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Posted at 11:05 PM ET, 02/20/2011

Monday night: Rain, sleet, then some snow

By Wes Junker, Jason Samenow and Dan Stillman

Some accumulation possible

11:05 p.m. Update: There's been a bit of sleet and snow mixed in with tonight's scattered rain showers, but don't worry about anything accumulating. Looking ahead, however, this evening's model information indicates an increasing chance of snow accumulation late Monday night into early Tuesday morning, which could slow the Tuesday morning back-to-work commute. Precipitation starts as light rain late Monday afternoon or evening, and then probably changes to sleet late in the evening before changing to snow (change-overs occur from north to south).

The most likely accumulations are now a touch higher than the range discussed earlier - around 1-2" inside the Beltway and to the east, south and southeast, with around 2-4" possible north, west, and northwest of the Beltway, and potentially 4"+ north and west of Baltimore (and all could be on top of a layer of sleet). Earlier we mentioned accumulations inside the Beltway and to the east, south and southeast as primarily on grassy areas. That may still be the case, but with the latest model data trending cooler for tomorrow's highs (50s instead of what once looked like 60s) and faster with the arrival of cold air tomorrow night, road accumulation can't be ruled out.

Overall forecast confidence remains on the low side given the complex weather pattern and the tricky task of estimating how much precipitation will fall once it gets cold enough for snow, and how much of the snow will fall heavy enough to stick to a ground which is warmer than it's been for most of this winter.

We'll be back tomorrow with full coverage, including an accumulation map, forecast details by zone, and SchoolCast.

PS: As far as tomorrow's holiday is concerned, it'll be mostly cloudy and there may be a few scattered showers around. But there should be plenty of dry periods, with highs in the 50s, until the late afternoon into evening brings an increasing chance of light rain.

Keep reading for our earlier update...

From this afternoon: Tomorrow temperatures are expected to rise to the mid-50s to low 60s and by tomorrow night as a cold front presses southward, we should get some rain. The big uncertainties revolve around how much precipitation will fall, whether and when the rain will change to snow and if any of the snow will stick.

Next accumulating snow chance: Monday night into early Tuesday
Probability of more than 1" of snow: 50%
Probability of more than 4": 10%

The models have gone back and forth about the timing of any changeover from rain to snow and on the exact location of the stripe of heavier precipitation. The event still looks like it will be more rain than snow with the potential for a period of snow toward the second half of the event late Monday night and early Tuesday morning.

There is potential for slick travel early Tuesday morning as temperatures steadily fall below freezing (as cold as the low-to-mid 20s according to one model). However, the warm daytime temperatures over the past week and on Monday should result in warm ground temperatures which may limit accumulations.

At this point, we generally think an inch or less of snow is most likely primarily on grassy areas from inside the beltway and to the east, south and southeast. North, west, and northwest of the beltway, 1-3" of snow is most likely. But as there are significant differences between the models on the timing of the rain/snow changeover and the amount of precipitation that will fall, so amounts could easily be less or more.

Tomorrow we will post an accumulation map and forecast details by zone.

Keep reading for technical discussion...

TECHNICAL DISCUSSION

The NAM and SREF guidance this morning has trended northward with its band of precipitation. Both sets of guidance are forecasting a tight precipitation gradient (the differences in precipitation amounts vary significantly as you shift across the band from south to north). The GFS from this morning brings in the cold air quicker than this morning's NAM and gives DC around 0.10 to 0.12" as snow but with the warm initial ground temperatures its forecast is hardly a ringing endorsement for accumulating snow. On the other hand, the latest European model would suggest upwards of 0.25" as snow - leaving open the possibility of several inches, especially north and northwest of the District.

nam-evolve-022211.jpg
NAM 24 hr accumulated precipitation ending at 7AM Tuesday morning from the last three model runs with the oldest run on the left and the newest on the right.

