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Posted at 7:30 PM ET, 01/29/2010

PM Update: Accumulation forecast on the rise

By Ian Livingston

Highest to the south; cold continues through weekend

* Winter Weather Advisory tomorrow for D.C. & points south (map) *
* Winter Storm Warning far southern suburbs (map) *
* Outside now? Temps, radar, winds & more: Weather Wall *

Well, the cold sure returned in a big way today, but what about tomorrow's snow? Temperatures today only climbed into the mid-and-upper 20s off morning lows mainly in the upper teens, and just a little sun has not done much here at the surface. The storm system slated to arrive tomorrow is still throwing a curveball or two, but for snow lovers the new pitches are friendly looking ones.

The CWG team's predicted snow accumulations for Saturday (updated @ 3:30 p.m.). Forecast confidence is Medium.

Through Tonight: One word: cold. Evening temperatures in the 20s fall to lows as far down as the middle teens in the cold spots to around 20 in the warm ones. Any breaks in the clouds early will fill in as the night progresses. There's an outside risk of some snow showers by sunrise, but accumulating snow should hold off until the daytime tomorrow.

Tomorrow (Saturday): Living on the edge is never easy, and we still sit pretty close with regards to the snow event for Saturday. It does look increasingly likely the area will end up with some accumulations, which could end up on the moderate side, especially for areas south of D.C.. Snow starts by late morning or midday and continues through evening. The heaviest should be during the afternoon into early evening. Highs could reach the mid-20s if we see less snow or a late start, but may hover closer to 20 as the snow falls.

Accumulation: Computer models continues to bring the storm's precipitation shield north and our accumulation forecasts are on the way up as well. There is still some time for shifts in either direction, so continue to stay with us for the latest. Our best guess for accumulations is shown in the map above. Below are our probabilities for different accumulation amounts (metro area):

25% chance: Less than 2"
40% chance: 2-4"
25% chance: 4-6"
10% chance: 6"+

See Camden Walker's full forecast through the beginning of next week. And if you haven't already, join us on Facebook and follow us on Twitter.

By Ian Livingston  | January 29, 2010; 7:30 PM ET
Categories:  Forecasts  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Slight shift north with snow accumulations
Next: Update: Saturday snow chance solidifying



Posted by: Yellowboy | January 29, 2010 3:42 PM | Report abuse

I really enjoy being able to follow along with you guys as these events unfold - that is what makes this site so great. Some may falsely claim - out of their own inferiority, apparently - that you are "hyping" snow, but what you are really doing is giving us a glimpse into how weather is forecast. And this comes from a snow and cold hater!

Keep up the good work, and thanks to the WaPo for hosting you.

Posted by: SouthsideFFX | January 29, 2010 3:44 PM | Report abuse

omg! falls church get 3" now - up from a dusting to 1" this morning. nice. i'm officially excited again! were still 18 or so hours away from snowdown, and the way this is trending, we could get 6"...

Posted by: walter-in-fallschurch | January 29, 2010 3:54 PM | Report abuse

So according to your probabilities and map, we're triangulating to around 3 inches locally? I'll take that for a weekend snow.

Posted by: PaLun | January 29, 2010 3:55 PM | Report abuse

I think that the National Weather Service is making a mistake with this storm. They have no winter weather advisory at all until you get down towards Fredericksburg. It sounds like they need to issue at least a Winter Weather Advisory for Washington DC and then perhaps a Winter Storm Warning for suburbs to the south.

Posted by: rginsburg | January 29, 2010 4:04 PM | Report abuse

I am liking what I am seeing but as we all know this could change at any moment.

Posted by: justin-N-sterlingVa | January 29, 2010 4:05 PM | Report abuse

My neighbors have parked facing out and there are some people (at the bank and post office parking lots) acting a little crazy. Maybe we will get snow!!

Question: Are there particular cloud patterns or other signs that we could use to predict a storm if there were no radar, etc.?

Weren't people able to predict a bit by looking at the sky in the old days?

Posted by: celestun100 | January 29, 2010 4:10 PM | Report abuse

@ celestun--if they're parked, they're not crazy. If they were crazy, they'd be at Safeway/Giant clearing the shelves of milk and toilet paper.

@Yellowboy. And lamest!

Posted by: ah___ | January 29, 2010 4:21 PM | Report abuse

Wishcasting works!
I'm really wishing for a WEEKDAY storm - Tuesday looks good.
I hope Bastardi at not so accuweather is right!
Keep these updates a comming.

