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Posted at 5:00 AM ET, 02/ 8/2010

Forecast: Remarkable winter brings new threat

By Jason Samenow

Chance of snow Tues/Wed; quieter thereafter

* Winter Storm Watch Tues.-Wed. for most of metro area (map) *
* A closer look at next snow threat: SLCB | Watch out for ice dams *
* Measuring Snowmageddon's depth | NWS totals | CWG snow reports *
* Power outage maps for Dominion Electric | Pepco | BG&E *
* Outside now? Radar, temps & more: Weather Wall *
* News, traffic & storm coverage: Local home page | Get There *

Today's Daily Digit
 
A somewhat subjective rating of the day's weather, on a scale of 0 to 10.
 
6Sun and temperatures near/above freezing to aid big dig out.
 
Get tomorrow's 'Digit' on Twitter tonight

EXPRESS FORECAST

Today: Mostly sunny. 32-36. | Tonight: Increasing clouds late. 12-18. | Tomorrow: Snow and/or sleet likely in the afternoon. 29-33. | Tomorrow night: Snowy and windy, especially from D.C. and to the northeast. 23-28. | A Look Ahead | Get Express Forecast by E-mail

FORECAST IN DETAIL

Our exceedingly snowy winter may deliver another blow Tuesday into Wednesday before we finally get an opportunity to recover late in the week. There is an outside chance one more bout of winter weather impacts the region late Friday into Saturday (again), but current indications are that chances are better we'll remain calm and dry for the upcoming holiday weekend.

Today (Monday): The day gets off to a frigid start (single digits to teens), but the sun will go to work, helping temperatures climb to around the freezing mark, or even slightly above in the afternoon. So everyone should experience some modest melting of the deep snowpack. Winds will be light, from the west at around 10 mph. Confidence: High

Tonight: After clear skies for the first half of the night, some high clouds will likely start to build into the region. It will be very cold yet again, with lows from the low teens in the colder suburbs to the upper teens downtown. Confidence: Medium-High

Keep reading for the forecast through the week...

IMG_6966.jpg
A snowy scene of the Mall Saturday. By CWG photographer Ian Livingston.

Tomorrow (Tuesday): Clouds will lower and thicken during the morning as low pressure approaches from the south and west. By afternoon snow and/or sleet is likely (60% chance) to develop. For additional details, see our Snow Lover's Crystal Ball. Not surprisingly, it will remain cold, with highs 30-35. Confidence: Medium

Tomorrow Night: Snow and/or sleet will change to all snow (70% chance), and may become moderate to heavy, especially east and northeast of the metro region. As the storm winds up, it will turn windy, with winds from north at 15-20 mph, with higher gusts. Confidence: Medium

A LOOK AHEAD

Some snow may linger into the first half of Wednesday, especially to north and east. By afternoon, but for some lingering flurries, everyone should start drying out but it will be windy and very cold. Temperatures will likely be steady much of the day, with highs in the mid-to-upper 20s. Clearing but very blustery overnight, with lows in the teens (wind chills will likely be near zero). Confidence: Medium

High pressure builds into the region Thursday and Friday bringing a welcome stretch of dry weather. A chilly air mass coupled with the snow cover will keep temperatures colder than average, but highs both days should rise above freezing, climbing up towards the mid-30s Thursday and to around 40 Friday. Very cold Thursday night, with lows in the teens to near 20. Sky conditions both days will be partly to mostly sunny skies, with breezy conditions Thursday diminishing by Friday. Confidence: Medium-High

Tranquil weather may extend into President's Day and Valentine's Day weekend. However, we'll need to keep an eye an area of low pressure in Deep South. It should track far enough to the south that it misses our region, but keep checking back. If it were to impact us, it would threaten winter weather Friday night into Saturday. More likely, we'll have partly to mostly sunny skies right on through the holiday weekend, with highs each day around 40, and overnight lows from the teens to low-to-mid 20s (downtown). Confidence: Low-Medium

By Jason Samenow  | February 8, 2010; 5:00 AM ET
Categories:  Forecasts  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   Del.icio.us   StumbleUpon   Technorati   Google Buzz   Previous: Questions linger for Tues/Wed snow potential
Next: The incredible output of Snowmageddon

Comments

CWG, how much snow is expected to the south and west of town, specifically for the Stafford area? Thanks....

