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

Questions linger for Tues/Wed snow potential

By Jason Samenow

Some accumulating snow likely, but amounts may vary

* Sunny start and end to week: CWG's Full Forecast *
* Winter Storm Watch Tues.-Wed. for most of metro area (map) *

Next Chance of Accumulating Snow: Tuesday P.M.-Wednesday
Probability of Accumulating Snow (1" or more): 85%

A complex storm system developing in the center part of the country today likely spells some trouble for our region as Tuesday progresses. An area of low pressure in the Deep South looks to join forces with an energetic disturbance diving south along the Polar jet stream Tuesday night.

Light snow, possibly mixed with sleet, will break out across the region between mid-day Tuesday and Tuesday evening as moisture ahead of the southern low streams northward. As the northern stream disturbance interacts with the southern low off the mid-Atlantic coast, an area of heavier snow is likely to develop overnight. The exact location of this interaction will help determine exactly how much of the area gets the heavy snow.

At the moment, it appears the best chance of any heavy snow will be from the District and to the northeast. Areas to the south and southwest may get "dry slotted" as the energy from the northern disturbance shifts to off the coast. In other words, places like Baltimore and Philadelphia have a better chance of getting heavy snow than the D.C. metro area and especially our southern suburbs.

Keep reading for additional discussion of the Tues-Wed snow potential

If the northern stream disturbance is able to dig a little further south than indicated by the models, heavier snow would impact a larger region (extending into the southern suburbs) and for a longer period of time, lasting perhaps through Wednesday morning.

But if the northern stream disturbance tracks to our north, the National Weather Service correctly notes the following:


The bottom line is that current models put the District on the boundary between moderate snow and heavy snow, and the southern suburbs on the boundary of moderate snow and light snow.

Our current best bet is that the District and points north and east will receive moderate snow amounts, with lighter snows to the south and west. But other possibilities remain on the table. Here's our current assessment of possibilities:

Less than 1" of snow: 15%
1-4": 25%
4-8": 40%
8"+: 20%

Most likely: 3-6" for immediate metro area, more north and east, less south and west

The Snow Lover's Crystal Ball appears when the potential exists for accumulating snow beyond 24 to 36 hours.

By Jason Samenow  | February 8, 2010; 5:00 AM ET
Categories:  Snow Lover's Crystal Ball  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Update: Significant snow likely Tues.-Wed.
Next: Forecast: Remarkable winter brings new threat


That 15% will grow to 100% as the storm draws near, yes?

Posted by: Murre | February 8, 2010 5:47 AM | Report abuse

I want as much snow as this system can place upon us, although I have to admit that I would prefer a drier variety if the amounts are over 8", because power outrages aren't all the rage (We already have a broken washing machine in my household, which died the very first night of this storm, and I'll have to clear a path around the entire house if we even manage to get a new one delivered). Hand washing is annoying, but at least I have power, so I'm not going to gripe too much (I'm having a blast in the snow anyways :-)

Posted by: TheAnalyst | February 8, 2010 7:38 AM | Report abuse

We have a broken washing machine too. Have no idea how/when we'll get a new one delivered as well. Not happy about putting out the bucks, but on the bright side, we kept power the entire storm and everyone is healthy and just a *little* bit of cabin fever setting in.

Posted by: sfurin | February 8, 2010 8:17 AM | Report abuse

Murre, you need to go back to elementary school as apparently they didn't teach you how to read or how to do math very well.

Posted by: Thundershock | February 8, 2010 8:52 AM | Report abuse


This system (aloft) is eerily similar to the Feb 5 1978 event, just after its 32 year anniversary. For that one, I remember a sharp SW to NE gradient; even the central eastern shore was above a foot. Philly and NY got 12-18 inches, and Boston was buried.

There were some notable surface differences; for one, the airmass leading and following the event was much colder. I think the DC area fell into the teens for highs after the storm developed along the coast.