Posted by: Bainbridge | January 29, 2010 4:22 PM | Report abuse

wow. noaa does not believe in this storm. predict less than one inch for pretty much all dc metro area

Posted by: samdman95 | January 29, 2010 4:23 PM | Report abuse

ah__ Just to be clear, they were on their way into the parking lots. I think they were in a hurry so they could get their supplies!!!

Posted by: celestun100 | January 29, 2010 4:25 PM | Report abuse

Celestun100 - totally ROFL laughing at the "neighbors parked facing out" obeservation. I know that the five sets of Baby Boomer neighbors on our cul-de-sac (my wife and I are the token Gen-X'ers) are buying all of the snow hype when they all park facing OUT on the driveways -- and they're ALL doing it this afternoon! ;)

Posted by: VAStateOfMind | January 29, 2010 4:31 PM | Report abuse

It is funny, although to be fair, given the December storm, I can't blame them.

The snowplows tend to clear the street, but leave ridges of snow behind the cars.

A lot of the town homes don't have garages, so shoveling out and clearing off the cars can take a long time.

What I don't quite get is the lifting of the windshield wipers. It seems to make it harder to clean the windshields. We never did that up north.

Posted by: celestun100 | January 29, 2010 4:36 PM | Report abuse

Celeste, I'm with you on the wiper's thing. I always chuckle when I pass cars like that in the parking lot. The only thing I can figure is maybe for icing/freezing rain?

Posted by: Brian-CapitalWeatherGang | January 29, 2010 4:41 PM | Report abuse

One word - Woohoo!

Posted by: ThinkGreen | January 29, 2010 4:41 PM | Report abuse

Tough decision! My husband is trying to decide whether to go to the Hampton area to plow, or stay local. Trying to make a call in the next 2 hours... Thoughts on if he should stay local (has govt. facilities to plow here..)

Posted by: plowerswife | January 29, 2010 4:42 PM | Report abuse

rginsburg: The Weather Service has time to issue advisories/warnings further to the North because the snow would start later in those locations. If the guidance continues showing 2-4 in or trends towards more in the metro area you should see an advisory issued later on today. From their afternoon discussion: THE SNOWFALL GRADIENT

Posted by: Andrew-CapitalWeatherGang | January 29, 2010 4:42 PM | Report abuse

Can someone send the Bastardi link where his is calling for 4-8 inches.

Posted by: FHDC | January 29, 2010 4:46 PM | Report abuse

Thanks rginsburg and then Andrew at CWG for the follow-up. I am now offically - barely, but officially - inside the 4-8" band according to CWG's latest map, but no advisories out.

Tracking this storm with y'all is waaay more fun than work :-)

Posted by: teezee210 | January 29, 2010 4:51 PM | Report abuse

GFS seems to have no change since the last model run -- still 2-4 in the DC metro area! Lets hope for a bit more of a push, but happy we look like we are going to get something!

Posted by: snowlover | January 29, 2010 4:54 PM | Report abuse

When is the next set of models runs set to come out?

Posted by: FHDC | January 29, 2010 4:54 PM | Report abuse

For anyone who understands what this means, 18z gfs is nearly identical to 12z gfs in terms of D.C. area accumulations. i.e., no shift to the north or south this time. If you don't understand this, don't worry. You don't have to be a weather model junkie to participate here :).

Posted by: Dan-CapitalWeatherGang | January 29, 2010 4:55 PM | Report abuse

FHDC, the 0z runs come out between about 9pm and 1am. NAM starts just before 9, GFS just before 11.

Posted by: Ian-CapitalWeatherGang | January 29, 2010 4:56 PM | Report abuse

The accuweather guys should really talk to each other. This is their 4:05 update and it keeps the snow south.

Posted by: formerwxman1 | January 29, 2010 4:58 PM | Report abuse

Bastardi 4-8 inch discussion is on the Accuweather Premium (pay) site.

Posted by: bbv91258 | January 29, 2010 4:58 PM | Report abuse

About lifting the windshield wipers: It is mostly for ice storms and sleet, but around here, we get our fair share of that. Having wipers up prior to a storm prevents them from freezing hard to the windshield, and possibly being damaged with an ice scraper. I actually damaged a wiper blade that way once; mangled the edge in just one small spot, but that was just enough to cause an annoying problem.

