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Posted at 1:45 PM ET, 02/ 2/2011

Saturday storm trending wet not white

By Wes Junker

Computer models are now indicating that another storm will likely impact the area over the weekend, probably on Friday night and Saturday and probably with mainly rain.

The storm will have little cold air to work with so the track would need to thread the needle like it did during the Commutageddon event to produce snow. Right now that looks unlikely. The overall pattern is not very favorable for us getting a snowstorm this weekend.

Our next shot at winter weather will not arrive until at least the next Tuesday or Wednesday with the arrival of the next shot of cold air. The potential for any storminess around that time is a big question mark as the models differ significantly on whether a new storm will form along that incoming Arctic front.

Let's first look at the pattern for this weekend's storm and discuss why it is likely to be rain rather than snow, sleet or freezing rain. It's still too early to estimate how much precipitation it will bring.

Right now, Saturday looks more wet than frozen but the latest models do suggest that the storm could start as a brief period of mix to the north and west of the city before transitioning to rain. This does not look like a storm in which the models will trend colder as we approach the event as there is not expected to be much cold air around to tap. However, we'll be watching to make sure our initial assessment about precipitation is right and that Mother Nature doesn't toss us a surprise.

TECHNICAL DISCUSSION

The lack of cold air makes the track of the southern system paramount in determining what type of weather the system will bring to our area. For us to get wintry weather on a track similar to the recent thunder snowstorm. The southern jet stream 500mb (18,000 feet) trough (dip) needs to track south of the Washington area

Along this southern jet stream, the associated low pressure center also needs to stay relatively strong. For those who have forgotten: the track of the 500 mb center during the thundersnow event is shown below. Note that it tracked just to our south and how it remained a closed circulation as it passed our area. In response to this intense mid-level circulation, a surface low developed rapidly off the coast and the dynamics and strong vertical motions caused strong cooling as the heavy precipitation moved into the region (see below) despite there being not an Arctic surface high pressure system to our north or northwest to give us cold air.

020511-1.jpg
Evolution of mid-level (500mb or 18,000 ft) low pressure area during January 26, 2011 storm

By contrast, the models are forecasting the southern stream shortwave associated with the upcoming weekend storm to lift to out north and west. Part of the problem is that there is a strong upper ridge off the West Coast so any northern stream system is likely to amplify enough to hold the mean trough far enough west to pull the southern stream system northeast on a track west of us.

The last couple of GFS and NAM runs have locked into this general solution though they have differed somewhat in the exact evolution. This morning's GFS 500 mb forecast is shown for comparison with the thundersnow event.

020511-storm2.jpg
Evolution of mid-level (500mb or 18,000 ft) low pressure area predicted for February 5, 2011 storm.

Note above how much stronger the northern stream system is and how it captures the southern stream system that tracks from Tennessee almost directly over the District. During the thundersnow event, the upper low stayed consolidated and tracked to our south. The NAM model's track is even more northerly with the southern stream impulse relative to the GFS. To get a snowstorm, the track of the southern stream impulse needs to be around 150 miles to our south which is a far cry from the current track on any of the operational models.

wes-stormcomparison-0211.jpg
Comparison of temperatures and flow at 5,000 feet during January 26, 2011 storm and predicted (NAM model) February 5, 2011 storm.

More importantly, the GFS and NAM now develop a surface low inland over the Southeast rather than off the coast. Such an inland low position and track invariably causes our temperatures to warm up. Also, instead of having the 850 mb (5000 ft) cyclonic (low pressure) circulation pass just to our south, the strong northern stream initially keeps any circulation at 850 mb well to our northwest so the region ends up in a broad region of warm air advection (winds from the south) which leads to warming.

Note to the right the differences between the forecast 850 mb pattern (bottom panel) and the pattern during the snowstorm (top panel). During our snowstorm, the closed 850 mb circulation tracked across southern Virginia keeping the metro region on the cold side of the storm. During the upcoming event (the bottom panel), the flow across the mid-Atlantic region is from the south which should cause temperatures to warm ahead of the storm.

When will winter return?

Both the GFS and European models and the bulk of their ensemble members suggest that cold weather will return by next Tuesday with the European model bringing the front through as early as Monday evening. Behind the front temperatures are expected again to be colder than normal.

Some of the ensemble members and one of the GFS runs last night, developed a wave on the front that might threaten the area with snow. The European model would call for cold behind the front with any wave on the front occurring well out to sea. This morning's GFS kept any wave development too far out to sea to impact us. However, there is not much skill in predicting where a wave might develop at those time ranges. NOAA's Climate Prediction Center 6-10 day outlook for that time range is predicting colder than normal temperatures and with above normal precipitation suggesting the period is one to watch closely.

Summary

A rain storm looks like a good bet for Saturday. It is too early to try to pinpoint exactly how much. A number of SREF ensemble members and this morning's NAM suggest the precipitation will be on the light side. The GFS and Euro predict over 0.50" from the storm. North and west of the city, the precipitation could start as a mix if the GFS is correct and the Euro might suggest a little snow on the backside. Any frozen precipitation west of the city looks like it would be short lived before changing to rain. The good news for winter weather lovers is that another shot of cold air looks like it will arrive for a couple of days starting around Tuesday.

