NAM often has feedback issues in regards to qpf, but now that we are inside about 12 hours why is it being discredited so much? Why isnt this a 2+ inch liquid equiv. event? The NAM does quite well inside 48 hours and has been extremely consistent with the extreme liquid totals...and as we remember it was correct with its higher amounts with our last event.

Posted by: DullesARC | December 18, 2009 10:28 AM | Report abuse

LCFC: Right there with you and dprats21! *points to username* Grew up in Buffalo, lived in Rochester before moving down here. While I usually laugh at snow predictions and panic around DC, the more I hear about this one, the more cautious and nervous I get.

Posted by: BuffaloGal78 | December 18, 2009 10:38 AM | Report abuse

Buff, LCFC, Dprats, Nice to know my upstate bretheren are around!

Posted by: Brian-CapitalWeatherGang | December 18, 2009 10:43 AM | Report abuse

DullesARC, this might be better for one of the meteorologists to answer, but the NAM does have some history of going overboard with precipitation. That said, I don't think it's totally out of its mind. The GFS has been keeping people skeptical but it's falling into line with the NAM (with lower QPF, but still up to around 1.5 and 2" not terribly far off).

It's tough to forecast an extreme event since they are relatively rare.

Posted by: Ian-CapitalWeatherGang | December 18, 2009 10:44 AM | Report abuse

Cwgang- If we had this exact same set of data and model runs in Mid-Feb, do you think the TV forecasters, Capital Weather Forecast etc. would show higher amounts? Is it simply because December doesn't bring 12"+ storms in the DC area that the fcast totals are less than the models indicate?

Posted by: markinva | December 18, 2009 10:50 AM | Report abuse

The 12z GFS is now in agreement with the NAM on QPF. Anyone going to up their snowfall predictions now??

Posted by: worldtraveler | December 18, 2009 11:00 AM | Report abuse

Greetings from another upstater (Rochester), and yes, drifting is the real doozy on the roads, even for those who can drive in winter weather. Between depth, and lack of visibility... BTW, the storms which had us snowbound in Wayne CO NY once a winter weren't from sheer depth (only a foot or so) - they were from the landscape encouraging formation of 8-16' drifts at awkward locations.

Posted by: fsd50 | December 18, 2009 11:07 AM | Report abuse

fsd50: I remember one huge Rochester (Monroe county) storm, after which all the kids in the neighborhood were walking along rooftops in our cul de sac, which we accessed via the enormous drifts. Of course this was the late 60s/early 70s when parents would let us out of the house for hours, as long as we were home by dinner! Maybe the enhanced supervision these days is not such a bad thing...

Posted by: LCFC | December 18, 2009 11:14 AM | Report abuse

I'm tracking the storm, looks light rain in the SW corner of Virginia along the Tennessee border.

Posted by: JW21 | December 18, 2009 11:18 AM | Report abuse

MITCHRAPP and Vazman: just a heads up -there is no difference between Nexrad and Doppler. Nexrad just means "next generation radar", which is what Dopppler is. Doppler is the (radar) effect they use to collect the wind, precip and other data from the lower atmosphere,.

Posted by: johnnyd2 | December 18, 2009 11:19 AM | Report abuse

When's the last time the DC area had a storm (potentially) this big in December? I'm a native, and I remember big storms in January, February (President's Day weekend seems has a big red target painted on it sometimes)and March, but I'm having difficulty coming up with one for December.


Posted by: MKoehl | December 18, 2009 11:22 AM | Report abuse

MKoehl, I checked that myself and the biggest storm in December was on the 17th in 1932 with 12 inches.

Posted by: nlcaldwell | December 18, 2009 11:24 AM | Report abuse

Mkoehl- If the storm materializes per the upper end of forecast this could be the biggest December storm ever in DC IIRC.

Posted by: markinva | December 18, 2009 11:24 AM | Report abuse


I was thinking about that too. I grew up in the Shenandoah Valley, and remember the big storms of Jan and Feb.

I seem to remember a somewhat significant snow around Dec 28th/29th in either '93 or '94.

Nothing like what is being predicted with this storm however.

Posted by: JW21 | December 18, 2009 11:26 AM | Report abuse

Another upstate NY-er here! Went to school in Rochester. Driving home to Utica this Christmas. Might have more snow here than there this year. ;-)

Posted by: CM_in_Fairfax | December 18, 2009 11:27 AM | Report abuse

MKoehl: The last time I lost my ruler in the snow was Valentine's Day 2006, when we got 14 inches of snow here in Lake Ridge (we were only supposed to get 5 or 6). A big storm like the one we're facing last occurred in Feb of 2003, dubbed the Second President's Day Storm (there was another one in the 1920s I believe).

Posted by: weatherdudeVA | December 18, 2009 11:31 AM | Report abuse

Hi, we have a flight to Orlando at 9:00 am from Dulles on Saturday.

While I am excited about the snow, I am worried about flight delays or cancellations. Should we expect to get lucky or should we try to postpone our tickets?

Posted by: RoseVA | December 18, 2009 11:31 AM | Report abuse

@MKoehl Update to my last post, I'm sorry...I didn't see that you wanted December. I remember lots of 1-7 inch storms in December but nothing this big this early.

Posted by: weatherdudeVA | December 18, 2009 11:32 AM | Report abuse

Sorry to say it Rose, but you should probably bring a book and be prepared to wait.

Posted by: Alexandria2009 | December 18, 2009 11:35 AM | Report abuse

roseVA -- I'd call the airline now and see what they can do for you. Could you leave right now if they have seats?

Posted by: Izbit | December 18, 2009 11:35 AM | Report abuse

roseVA - your larger problem may be getting to IAD for a 9am flight.

Posted by: worldtraveler | December 18, 2009 11:51 AM | Report abuse

Thanks, all!

nlcaldwell - that's before my dad's time. (He was born - in Denver - in April of 1932.)

Wow. I'm just going to have to see how this pans out. Wow.

Posted by: MKoehl | December 18, 2009 11:58 AM | Report abuse

Thanks guys. May be I am on optimist, but I keep thinking getting to airport won't be an issue. I only live 5 miles away. I will call the airline but leaving today will be pretty hard for us.

Posted by: RoseVA | December 18, 2009 12:08 PM | Report abuse

I just saw a satellite photo of the storm as it sits in the GOM and it sure looks like a hurricane; even has an eye.

Posted by: worldtraveler | December 18, 2009 12:31 PM | Report abuse


Do you mean the small swirl passing the coast of LA headed for the FL pandhandle? I thought the colorful stuff was the storm...

Silly me.

Posted by: Alexandria2009 | December 18, 2009 12:38 PM | Report abuse

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