Melting the ice with heat from the car's running engine can take a long time, depending on how much ice there is. It also allows condensation to build up inside the car's motor as it just sits there running, causing damage which shortens the engine's say nothing of the environmental damage caused by running the engine the extra time needed to melt the ice or sleet buildup. It's always better to boost the melting process with ice scraping.

Everything you ever wanted to know about the lifting of wiper blades in anticipation of whatever frozen precip we may get!

Posted by: --sg | January 29, 2010 5:02 PM | Report abuse

Thoughts on Bastardi's 4-8 inch prediction? Not very familiar with him bc he is on pay side of accuweather. Does he hype as much as Margusity. That being said I do enjoy Henry's banter.

Posted by: FHDC | January 29, 2010 5:04 PM | Report abuse

Regarding the comments about the windshield wipers being lifted...I was in Toronto a couple of years ago around this time and I noticed that most of the cars in the parking lot of the client I was working for had their windshield wipers lifted.


Posted by: itstim | January 29, 2010 5:19 PM | Report abuse

With regard to Accuweather hyping, pretty much any weather site will get more traffic when something's up. Accuweather always seems a bit dramatic to me (the sky is falling, etc.). Who knows what kind of pressure CWG gets from the 7th floor, but I've never seen CWG stoop to the level of exaggerating the likely effect of a storm.

Posted by: fleeciewool | January 29, 2010 5:31 PM | Report abuse

Windshield wipers:

I guess in Michigan most people had garages and were more likely to get snow than ice.
Thanks for the info, I have lifted mine now:)

Posted by: celestun100 | January 29, 2010 5:38 PM | Report abuse

Correct me if I am wrong, but it looks like the 18Z NAM has shifted the precip northward somewhat. It has the northern edge of the 0.5 - 0.75 inch QPF now going through southern Fairfax County (it was north of Richmond on the 12Z run). Depending on the QPF/snow ratio, that's the potential for 5 - 10 inches!

Posted by: bdeco | January 29, 2010 5:42 PM | Report abuse

Latest update from southern Prince William: it's cold. DARN cold. ;-) You can be assured it will snow like gangbusters tomorrow, as I have a 10am appointment in Falls Church with my dermatologist. Hubby said, "honey, I'll drive so I won't worry about you". How sweet. I wanted to cancel, but he talked me out of it.

Bottom line: I'm packin' a blanket, some water bottles, and a couple of sandwiches for the ride, just in case. Something tells me it could be a LOOONG day in the car!

Posted by: southbridgemom | January 29, 2010 5:45 PM | Report abuse

Noaa still has 1/2 inch total and only a 40% chance of that for the (far) Northern suburbs.

Can't we get it to veer north again?:)

Posted by: celestun100 | January 29, 2010 5:48 PM | Report abuse

Just about to head for my dance...The weather today reminds me of that which preceded the big 1979 storm...there's some hope since they weren't predicting a major accumulation for the Metro area the day before that storm.

Posted by: Bombo47jea | January 29, 2010 5:51 PM | Report abuse

Thanks for the hope, the snowlovers in the Northern suburbs need it. I am telling my son and daughter to do the snow dance now.
Let it snow...

Posted by: celestun100 | January 29, 2010 5:56 PM | Report abuse

NOAA issues a winter weather advisory for DC and what was previous the advisory is upgraded to a warning...

Posted by: justhavingfun4u1 | January 29, 2010 6:10 PM | Report abuse

More on the wipers. Out here in Winchester when we got the big pre-Christmas snow it was nice to not have to dig through a foot of snow on the windshield to find them Sunday morning...

Posted by: ValleyCaps | January 29, 2010 6:19 PM | Report abuse

Wooo... Winter Weather Advisory for DC! The trend is our friend....

Posted by: SkywalkerSS | January 29, 2010 6:20 PM | Report abuse

Noaa raised our Saturday chances of 1 inch from 40%to 80%. Maybe I should have the kids do the snow dance again.

Posted by: celestun100 | January 29, 2010 6:22 PM | Report abuse

2-4, maybe more? Too bad CWG doesn't have a "much will it snow at DCA?" contest. Could boost page traffic to even higher levels!

Posted by: JerryFloyd1 | January 29, 2010 6:30 PM | Report abuse

Winter Storm Warning for Charles County...

Posted by: fleeciewool | January 29, 2010 7:03 PM | Report abuse

i'm really hoping for a shift and some snow in the baltimore area! come on shift!

Posted by: bachaney | January 29, 2010 7:42 PM | Report abuse

Still looks like a non-event looking at the current radar...just can't buy into these models.