By Wes Junker  | February 2, 2011; 1:45 PM ET
Categories:  Latest, Winter Storms  
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Next: PM Update: Brief warmth quickly turns colder

Comments

Good. Wash that snow and ice away. I'm a pedestrian and a lot of sidewalks are still covered in ice and snow and very treacherous to walk on.

Posted by: rwalker66 | February 2, 2011 2:05 PM | Report abuse

rwalker

Agreed, Rain is a welcomed site for me!

Hopefully if tuesdays storm is snow it will be followed by an early start to spring shortly after! Cant wait for Bastardi's predicted 70 degrees by the end of february!

Posted by: KRUZ | February 2, 2011 2:09 PM | Report abuse

Sounds as though Bastardi as well as a couple of other folks are thinking that a somewhat extended warm-up is coming mid-February.

The low confidence AccuWx 15-day forecast seems to indicate that as well with temps Valentine's weekend at or above normal.

Posted by: ThinkSpring | February 2, 2011 2:22 PM | Report abuse

Wes,

I agree with your forecast. With La Nina and no blocking, it's hard to get very excited about snow at this point.

The ironic thing about the next system is that it might cause snow in south Texas while we end up getting rain.

Posted by: frontieradjust | February 2, 2011 2:31 PM | Report abuse

rwalker, Tuesday is just the 1st cold day, any wave would probably be wed or Thursday but there may not be any wave close enough to the coast to matter. Right now it's too early to say but from Tuesday through Thursday looks to be a period to watch if you like winter weather.

Posted by: wjunker | February 2, 2011 2:40 PM | Report abuse

Come on spring! The little rodent did not see his shadow, and february is gonna be filled with high temperatures..So all of us snow lovers should just throw in our Snow Hope towels. I hope we have better luck getting a big "snow" storm, next year.. I refuse to consider the wet slushy slurpee that fell from the sky last wednesday, as a huge "SNOW" storm.. The only thing huge about it, was the traffic it caused.
At least with snowmaggedon we had a good solid excuse not to travel outside, because everything was closed..

Posted by: BELLASNOWQUEEN | February 2, 2011 3:10 PM | Report abuse

Come on spring! The little rodent did not see his shadow, and february is gonna be filled with high temperatures..So all of us snow lovers should just throw in our Snow Hope towels. I hope we have better luck getting a big "snow" storm, next year.. I refuse to consider the wet slushy slurpee that fell from the sky last wednesday, as a huge "SNOW" storm.. The only thing huge about it, was the traffic it caused.
At least with snowmaggedon we had a good solid excuse not to travel outside, because everything was closed..

Posted by: BELLASNOWQUEEN | February 2, 2011 3:10 PM | Report abuse

The wind arrived punctually. NWS said 3:00 and at 2:50 a 45 mph gust was recorded at Martinsburg/Shepherdstown. I do hope it backs off tonight. This is sort of unnerving.

Posted by: tinkerbelle | February 2, 2011 3:10 PM | Report abuse

I'm curious about when someone is going to comment on the number of tuesday/wednesday storms that we've had so far this winter.

Posted by: pgcoresident | February 2, 2011 3:16 PM | Report abuse

Awesome in depth break down Wes ! Also, really like the LONG RANGE outlook (Keep these coming) . Almost all of the media outlets wont go beyond 5-7 days,and even then its in the form of a sun/cloud/rain drop graphic.

Posted by: pseaby | February 2, 2011 3:31 PM | Report abuse

Around Feb 10 (200hr) the European 12Z run from today is showing plenty of cold air and a system, which it develops to far offshore right now. Also interesting this afternoon GFS Ensemble and this mornings European both show the NAO going Negative around the 10th. What do you think Wes?

Posted by: pseaby | February 2, 2011 3:43 PM | Report abuse

WES,

your forecast for friday/saturday is completely wrong. DC is going to get all snow out of this one with some mix at the beginning. Cold temperatures will be in the area by friday. Next Tuesday/Wednesday is going to be a major snow storm with up to 8 inches possible in the DC area.

Posted by: SNOWLUVER | February 2, 2011 4:12 PM | Report abuse

WE NEED SNOW, any chance we get a good storm this year?

Posted by: dannythe357 | February 2, 2011 4:21 PM | Report abuse

@dannythe257

Yes.

Posted by: AsymptoticUnlimited | February 2, 2011 4:29 PM | Report abuse

WES,

your forecast for friday/saturday is completely wrong. DC is going to get all snow out of this one with some mix at the beginning. Cold temperatures will be in the area by friday. Next Tuesday/Wednesday is going to be a major snow storm with up to 8 inches possible in the DC area.

Posted by: SNOWLUVER
___________

Your sn gives credence to your biased position, but unfortunately, Wes is not wrong. But, if you are referring to the weather front coming through NEXT week, then YOU'D be correct. THAT'S our next big chance of snow.