Posted by: david_in_stafford | February 8, 2010 5:38 AM | Report abuse

I'm very pleased to hear that the precip will be mostly snow, since that eases my fears about effects of rain -- in any amount -- on my pitched roof. Knock on wood!

Posted by: krosseel | February 8, 2010 7:24 AM | Report abuse

Something to consider for Tuesday night's storm. It has been so incredibly cold since the blizzard, every flake of snow that falls should stick to the streets. With the blizzard, we had several hours of snowfall before anything began to stick. I think this storm will maximize the accumulations out of whatever we get.

Posted by: rginsburg | February 8, 2010 8:03 AM | Report abuse

I think I just saw 6"-12" inches glancing at the tv a few mins ago...that has to be an overstatement...Right? (haha - as I hope it is...this is overboard for me)

Posted by: parksndc | February 8, 2010 8:55 AM | Report abuse

My the comments have died down since the storm....

CWG...how's this shaping up? How'd we go from "Significant snow likely...." to "Questions linger about...." to now maybe light snow, in about a day? Is it that much on the fence?

Posted by: DaveB2 | February 8, 2010 8:55 AM | Report abuse

Here we go again. I hope everyone has had a chance to dig out and restock before the flakes start to fly on Tuesday.

Posted by: irish031 | February 8, 2010 8:57 AM | Report abuse

See below excerpt from the WMATA (metro) website.

This could mean that the Federal Gov't will remain closed Tuesday.

Agree?

"The greatest challenge facing Metro’s track department at the above-ground stations over the last 36 hours is the continuous blowing and drifting of snow and extreme ice build-up along the third rail, which provides electricity to Metrorail trains. If there is a disruption of electricity from the third rail to the train, trains will not be able to move.

Clearing the above-ground tracks is a process that takes several steps. The heavy duty diesel-powered equipment, known as prime movers, clear the majority of the snow and ice from the two-electrified tracks. Once they are finished doing their job on the service tracks, they shift their focus into the rail yards, where hundreds of trains and miles of additional tracks remain under almost two feet of snow. Dozens of railcars were stored in the underground tunnels Friday night to keep them free of snow and ice, however hundreds of railcars had to be stored in the rail yards, where they remain buried.

Once the prime movers are off the rails, trains equipped with de-icing equipment run on the tracks to ensure that the electrified third rail is clear of snow and ice. These trains apply a de-icing agent and they make several sweeps of the tracks. For that reason they are referred to as “polishers.” The next step to prepare the tracks for service is to clear the snow and ice from interlockings or switches, which allow trains to switch tracks, reverse direction or turn around. For instance, if a train becomes disabled, the trains behind the disabled train can only move around it by switching tracks at an interlocking. If the interlockings are not clear of the snow and ice, there is no way to maneuver around disabled trains.

As stretches of track are cleared of snow and ice, and the tracks are deemed safe for moving passenger trains, Metro officials are likely to resume service to above-ground stations in phases."

Posted by: hskwak | February 8, 2010 9:04 AM | Report abuse

Roof collapse at Fire Station 10 in Bailey's Crossroads.

Fire station 8 roof about to collapse.

Roof buckling at Vienna Post Office.

Simply devastating snowstorm...and more to come. We really need to be spared.

Posted by: ThinkSpring | February 8, 2010 9:05 AM | Report abuse

@hskwak

I'm certainly unable to divine when Metrorail service will resume so we can go back to work, but thanks for sharing the insights into how they deal with the snow. That's really an interesting and seemingly awesome process.

Posted by: krosseel | February 8, 2010 9:09 AM | Report abuse

@ hskwak,

I second krosseel's comments on the snow removal description. I don't think the Federal Government will remain closed two days, especially with the President's Day weekend coming up. I'd bet on liberal leave policy for Tue/Wed.

Posted by: Ken_Davis1 | February 8, 2010 9:20 AM | Report abuse

The one thing I have to say about ice jams:

"Oh, dam."

Posted by: bs2004 | February 8, 2010 9:20 AM | Report abuse

CWG - The 12z NAM and GFS have us in the .75-1.0" QPF range. Given the cold air and expected high ratios, shouldn't we be getting prepared for, say, 10 inches or so? I know everyone is skittish, but at 24-36 hrs out, the models are in their zone. They were right the last time, are things so dramatically different today that we shouldn't believe them anymore?