Posted by: parksndc | January 29, 2010 8:30 PM | Report abuse

@parksndc, the storm is moving slightly north, and models are very accurate from less than 36 hours out

Posted by: samdman95 | January 29, 2010 8:52 PM | Report abuse

When can we look forward to the next official update? I'm wearing out the Refresh button.

Posted by: curlygirl2 | January 29, 2010 9:07 PM | Report abuse

Posted by: deveinmadisonva | January 29, 2010 9:08 PM | Report abuse

No advisory for MoCo? What gives? We're only a few miles north of DC...

Posted by: lilymama | January 29, 2010 9:16 PM | Report abuse

we have escaped! The forecast for fll

Partly sunny with a 20 percent chance of showers. Breezy. Near record highs in the mid 80s. South winds 10 to 15 mph becoming southwest around 20 mph in the afternoon.

Posted by: pvogel88 | January 29, 2010 9:18 PM | Report abuse

Hey CWG-- What do you all think the chances are the Winter Storm Warning will be extended to include Prince William? Just curious... Thanks!!

Posted by: southbridgemom | January 29, 2010 9:18 PM | Report abuse

what are thoughts on the 0z NAM? Has it lost its mind?

Posted by: mciaram1 | January 29, 2010 9:26 PM | Report abuse

Southbridge: Not CWG, but I'll answer. It'll be hard for them not to with the .6 QPF on the latest NAM. That'll mean about 8" of snow if it verifies.

Posted by: jpl1019 | January 29, 2010 9:27 PM | Report abuse

00Z NAM gives everything south of DC proper 5-10 inches.

Posted by: bdeco | January 29, 2010 9:29 PM | Report abuse

Sometimes the NAM overforecasts precipitation but it seems like a continuation of the trend with precip (up). It has some support from it's 'cousin' SREF which may be more reliable in this range and brings .5" liquid pretty close to the city.

Posted by: Ian-CapitalWeatherGang | January 29, 2010 9:34 PM | Report abuse

@jpl1019: Hey, I'll take the answer -- thanks!

Posted by: southbridgemom | January 29, 2010 9:37 PM | Report abuse

due to the cold, would .5 inches of liquid be more like 8 inches of snow?

Posted by: samdman95 | January 29, 2010 9:38 PM | Report abuse

As I said 48 hours ago: DC 1 -4 inches, more to the south.

Posted by: AugustaJim | January 29, 2010 9:44 PM | Report abuse

Things are really starting to get interesting here.
Any change in the initial start time with the snow? Are we still looking at late morning/lunch time?

Posted by: bodyiq | January 29, 2010 9:45 PM | Report abuse

"Thoughts on Bastardi's 4-8 inch prediction? Not very familiar with him bc he is on pay side of accuweather. Does he hype as much as Margusity"

Joe B has correctly predicted 37 of our last 2 major storms

Posted by: tgt111 | January 29, 2010 9:45 PM | Report abuse

samdman95, I think 15:1 ratios would be a decent and possibly conservative starting point. In this type of situation we could end up higher as well, so yeah.. that's fairly close (.5 would be 7.5 at 15:1). The NAM was as high as just about anything has been, since this initially jumped south, for DCA with .46".

Posted by: Ian-CapitalWeatherGang | January 29, 2010 9:47 PM | Report abuse

my prediction for D.C. 1-10 inches, points south 2-20 inches, points north 0-6 inches. I have 99% confidence in this prediction.

Posted by: samdman95 | January 29, 2010 9:48 PM | Report abuse

Yes and to give (weenie) props to the NAM, it is a shortterm model so this is its time to shine. Wait an hour to see what the other major american model (GFS) says.

Posted by: jpl1019 | January 29, 2010 9:56 PM | Report abuse

Blue Ridge Obs:

Low last night here was 9.5F. Hi today 22.3F. Currently 14.2 with a wolf moon overhead. Smells like snow.

Still no NWS advisory for Warren Co, VA...

Posted by: spgass1 | January 29, 2010 10:46 PM | Report abuse

New models pretty interesting, but radar is not too promising. Notice the virga hole around Sterling radar? That's going to waste a lot of snow on the way down to saturation.

Just because it is going to be so fluffy, I'm going to give 3-5 for DCA. North side of the District will be on the low side of this, F-Burg higher. Someone down south is going to get double digits.

Pat Michaels

Posted by: pmichaels1 | January 29, 2010 10:55 PM | Report abuse

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