The bad news? Model trends continue to shift a teeny bit south with each run. Unlike 1978, there is a more vigorous subtropical jet to tap. That means locations north and northeast of DC that had nearly a yard of snow last weekend could see up to a foot more. And, thundersnow is not out of the question in those areas, given the intensity of the upper system.

Where the low level convergence sets up - even for only a couple of hours - brief snowfall rates may reach 2 to 3 inches per hour, dropping a quick six. Will be interesting to watch this from afar Tuesday evening/overnight...

Bottom line: that "crystal ball" looks on the mark for DC metro, but could wildly increase to the north and northeast. Already, the NWS in Philly is not ruling out 2 MORE feet for areas that received 2 feet on Saturday. Yikes!

Posted by: wxdancer | February 8, 2010 9:00 AM | Report abuse

Thundershock, that's my wishcast. Less than 1 inch of snow (and none as rain).

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

I agree with the NWS position on the storm - we rarely get anything heavy off of the continent, whether it's rain or snow. A dusting to a couple inches maybe; but we absolutely need coastal development if we're going to get buried again.

Posted by: fleeciewool | February 8, 2010 9:22 AM | Report abuse

I'm hoping for 8"+, maybe another 12" storm. If we get another 4-6 inches Fri-Sat, we'd have about 4 feet of snow on the ground.

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

The NAM, with the 12Z run, is starting to join the GFS, with a more southerly, juicier solution, that delivers 10+ inches to the DC area.

Posted by: bdeco | February 8, 2010 9:35 AM | Report abuse

Wow, look at what the 12z NAM did with the storm for us: 12-15"

The NAM had been the model that was saying only 5-7" for us up until now and the GFS was saying higher than that. Maybe they're both in agreement now?

Posted by: Dylan0513 | February 8, 2010 9:36 AM | Report abuse

In the phrases "12z NAM" and "18z NAM," what do the numbers mean? Time of day? Altitude?

Posted by: InVA1 | February 8, 2010 9:47 AM | Report abuse

I am a newb....I am also a SNOW LOVER!!! Have to say I was actually SAD the snow stopped on Saturday. I am however excited we are getting MORE...Well hopefully....I live further south in North Stafford just south of Quantico. we are NOT in the warned area as of yet...WILL WE BE?????? (fingers crossed)

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

The 'z' refers to Zulu time. These models are run every six hours, so you get a 0z, 6z, 12z, and 18z run.

Posted by: JoeThePhotographer | February 8, 2010 10:00 AM | Report abuse


They refer to the time the model was run in Zulu time/UTC/GMT. In other words, the 12z run happens at 7 am EST.

Posted by: noahmamis | February 8, 2010 10:05 AM | Report abuse

I'm fairly certain Z refers to Zulu time, aka Greenwich Mean Time.

Posted by: seraphina | February 8, 2010 10:07 AM | Report abuse

GFS through 36 hours (12z run) is maintaining trend. Get ready.

Posted by: wxdancer | February 8, 2010 10:45 AM | Report abuse

..and 12z GFS brings somewhere in the range of 12-17" to DC

Posted by: Dylan0513 | February 8, 2010 10:52 AM | Report abuse

The 12z GFS would be a very serious storm for this region. Though it won't have as a much moisture as Snowmageddon, it's a more intense cyclone that will be capable of producing some very high winds. This may be evolving into a dangerous situation.

Posted by: Jason-CapitalWeatherGang | February 8, 2010 11:05 AM | Report abuse

living now in SW Florida,we truly do not miss snow.Our back was already broken while living in Upstate NY. I feel sorry for the people who are being hit hard by one snow storm or the other.May be this experience will make them think differently.