Posted by: worldtraveler | February 8, 2010 9:30 AM | Report abuse

12z gfs isnt out yet but the 12z nam has dc in the 1.25" qpf
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/12/images/nam_p60_066m.gif

Posted by: cjespn | February 8, 2010 9:38 AM | Report abuse

12Z NAM is a LOT more aggressive than the last run. Seems to be moving more in the direction of the GFS.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/12/images/nam_p60_066l.gif

Rain line stays pretty south of DC area. If that stays all snow, it would possibly be over a foot.

This winter is one that never ceases to amaze.

Posted by: JTF- | February 8, 2010 9:38 AM | Report abuse

Still waiting for someone to explain to me how water can weigh more on your roof depending on what form it takes. :)

Rain-soaked snow is clearly denser. So a shovelful of wet snow will weigh more than a shovelful of dry, fluffy snow. But that's just because you could probably hold more water-soaked snow on the shovel. Lift the same amount of water and it'll be the same weight.

If a ton of iron will break a roof, then so will a ton of feathers. A ton is a ton. It'll be one major stack of feathers, I grant you.

It's kind of like the old Galileo/Leaning Tower story. In a vacuum, a feather will drop just as fast as a cannonball.

Wouldn't matter if it was all solid ice on the roof. The bottom line is how much water falls from the sky and how much stays on the roof.

So what we want is snow -- plus wind, to blow that stuff off the roof onto the ground.

Am I annoying or what. My junior high science teacher would be so proud. And annoyed.

Posted by: Groff | February 8, 2010 9:46 AM | Report abuse

You know, I am willing to deal with 3-6", but if we are talking over 10", I am seriously going out to look for a snow blower today. This is getting to be a joke. But it isn't funny.


Kim in Manassas

Posted by: ksrgatorfn1 | February 8, 2010 9:46 AM | Report abuse

NOOOOOOOOOOOO!

Seriously, where are we and road crews gonna put this snow?

Posted by: ThinkSpring | February 8, 2010 9:47 AM | Report abuse

Groff:

It isn't that a ton of rain weighs more than a ton of wet snow, but that the rain obviously runs off the roof while the snow stays and retains whatever weight it has - particularly bad when it's concentrated on a flat roof.

Posted by: bodypolitic1 | February 8, 2010 9:50 AM | Report abuse

@bodypolitic -

Yeah, I didn't state the context.

I'm responding to the view that we'd be worse off if Tuesday's precipitation was rain or sleet instead of snow.

I'm saying it might be harder to remove wet or icy snow.

But it won't be any heavier, ounce for ounce.

The question is just how much water stays on the roof. In whatever form.

Posted by: Groff | February 8, 2010 9:57 AM | Report abuse

@DaveB2

The runs from overnight were leading me in the direction that this would be a moderate event for the District, bigger event to the north and east, and light event to the south -- but that we could still easily swing to a bigger event or a lighter event. Almost every event this winter has swung towards "bigger" so why am I not surprised the latest NAM (12z) suggests that? Having said that, these scenarios when you have a coastal transfer from a northern stream wave are very, very tricky, I'm not entirely sold on the NAM run...

Posted by: Jason-CapitalWeatherGang | February 8, 2010 10:06 AM | Report abuse

But aren't the GFS and the NAM in line with us getting an inch if cold precip?

Posted by: dustinmfox1 | February 8, 2010 10:14 AM | Report abuse

The reason that snow is more problematic for roofs than the liquid equivalent of rain is because it can't be evacuated as quickly. The majority of problems result from inadequate drainage due to blocked roof drains and ice damming from melting that refreezes. As annoying as 10 additional inches of snow will be, we will be extremely lucky if it all falls as snow. Rain saturating a heavy snow pack on roofs makes in near impossible for it to drain appropriately and leads to structural failures. Although we are not above freezing right now, the sun is melting some of the snow pack on the roofs which will make room for the additional inches we are expecting. This winter has been a nightmare, and I'm so sorry for all the wishing I did last fall for a snowy winter!!

Posted by: klh84 | February 8, 2010 10:16 AM | Report abuse

Thanks Jason!