The figure above shows the 24 hour precipitation forecasts ending at 7AM Tuesday morning from the last three runs of the NAM with the most recent on the right and the oldest run on the left. The band of heavier precipitation was farthest south on the earliest run (far left) as it had the front and cold air penetrating the farthest south of any run. The latest run (far right) keeps the bulk of the precipitation to our north and doesn't really bring the cold air into the area until the precipitation has pretty much exited the region. The image with the precipitation farthest south had DCA in most snow of the three runs. The middle image had BWI in it while the latest had heavy snow north of the Pennsylvania border. The rate at which the band has shifted from run to run does not inspire confidence that subsequent runs might not shift the axis back south.

3:20 p.m. update: The latest NAM (18z) has come in a little colder and wetter and would support 1" around D.C. and 1-3" in the north and west suburbs. As the trend toward warmer air and less precipitation has now reversed, we'll need to keep a close eye on subsequent runs.

sref-022211.jpg

The SREF guidance (shown above) which had most members shift its precipitation axis northward like the NAM also argues that most of the precipitation will be over by the time the temperatures are cold enough to snow. SREF ensemble members provide information on the uncertainty of a forecast. The more variation in the members, the less certain the forecast. The plume diagrams below show the precipitation type that the various ensemble members are forecasting at during the storm and indicating when the precipitation is falling heavily (the steep slope), the accumulated precipitation (if all the precipitation were melted) and the temperature at 850 mb (5000 ft). Only one member forecasts as much as three inches of snow. Most forecast little or no snow.

The members do show significant differences in the amounts of precipitation that the storm might bring but are pretty unanimous that much of the precipitation will fall as rain at least for the DC area and to the south and east.

SREF ensemble plume diagrams are available for various locations here.

baltimore-sref.jpg

SREF output for Baltimore (shown above) is quite a bit more bullish than for DCA emphasizing that there is more potential for accumulation as you move north. Still, the mean snow forecast for Baltimore is only 0.24" (around 2" to 2.5" inches of snow assuming it all sticks, a bold assumption).

Perfect timing between the cold air, the surface wave, and the precipitation is needed in order for snow lovers to get their fix. Right now that seems less likely than a scenario featuring mostly rain with a little snow at the finish unless the axis of precipitation shifts back south on subsequent runs or the latest Euro model run is right.

Our forecast - summarized at the beginning of this post - is a blend of the various guidance - slightly biased toward the less snowy solutions because of the warm temperatures expected Monday (and the fact that rain to snow scenarios often underperform with respect to snow amounts). But this is a very close call and the forecast may need to be tweaked to allow for more or less snow.

By Wes Junker, Jason Samenow and Dan Stillman  | February 20, 2011; 11:05 PM ET
Categories:  Latest, Winter Storms  
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Next: Forecast: Sleet & snow tonight, temps to plunge

Comments

Anything to saturate all the dry brush and ground to prevent another crazy day like Saturday is OK with me. It was like we were living in Southern California in August on Saturday. Fires kept breaking out left and right and there were scenes of people standing in their suburban backyards with hoses trying to save their houses.

Posted by: rwalker66 | February 20, 2011 3:38 PM | Report abuse

I think there is something wrong with the NWS at a glance
The last day of the weekly forcast says a high of 59 but a chance for rain and snow
WTF??

Posted by: redskins-95 | February 20, 2011 3:39 PM | Report abuse

@redskins-95

We're doing some maintenance on the at a glance forecast. Hopefully will be finished soon.

Posted by: Jason-CapitalWeatherGang | February 20, 2011 3:46 PM | Report abuse

@rwalker : where do you live ?? i'm sorry to hear about the fires near you -- i've not seen anything like that here in Alexandria ...

Posted by: neko-chan | February 20, 2011 3:53 PM | Report abuse

I live in the Fair Oaks area where there was a big brush fire. The scenes of people standing in their backyards with hoses I saw on the news. I think those scenes were from Maryland. I just walked over and took a lot of pictures of the fire damage near me. Anyone know where I can post them for CWG readers to see and still maintain my privacy? I put them on my Facebook and Photobucket accounts, but I don't want to put links to those.

Posted by: rwalker66 | February 20, 2011 4:12 PM | Report abuse

no models will verify this thing until prolly sometime tomorrow as the 1st low is overhead. will prolly end up being a nowcast with radar. I still dont think the cold enough for snow air is gonna come in until after low 2 moves by us here in DC. Looking like a snow event north of DC, i think 1 inch accumulation is still far fetched with this much uncertainty in the models.