By the way, what happened to GORES and alike who are working on Global warming and Green movement- even monkeys and birds understand.May be many of the Washingtonians as well as the new occupants need to read about Global cyclic changes.I hope this is lessen for many who have never experienced such large scale SNOW. Use public transportation and not a car, otherwise it will clogup the system

Posted by: jayrkay | February 8, 2010 11:08 AM | Report abuse

All: First time poster here and am enjoying your commentary. Trying to understand your determination of snowfall based on the 12z GFS data. When I BING it, I see a loop showing various colors of green and blue crossing over the US. Assuming the data on the left is inches of rain, are you all translating that to snow? Or am I looking at the wrong loop?

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


1. climate and weather are not the same.

2. global warming translates into more erratic events on either side of the spectrum, ie. going several winters with no snow and then experiencing one winter with an abnormal amount of snow, as opposed to having relatively normal amounts of snow on a fairly consistent basis.

3. based on experience, i can tell you that people on this site generally don't like it when posters try to politicize the weather.

4. since you clearly have a tenuous grasp on even the basic definition of "climate change," maybe you'll want to keep further posts confined to the weather itself, and not the politics surrounding it.

Posted by: spankyman111 | February 8, 2010 11:16 AM | Report abuse

Damn, my roof just started leaking. Climbed out on the lower roof and observed a small ice dam forming along the length of the upper roof, which is pooling the melting snow. I shoveled 2.5' off of the lower roof, the last thing we need is more of this or there will be alot of roof damage out there.

Posted by: jamserve | February 8, 2010 11:19 AM | Report abuse

We get another 12" and they need to declare this area a disaster area and send in federal money for the people that it is affecting. This crap is out of control with the constant rain and snow in this area for the past year. Enough is enough already! I swear in all my life I have never seen the like of the amount of precipitation that NoVa has received in the past year.

Posted by: j0nx | February 8, 2010 11:23 AM | Report abuse

bets on Fed Gov opening Tuesday or Wednesday? Additional snow will probably cripple Metro for the rest of the week, meaning I can't get to work downtown....

Posted by: bmp246 | February 8, 2010 11:30 AM | Report abuse

For the laymen among us:

NAM = North American Mesoscale, a short-term weather forecasting model
GFS = Global Forecast System

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

Hmmm - NBC4 just lowered their amounts for this storm to 3-5 inches with the far north and west getting 5-10 inches. This does not make sense with all of the latest guidance.

Posted by: stinkerflat1 | February 8, 2010 11:51 AM | Report abuse

I can't believe that WTOP is still saying 3-6 inches with no mention of the upside potential. It's like deja vu all over again...

Posted by: bdeco | February 8, 2010 11:51 AM | Report abuse

stinkerflat, bdeco:

I don't think they have any idea what they are talking about! Their level of incompetence is stunning sometimes. Both the NAM and GFS said more snow (and it was interesting to see both of them be so similar)

Posted by: snowedin85 | February 8, 2010 11:59 AM | Report abuse

Are the models now pointing to Baltimore being more towards the center of this next storm than Philadelphia? I think both of the last storms did as well in the Philly area as here even though we were supposed to be the bullseye.

Posted by: rocotten | February 8, 2010 12:02 PM | Report abuse

it could be that mets are afraid to tell us there's more significant snow on the way. or, could be that they themselves just can't believe it!

Posted by: walter-in-fallschurch | February 8, 2010 12:03 PM | Report abuse


Posted by: srodens | February 8, 2010 12:04 PM | Report abuse

Well, it's excitin' that's for sure. I just drove out of my neighborhood (subdivision) here in Manassas to go to the grocery store. Here's my traffic update: in this subdivision (and others I passed) most streets are plowed about 1 and 1/2 lanes wide (you have to pull over to let someone pass). The major streets of Manassas are fairly clear, but there are huge mounds of plowed snow at the intersections which diminish visibility considerably. Short take: you can get around but if you don't have to, don't.
Hope this is helpful.

Posted by: dschalton | February 8, 2010 2:58 PM | Report abuse

That's a lot of snow! Hope y'all stay warm!

Posted by: houston123 | February 9, 2010 7:05 PM | Report abuse

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