Exactly the kind of commentary that helps me understand the thinking behind these dynamic forecasts. I know it can be tough processing the variety of data you get and CWG always does a great job!

Posted by: DaveB2 | February 8, 2010 10:33 AM | Report abuse

@Kim in Manassas, go out now and look for a snowblower!!

@ThinkSpring 9:47 am, my words exactly!

Posted by: Murre | February 8, 2010 10:35 AM | Report abuse

Back to the snow/rain/weight question. A unit of water weighs the same whatever form it comes in, but rain falling on snow gets trapped in the snow and just adds to the weight, and that's the problem. If it then goes below freezing, you're stuck with a heavy mass, whereas pure snow can blow or slide off the roof and pure rain drains off the roof.

I dread to think what MY roof looks like right now.

Posted by: doubtingdavid | February 8, 2010 10:39 AM | Report abuse

I like how in a snow/power emergency, the Old Fart Network -- the cohort that still has Plain Old Telephone Service and nonrechargeable batteries -- springs into action. Deriding their wired kids. Sigh, it's a dirty job, but someone has to do it.

Posted by: Groff | February 8, 2010 10:44 AM | Report abuse

@ThinkSpring, thanks for bringing up the news of the roof collapse at Fire Station 10.

Is this what you snow lovers really want? More disruption in the delivery of emergency services? This is one of the busiest firehouses in Fairfax County. This means that response times will only be further delayed, as fire stations in areas farther out are now having to respond over longer distances to cover emergencies in Bailey's.

Posted by: natsncats | February 8, 2010 10:51 AM | Report abuse

Hi Jason,

Still trying to learn from the CWG and everyone else who has been around for a long time but it looks like GFS is confirming another hit for the NOVA/DC/MD area with sizable winds! On a side note I'm working on my master's thesis this winter which is on weather modification technology and applications for the military. We've had so much snow I'm starting to mix up the number of pages I've completed with the number of inches of snow in the last week...was that 22 pages or 22 inches! :)

Posted by: snowedin85 | February 8, 2010 11:04 AM | Report abuse

@CWG - Both the NAM and GFS now have us over a foot out here in the Odenton/Crofton area -- when is the next accumulation update coming?

Posted by: snowlover | February 8, 2010 11:10 AM | Report abuse

SnowMas, no Mas!

To borrow from Mr. Duran (the boxer, not the singer) :-)

Posted by: Paladin7b | February 8, 2010 11:23 AM | Report abuse

Can someone hook me with a link to the GFS and Nam models? Also, when you guys say "The models give us an inch of precipitation..." How do you compute that? Just add up the precip (indicated by color) for each hour of the model?

Posted by: PoorTeacher | February 8, 2010 11:27 AM | Report abuse

All you snow haters out there - I will be here every day in the Spring/summer holding YOU personally responsible for every lightning strike that sets a house a on fire, every heat-related death, every flood-related disaster and see how you like it.

Grow up, please! No one here "hopes" for roofs to collapse, for people to be without power. No one's rejoicing in other people's misfortune. Stop blaming us for it. We like snow. We like winter. YOUR preferred season has its own meterological disaters associated with it. You can't have nice weather and springtime and rainbows and unicorns without heavy rains and thunderstorms. Sorry - snow causes its own kind of problems for people.

If you're offended I would suggest that you want those kinds of bad things to happen to people in the spring - elderly people to die alone from heat-related stress, children to be swept away in rushing rivers - good. Now you know how we feel when you make your unfounded, irrational accusations.

Put your head under your covers for another 6 weeks and wait for your beloved Spring. Quietly, please.

Posted by: DaveB2 | February 8, 2010 11:30 AM | Report abuse

Posted by: ZmanVA | February 8, 2010 11:32 AM | Report abuse

Well said DaveB2.

Posted by: bhfairfax | February 8, 2010 11:34 AM | Report abuse

And before the snow haters start complaining that the snow lovers never offer to shovel them out, I'd like to point out this snow lover spent all yesterday morning and part of this morning shoveling out several neighbors and loved every minute of it. :)

Posted by: ml2152 | February 8, 2010 11:41 AM | Report abuse

Not sure where anyone would get the leap from a snowlover wanting it to snow to a snowlover wanting the roof of a firehouse to collapse...that's some really interesting thinking/or not. Hey Jason, since many of these storms have trended to moving north as they near the time of arrival, would you suppose that Prince William County might be taken out of the Winter Watch?