Warm air will be here tomorrow thats a given, timing of when it moves out is not a given. And even if the models say it is, it rarely happens that way when daytime temps are in the 60s.

If daytime temps were low to mid 40s, maybe, but 60s... I call BS.

Posted by: KRUZ | February 20, 2011 4:18 PM | Report abuse

i like the trend of the 18z NAM: colder & wetter!

wes, jason, CWG,
yesterday, wes mentioned the euro being the "lone holdout". today wes just mentioned how we could get more snow if "the latest Euro model run is right." well...WHAT'S THE LATEST EURO SHOWING?!?!** the day before yesterday ian pointed out the euro's better "verification" statistics. why does wes seem to favor/focus on the gfs/nam over the euro?

**if the proprietary nature of the euro precip data prevents you from saying what it is, then can i take guesses at snow amounts, and have you nod or shake your heads?

Posted by: walter-in-fallschurch | February 20, 2011 4:19 PM | Report abuse

For what little its worth, TWC (broadcast, not website) shows the DC metro being in the heart of the snow swath Tues morning into Tues afternoon.

Posted by: TBAlexandria | February 20, 2011 4:21 PM | Report abuse

Usually I root for snow, but thus time I'll take anything. The darn snow hole has made it so dry. The mulch fire near 198 was pretty scary and I just want more moisture.

Posted by: biketraveller22 | February 20, 2011 4:36 PM | Report abuse

Snow is Nature's instrument for eliminating incompetent motorists from the gene pool.

Posted by: localgoober | February 20, 2011 4:42 PM | Report abuse

Pics of the aftermath of a big brush fire in my Fair Oaks neighborhood:

http://www.flickr.com/photos/52129862@N06/sets/72157625971561787/

Posted by: rwalker66 | February 20, 2011 4:42 PM | Report abuse

i wonder when we'll get our first individucast (h/t firedragon) request? i.e., "i have an appt at 10:00 on tuesday in fairfax etc..."

Posted by: walter-in-fallschurch | February 20, 2011 4:44 PM | Report abuse

I'll take any precip at this point. If it has to be the frozen variety, I can live with that. The brush fires everywhere are alarming.

Two of my acres are field, right below my house. I re-attached the garden hose to the outside spigot a few days ago, and have the nozzle ready for immediate attachment if necessary.

Posted by: tinkerbelle | February 20, 2011 5:00 PM | Report abuse

18Z GFS seems to move the storm a bit faster than the NAM at 36 hour mark.

540 line still north of DC during heaviest precip. With the way ppl are getting excited in here for this, a possible 1 incher actually has bust potential!!!!

GFS
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/18/images/gfs_slp_036m.gif

NAM
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/18/images/nam_slp_036m.gif

Posted by: KRUZ | February 20, 2011 5:01 PM | Report abuse

About this time of the year in 1987, Sunday afternoon saw a high in the low 50s and that night 10" snow fell. I don't see DC getting anything close to that this time around on Monday night-Tues a.m. (and for once I hope we don't, because I too have an important "appointment" Tuesday afternoon). But mild daytime temperatures and nighttime snow are not unheard of around here.

In fact the Veteran's Day snow later in 1987 was preceded by several very mild days.

And in the late 1960s it was 85 degrees one March afternoon and the next morning there were snow flurries.

Posted by: JerryFloyd1 | February 20, 2011 5:08 PM | Report abuse

Walter, we mention in the blog. "On the other hand, the latest European model would suggest upwards of 0.25" as snow - leaving open the possibility of several inches, especially north and northwest of the District."

Posted by: wjunker | February 20, 2011 5:24 PM | Report abuse

wes,
oops...thanks. somehow i missed that sentence. so why do you seem to favor, or at least focus on, the gfs and nam solutions over the euro?

jason,
a while ago CWG did a post about the 6 or 7 year cycle for big snows in dc. i can't seem to find that in the archives. can you?

