Monday, February 21, 2011

Snow and Cold are Coming

Update 10:30 PM: Lots of report of ice pellets, graupel, and wet snow in the convergence zone and in the foothills. New model runs in...still very threatening for snow
Update 7:15 PM--the convergence zone has formed and I can hear ice pellets on my window!


I am going to go out on a limb now...I think most of you ...even those in the lowlands ...will see some snow before the week is up. And much colder temperatures.

A front is now crossing the coast, with a switch to northwesterly flow behind. You can see this on the latest surface chart:

You can see the lowering of the clouds and start of precipitation over the Olympics in this video:




Colder air will move in behind the front, causing the atmosphere to be less stable (more convective showers) , and there is a good chance of a convergence zone over Puget Sound forming tonight and tomorrow morning behind it. The freezing level will be low enough that if the CZ has sufficiently intense precipitation, wet snow could reach sea level with the zone.

So don't be shocked by some flakes during the next 18h or so. This system will SURELY bring snow to the mountains...in fact, enough to improve the skiing a bit (6-12 inches). I was skiing in the pass on Sunday and lets say it needed to be freshened up a bit. Here is the 24-h snow ending 4 PM Tuesday. And yes, it is showing some snow over the eastern Puget Sound lowlands...places a high elevations and away from the water.


But this is just a warm up (really just the opposite!!). The air will get colder on Tuesday into Wednesday and then an upper level trough will move towards us from the north (see map). This is close to a classic upper air snow configuration. Not quite perfect (little too much extension over the Pacific), but close enough. And by the time we get to Wednesday we won't have to worry about being cold enough to snow.

Associated with this upper trough will be a low pressure center that will form in the lee (south) of Vancouver Islands. (map). The real primo cold air will be locked in the interior of BC, blocked by the mountains.

Virtually all the models are on board with this solution--enough that I think it has a good chance of it happening (YES, there is always uncertainty in a forecast). Virtually all indicate strong NE winds will exit the Fraser starting on Wednesday...and then it gets interesting and more uncertain.

There is little doubt that there will be some snow showers with this system, but serious snow demands more. If the low remains offshore of the north WA coast the easterlies will move down the Strait and some of them will plow into the Olympics, hitting the north Olympic communities with snow. Those retired folks will have to switch from golf to x-country skiing for a while! If the low moves southward, then southerlies moving up the Sound could plow right into them, give decent lowland snow over the Sound. In any case, there will be an interface between the northeasterlies and southerlies that will produce a significant snowfall somewhere, most probably over NW Washington.

Here is what the WRF model run at the UW is showing for two 24-h time periods--ending 4 PM on Wednesday and Thursday:

You can see the heavier snow associated with the interface--stretching across Whidbey Island to the north Olympic peninsula.

I was looking forward to giving my talk at Ivar's on Wednesday evening....so I hope the snow does its typical mirage act.... But the bottom line is that exciting things are possible during the next 48-h..so be prepared. I know Jim Forman is.

25 comments:

TVN said...

Yay - snow in the mountains! You should have gone to Crystal or Stevens. Cliff. I guess we are still below average but there is plenty of snow for skiing. I can't believe the forecasted highs in the mountains - burrrrr....

Anne said...

Thanks so much for your informative posts, Cliff. I really enjoy them. I live in Oak Harbor - fingers crossed for one more good snow event before winter heads off for the year...

a progressive crank said...

We just drove down from Mt Baker and it was snowing heavily there all day, diminishing along 542 all the way to Glacier, and then rain all the way to Seattle. The streets were dry not 20 minutes ago but I see (and hear) that it caught up with us.

I wouldn't mind some lowland snow but after experiencing Baker, the passes are going to be pretty weak sauce, no matter how much they get.

Hal said...

Am I right in thinking this has been an usual year for both cold and the chance of snow? I did a quick search, and we've been flirting with snow (and less often, getting it) since November. Three months of on-the-cusp snow conditions in a place that (it seems, to this relatively new resident) to have 1-2 well defined snow events a season just seems like... a lot. Is that feeling accurate?

DeAnne said...

Its a hailing here at the Central Washington Coast - Moclips, Seabrook, Copalis. West winds 17 mph 41F BAR 29.92 steady

Would like to see one last snow before my favorite time of year...spring.

Steve said...

The shower that moved through Shoreline from about 6:50 to 7:45pm, which had mixed rn/sn, dropped the temperature from 40 to 36.5, with 0.08" of precip. Nice!

Ferdi said...

This almost looks like a situation where a stationary low parks over my island and dumps a bunch of snow. Don't know about the NE outflow winds. They don't really have the upper level jet stream support. But they'll probably be moderate to strong in any case. Not too thrilled about this weather but if it's going to get nasty it might as well do it in a big way.

cprimm said...

Now this is good forecasting!

Warmbowski said...

Some nice heavy sleet in Broadview, right now.

Dale said...

Update: Just saw Jim Forman in (in)famous yellow parka on 10 o'clock news! Yet another spot-on forecast by Professor Mass!

Thompsonized said...

Snowing hard in Ellensburg....and from the WSDOT cams, looks like here to Northbend at least will not be a fun commute tomorrow.

dissolved girl said...

Btw, did you know about this copy cat blog?
http://cliffmasstldr.blogspot.com/
He claims he's summarizing your blog.

Will said...

i just went for a drive from Bellingham halfway to Lynden on the guide meridian and there is about a half an inch on the ground up there. not snowing though. once you get into Bellingham, there's nothing

Will said...

Just drove from bellingham to Lynden. There is about half an inch of snow on the ground north of the Bellingham border. Not snowing any more though, looks like the band has passed.

Megan said...

It's been hailing for the last hour over here in Issaquah.

Wx Enthusiast said...

No "threat" for snow here in Bellevue this week, just an exciting chance of it! I'm not threatened by it one bit..

Super said...

Winter Storm Watch is now up for everybody Wednesday-Thursday.

I'm just south of Mukilteo and will be tickled if I can squeeze out 2-3 inches, even with business meetings Thursday.

Jim said...

3 miles NNE of Monroe, 400' elevation - woke to about 1/2" of graupel on the ground; now snowing as of 8:10 a.m. The convergence zone is right above us! Love the blog Cliff!

Thompsonized said...

Between Thorp and Cle Elum near white-out conditions, saw jack-knifed semi and a flipped pickup truck

analogkid said...

Snowing quite heavily along the highway 9 corridor from about Lake Stevens to Arlington. Has been on and off this morning, and pretty steady for the past 30 to 40 minutes.

Charles said...

We had a nice 90 minutes this morning of white fluffies (just south of Paine Field, a bit over 500' here on my hill). Just a dusting on a ground (currently 32 deg.) but a prelude, maybe.

Dyanne said...

South Whidbey is currently getting dumped on. Almost 2 inches here since 7:30 this morning. Roads (off the highway) are slick and treacherous. However per the various web cams the rest of lower Puget Trough from Lynwood south looks like a lovely day!
I may have to miss my UW class tonight if I can't get off the island in one piece.
Can someone direct me to a NOAA or other site that shows me real-time what's happening here in the convergence zone....so I can track the extent of expected snowfall today to make a wise decision to head off to the land of higher learning. thanks

Mark said...

Cliff - Could you do an explanation sometime how graupel is formed? Weird stuff...

Gentian said...

hailing at 7 am in Port Townsend, changed to snow at 10, still snowing hard at 11:30 am - switching between flakes & pellets

Gentian said...

woke up to hail at 7 am in Port Townsend, hailed off and on, then at 10 began snowing & is coming down hard now - switching between flakes and pellets. I can see the blue hole of the "snowshadow" off to the north.