Posted by: manassasmissy | February 8, 2010 11:53 AM | Report abuse

A UPS delivery person left Laurel at around 3:40 a.m. At around 9:45 a.m. I saw this update on the UPS tracking site: Emergency Conditions Beyond UPS' Control.

Someone at work told me fresh produce is getting hard to find at the grocery.

Sandra in Rockville

Posted by: populationtrends | February 8, 2010 11:55 AM | Report abuse

@PoorTeacher: The models can also be found here:

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/

The easiest to understand columns are the "850mb Temp, MSLP, 6hr Pcpn", which shows the precip during that 6 hour period and the rain/snow line (0 celsius), and the "Total Precip" columns. As a rough guide, 1 inch of rain equals about 10 inches of snow. That can vary, of course, depending on the temperature. Usually colder temps mean higher rain to snow ratio.

Posted by: JTF- | February 8, 2010 11:56 AM | Report abuse

Muchos gracias Zman y JTF.

Posted by: PoorTeacher | February 8, 2010 11:59 AM | Report abuse

NBC4 just showed 8-12 for the Northern Shenandoah Valley a bit less for DC.

Sheesh (too much snow)....

Posted by: spgass1 | February 8, 2010 12:01 PM | Report abuse

Snow my god!

Posted by: shoeflypie | February 8, 2010 12:33 PM | Report abuse

Jason/CWG - Any idea as to the liquid-snow ratios on this storm? I am guessing that if the storm is of a coastal nature, it will be heavier, and more likely to stick to trees and power lines again, but hoping that with the extra wind and slightly cooler weather, that more of it may end up on the ground, rather than held in trees, roofs and power lines?

Posted by: vtavgjoe | February 8, 2010 12:57 PM | Report abuse

Uh-oh. I just saw on WUSA TV that sleet might mix in early tomorrow evening/night in D.C. and the suburbs. Also, the map on Accuweather.com, now shows a mix through NJ. Anyone else seeing this/thinking this? Thanks. David

Posted by: dg33 | February 8, 2010 1:08 PM | Report abuse

Whoops. Sorry about the accuweather.com map interpretation. The low they were showing was off the Carolinas and labeled Saturday. They are showing a mix from the storm that is supposed to go way south of our area spreading a mix up through NJ. That doesn't seem possible at this point and perhaps it's a mistake. The possibility of sleet mixing in was definitely mentioned, on WUSA, as I said.

Posted by: dg33 | February 8, 2010 1:11 PM | Report abuse

Egads, the snow gods have us in their sights. Perhaps we should truck some of the white stuff to Vancouver for the winter Olympics.

Posted by: populationtrends | February 8, 2010 2:59 PM | Report abuse

Latest NWS Winter Storm Warning for Loudoun (a few minutes ago) has 10-20 inches. What happened to 5-8, etc.? I looked at the models and saw where everyone was getting the 0.5" of precip from. Now it's four times that much?!

Sheesh, if the stores weren't empty Friday, they will be now. Have trucks gotten to any grocery stores today?

Posted by: leesweet | February 8, 2010 3:21 PM | Report abuse

The first few (16) panels of the 18Z GFS are in, and the bullseye is as close to DC as you get. The run looks a little colder, too.

Posted by: wigi | February 8, 2010 5:08 PM | Report abuse

Safeway in La Plata, MD was extremely well stocked at 6:30PM Monday, with only modest number of shoppers. SW announcing sales on items intended for SuperBowl parties on deep sale.

Doesn't look like we got mail delivery today, but I am willing to wait a bit more.

WaPo carrier delivered Saturday, Sunday and Monday issues today.

One I heard the forecast for increasing amounts of snow, I spent the afternoon cleaning the last of the snow off of the deck. Its pretty sturdy, but why take a chance!

Posted by: DrVelocity | February 8, 2010 7:01 PM | Report abuse

Time to read a science fiction story about giant reflecting balloons that heat up the polar regions, reduce the temperature gradient across latitudes and thus the winds that bring us all this abominable snow....

Where is global warming when we need it?

Posted by: MoneyEyer | February 8, 2010 11:02 PM | Report abuse

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