Posted by: walter-in-fallschurch | February 20, 2011 5:32 PM | Report abuse

Just saw Chicagke Windler on ABC evening news reporting on the blizzard in Minnesota. I remember her rather brief OCM stau at WRC; glad to see she's thriving in Minnesota.

Posted by: JerryFloyd1 | February 20, 2011 6:17 PM | Report abuse

LMAO....

BigJoeBastardi: "You gotta admit lovers of WILD WEATHER, this pattern is what you love! Should have 3-6 NYC front runner, DC gets the 3-6 #2"

Posted by: KRUZ | February 20, 2011 6:20 PM | Report abuse

Chikage is correct spelling of Ms. Windler's first name. Not everyone is from Chicago Land.

Posted by: JerryFloyd1 | February 20, 2011 6:21 PM | Report abuse

If Bastardi is saying 3-6" that means, we get minus 4.5" inches and our YTD snow total drops to 5".

Posted by: JerryFloyd1 | February 20, 2011 6:27 PM | Report abuse

Lots of rain showers popping up out there. Drove through numerous moderate to briefly heavy showers coming from Fredericksburg to Centreville VA.
Obnoxious to drive in, but moisture is GOOD.
More tomorrow.....yay!

Posted by: FIREDRAGON47 | February 20, 2011 7:09 PM | Report abuse

We just had a moderate snow shower in Oakton, VA that lasted a few minutes. It is 41 degrees so everything melted instantly.

Posted by: Kevin-CapitalWeatherGang | February 20, 2011 7:29 PM | Report abuse

Not to quibble with the forecast of rain - but it looks and sounds like sleet mixing in right now inside the beltway to me.

Posted by: manatt | February 20, 2011 8:00 PM | Report abuse

CWG --

The comments section looks strange to me (using latest version of Firefox); no separation between the comments. Is anyone else seeing this?

And it's good to see JerryFloyd1 commenting again :-)

Posted by: natsncats | February 20, 2011 8:09 PM | Report abuse

Natsncats
Same here! I'm also using Firefox.

BTW, the CWG should publish a weather calendar (complete with Keith's pictures and weather records). Jason Samenow would be Mr. January, and so on. Quotes (or nifty one-liners from repeat commenters) could be included. The proceeds could be donated if it comes to that.

How awesome would that be!!

Posted by: JSTF | February 20, 2011 8:26 PM | Report abuse

natsncats--I noticed the same thing. This comment section is messed up, but previous ones today looked fine.

Posted by: petworthlad | February 20, 2011 8:26 PM | Report abuse

yeah same problem with the comments section here too. Im using Safari.

Posted by: KRUZ | February 20, 2011 8:33 PM | Report abuse

Yeah, comments look weird to me too (Chrome)

Rained here in South Laurel, my husband said it was snowing in Columbia.

Posted by: megamuphen | February 20, 2011 8:40 PM | Report abuse

walter-in-fallschurch, I sometimes show the European model but the graphics I have access to our not as good as for the GFS or NAM. I also don't have the capability to look at european model soundings or at 3 hourly output like I do for the NAM . That's probably the reason I show the latter more often especially at these time ranges where I can look at the sounding to get a better feel for the actual changeover from rain to snow. The european model is really good model but with the sref, gfs and nam less bullish, I'm not yet willing to go with its more bullish forecast.

as to your question about the 7 year cycle. It was in one of my early season articles or in the comments about it but I tried to find it and couldn't.

Posted by: wjunker | February 20, 2011 9:12 PM | Report abuse

A bit of sleet here in the center of Warren county. I'm using Safari also which is new for me (just bought a MacBook on friday) Usually there's a different font for the posted by section.

Posted by: eric654 | February 20, 2011 9:13 PM | Report abuse

This is getting kinda interesting. Latest NAM would suggest at least 0.3" liquid QPF all snow at Reagan, with a temp of 24 degrees by 7 am Tuesday morning.

Posted by: Jason-CapitalWeatherGang | February 20, 2011 9:20 PM | Report abuse

Jason, I was just going to post that. The sounding for BWI has the changeover at 03Z so our readers up that direction would have more than that.