If this upcoming pattern brings snow our way, you will have been doing quite the snow dance my friend. lol....

Posted by: cbmuzik | February 2, 2011 4:52 PM | Report abuse

CBMUZIK

The NWS disagrees about tuesdays storm being our next big snow chance as they have it 43 degrees and 50% chance of rain.

I think snow lovers of DC's last real hoo-rah of a big snow chance will come NEXT friday. At least according to HM from accuwx that could be the big daddy. Its on the GFS as well.

Posted by: KRUZ | February 2, 2011 5:08 PM | Report abuse

Wow.
I am tired of this rain and sleet. I love winter because of the snow. If we aint gettin' no snow, bring on the dog days of summer.
I do enjoy the excellent CWG forecasts and explanations as well as the goofy posts by some of the WP readers!

Posted by: sobolasobola | February 2, 2011 5:08 PM | Report abuse

Looks like saturdays storm could at least end as snow?...

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/18/images/gfs_slp_072m.gif

Posted by: KRUZ | February 2, 2011 5:12 PM | Report abuse

Kruz, I think the surface on the 18z may be too warm for sticking snow at 72 hours, but 78 hours does look like it could end as snow esp N&W... maybe half an inch of slush?

Sterling's discussion mentioned freezing rain possibility early Saturday...

I appreciate CWG's continuing analysis...

Posted by: spgass1 | February 2, 2011 5:31 PM | Report abuse

@KRUZ
could you post a link to the gfs for that "big daddy storm"?

Posted by: bobdello01 | February 2, 2011 6:00 PM | Report abuse

bobdello

showing up as sunday but this is the storm i believe HM is talking about....

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/18/images/gfs_slp_252m.gif

Posted by: KRUZ | February 2, 2011 6:05 PM | Report abuse

Rain is fine on Saturday, but I sure would like at least one or two more snow storms. Us snow lovers got spoiled last year! Of course, I may have jinxed the whole thing - my daughter had a growth spurt and I just bought her all new long sleeve shirts. Spring is sure to be on the way. :)

Posted by: redsoxgirl | February 2, 2011 6:28 PM | Report abuse

@Kruz,

First, that is a map 252 hours in the future. Way too far to take too seriously. Second, that graphic looks to be a big RAIN daddy. But I hope I'm wrong and you are right. :-)

Posted by: pjdunn1 | February 2, 2011 6:54 PM | Report abuse

Wind in NW boonies still gusting near 40 mph. And NWS has the vampire cloud back for Friday night and Saturday for Harpers Ferry.

Posted by: tinkerbelle | February 2, 2011 7:06 PM | Report abuse

@pjdunn

This is the video i was referring to... http://www.accuweather.com/blogs/meteomadness/story/45278/a-look-at-the-next-storm-coming-saturday.asp

He also tweeted and sent a message on his facebook about NEXT fridays storm potential to be a big daddy. I personally think we are done for snow this winter. Maybe another inch to mix is the pipeline, maybe. I hope im right about that ;)

Posted by: KRUZ | February 2, 2011 7:33 PM | Report abuse

@Snowluver

Your post yesterday regarding Chicago and CWG's School cast, was seriously funny!!! I had tears of laughter pouring from my eyes.. You mocked the person with the post that spelled tomorrow wrong, by spelling it"tomaro"!!! LOL :)

Posted by: BELLASNOWQUEEN | February 2, 2011 9:18 PM | Report abuse

@Snowluver

Your post yesterday regarding Chicago and CWG's School cast, was seriously funny!!! I had tears of laughter pouring from my eyes.. You mocked the person with the post that spelled tomorrow wrong, by spelling it"tomaro"!!! LOL :)

Posted by: BELLASNOWQUEEN | February 2, 2011 9:18 PM | Report abuse

Im tired of all the half ( bad word) snow storms this year as well....1-4 inches..sleet ..light snow,,slush..etc...

bring on a good 12 inch snowstorm baby or let us go ahead and break out the shorts and t-shirts i say and head for the beach!!!

even last weeks commutagaddedon didt even get me out of work..we had 8 inches here but it was plowed well ahead of time...

WES..i know FEB is a snowy month here. Should we throw in the towel with the el nina around or is here hope yet for big one?

Posted by: BradFinWoodbridgeVA | February 2, 2011 10:07 PM | Report abuse

Agreed..yes, Wes what is the real scoop. I can take the truth. Throw in the towel? Quit refreshing? Or is there hope? Oh, I meant, SNOWPE?

Posted by: manassasmissy | February 2, 2011 10:48 PM | Report abuse

Now it's Macaroni for Saturday?

Posted by: manassasmissy | February 2, 2011 10:50 PM | Report abuse

Wind has really picked up here in Clifton. Gonna be hard to sleep with the siding rattling so much.

Posted by: pat-in-clifton | February 2, 2011 11:43 PM | Report abuse

The comments to this entry are closed.

 
 
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