Posted by: wjunker | February 20, 2011 9:26 PM | Report abuse

Oops, 03Z is around 10 PM so sometime in the 10 to 11 PM range would be the nam changeover at BWI and around 12 or 1AM for DCA as it still has a warm layer temp of +0.2 at 1Am. That cold enough for snow. It also suggests sleet by 10PM for DCA.

Posted by: wjunker | February 20, 2011 9:29 PM | Report abuse

It looks like the cold air will lurk just to our north tomorrow (e.g. central PA) ready to swoop back down tomorrow night. Hopefully it will still be nice enough here (i.e. dry and mild) to change the oil.

Posted by: eric654 | February 20, 2011 9:47 PM | Report abuse

Centreville Va Brief hard rain shower. Love it.
Hope the rain ends before we go to Mt Vernon tomorrow morning.
Comments section looks funny tonight.

Posted by: FIREDRAGON47 | February 20, 2011 9:53 PM | Report abuse

Jason --- would most of the precip already be over by 7AM on Tuesday? It would be nice to get a good chunk of that snow falling with temps in at least the mid-to-upper 20s --- i assume that would increase the likelihood of sticking, no?

Posted by: jms12 | February 20, 2011 9:54 PM | Report abuse

Also, Jason (or Wes). Is the latest NAM different enough to warrant an updated forecast, or is it in line with the broad parameters of your earlier guidance?

Posted by: jms12 | February 20, 2011 9:56 PM | Report abuse

0.3" liquid QPF all snow at Reagan...

So exactly how much snow would that be?

Posted by: KRUZ | February 20, 2011 10:03 PM | Report abuse

thanks wes,
hearing/seeing euro top-secret precip info feels like reading the teacher's manual or something.... i guess you are (were?) reluctant to go that way 'cause it was the outlier.

3"...i'll take it! this is an entirely different animal than what the nam showed earlier. heck, it's better than what the euro had earlier. this improvement is because of an earlier changeover, right? if so, what's bringing in the cold air earlier?

i bet KRUZ is shakin' in his snow boots.

Posted by: walter-in-fallschurch | February 20, 2011 10:05 PM | Report abuse

walter

lol i drive in the snow, not walk in it ;) dont need any snow boots.

either way, as ive said before, ill believe the accumulating snow when i see it!

models have done this before this very winter and come go (snow) time things dont work out as planned. ill be ready either way, but i wont be disappointed when theres no accumulating snow to be found!

Posted by: KRUZ | February 20, 2011 10:12 PM | Report abuse

OK, I read this blog alot and love the work you all do, CWG! What's the likelyhood of my flight scheduled to land at IAD Monday night at 9 PM to get cancelled? As much as I hate leaving 84 degrees here in Florida, it's time to come home. Thanks! :)

Posted by: kridgely | February 20, 2011 10:14 PM | Report abuse

@jms12

Close to all of the precip is done by 7 am Tues. We may tweak our forecast in a short update at the top of this post around 11 p.m.

Posted by: Jason-CapitalWeatherGang | February 20, 2011 10:17 PM | Report abuse

The 0z NAM shows a lot of qpf. Has the ceiling risen in terms of snow accumulation for this storm if temps are colder than expected or are we still looking at like 4" max?

Posted by: Dylan0513 | February 20, 2011 10:23 PM | Report abuse

well if we end up with 3 inches or more of snow then it looks like we can chalk up another win for FEARLESS JOEY as he was calling for 3-6 inches for dc/bmore since last monday.

Of course, when this busts, all mets will be laughed at!

Posted by: KRUZ | February 20, 2011 10:28 PM | Report abuse

Walter!! The 'individucast' term was my creation! No hard feelings; just want to set the record straight - I hope this thing turns around to bring us more snow, to get us out of near-drought mode, get the snow-removers some extra overtime cash, and get you some sculpture-ready snow! BTW if you noticed, the dreaded individucast request came in after all, just a little later than you expected ;) Great job CWG as always - you're the DC area's go-to crew when it comes to weather forecasting and reporting!

Posted by: kolya02 | February 20, 2011 10:43 PM | Report abuse

@kridgely

No need to worry about flights being canceled landing at 9 pm. I dont think it starts to deteriorate until after 10 pm, and even then, this isn't a crippling "cancel flight" kind of storm.

@Dylan0513

If everything came together perfectly for snow, could see some 4-8+" totals, but most likely n & w of baltimore the way it looks now. gotta watch this though.

Posted by: Jason-CapitalWeatherGang | February 20, 2011 10:45 PM | Report abuse

I figured I ran the risk of getting in trouble for asking. ;) I saw the timeline for the changeover for BWI and DCA but not IAD.

Posted by: kridgely | February 20, 2011 10:48 PM | Report abuse

And thanCWG Jason! Have a great night! :) Go CWG!

Posted by: kridgely | February 20, 2011 10:51 PM | Report abuse

0z GFS looks to be on board at least in terms of a lot of qpf, although less than the NAM.

Posted by: Dylan0513 | February 20, 2011 10:53 PM | Report abuse

Thanks, I mean!

Posted by: kridgely | February 20, 2011 10:56 PM | Report abuse

kolya02,
oh, man, i's so sorry...:-( you're right, dag nabbit! it was you're term - and is has been added to the CWG lexicon. not sure why i mixed you two up.... my bad. good term, though. and it didn't take long to see one requested.

it thrills me that this storm has risen to a level that it could generate an individucast request! i'm west of baltimore, so, jason just promised me 8" ;-)

Posted by: walter-in-fallschurch | February 20, 2011 11:00 PM | Report abuse

CWG:

Where would you like me to deliver the fresh schoolcast apples? I was hoping to deliver them to the top of the page. Would you like 2 or 3? :D

Posted by: ArlTeacherSnowman | February 20, 2011 11:04 PM | Report abuse

drat! "YOUR term", i mean.

Posted by: walter-in-fallschurch | February 20, 2011 11:05 PM | Report abuse

@ArlTeacherSnowman

No SchoolCast til tomorrow... But I like the chances for a snow day Tuesday based on tonight's model data.

Posted by: Jason-CapitalWeatherGang | February 20, 2011 11:09 PM | Report abuse

@CWG You're making my 3-day weekend!

Posted by: ArlTeacherSnowman | February 20, 2011 11:13 PM | Report abuse

If the trends holds on later model runs, northern tier of MD counties would need a winter storm watch TUE morning (a big if). That northern tier in MD and southern PA has more QPF and an earlier change over to snow TUE evening.

Posted by: ronbcust | February 20, 2011 11:21 PM | Report abuse

If the trends holds on later model runs, northern tier of MD counties would need a winter storm watch MON morning (a big if). That northern tier in MD and southern PA has more QPF and an earlier change over to snow MON evening.

Posted by: ronbcust | February 20, 2011 11:22 PM | Report abuse

The 1-2 inches of slush snow will freeze over for the Tuesday am commute. It's going to be a mess. Most schools will most likely close.

Posted by: SNOWLUVER | February 20, 2011 11:26 PM | Report abuse

no problem, Walter....Thanks for the credit, and really I only brought it up to regain some credibility here after starting some awful snow lover/hater debates earlier this winter :o . In wishing for snow we're probably just clinging to any straws that didn't burn up on Saturday, but still, this is fun, isn't it??

Oh and ArlTeacherSnowman excellent line! I pictured the schoolchildren lined up with shiny red apples to deliver to Wes, Jason, and the rest of the Gang.

Posted by: kolya02 | February 20, 2011 11:32 PM | Report abuse

Nice to see this board light up tonight.

Posted by: petworthlad | February 21, 2011 12:56 AM | Report abuse

Snow, please! Fluffy white flakes falling are like fairy dust...

Posted by: SusanMarie2 | February 21, 2011 5:37 AM | Report abuse

Same problem with the comments sections. (chrome)

Laytonsville: No real precip to report. Deck looks like something really light may have fallen overnight, but not enough to moisten more than a few spots.

NWS saying 1-3" IMBY overnight. Hard to believe after last week.

Posted by: dprats21 | February 21, 2011 6:33 AM | Report abuse

The comments to this entry are closed.

 
 
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