Monday, November 15, 2010

Is it Going to Snow Over the Lowlands?


Several of you have asked the potential for cold and snow this weekend, and this morning the National Weather Service put out a special statement regarding the possibility of a change to more winter-like conditions. And today, I got several calls from the media about it. And yes, the local TV stations are already talking about it online and on air. It is never good to get excited about snow too early--there are a few ways to get snow in the lowlands and so many ways for it to go wrong.

Anyway, we are now close enough to the weekend, and the models are in good enough agreement, and I am comfortable talking about what I see happening.

Bottom line: forget lowland snow this weekend but lots of snow in the mountains this week. Strong NE winds will blow through the Fraser Valley into Bellingham and NW Washington and colder air will spread over the region on Sunday and Monday. Clear evidence of the classic La Nina pattern. Maybe snow on late Monday or Tuesday, but too early to be sure. At this point, the Mayor can keep his snowplows in the garage and Jim Forman of KING TV can get his famous parka dry cleaned this weekend. And there will be loads of active and interesting weather during the next week!

But lets start with tonight. A low pressure center is now passing north and northeast of us, bring a strong N-S pressure difference and gusty winds (see image). During the past hours winds have gusted to 30-40 mph over the area, with some minor damage. Nothing special in November. Perhaps more special are the stronger (30-65 mph gusts) winds predicted for tonight and tomorrow morning over the eastern slopes of the Cascades. My lights are flickering right now and my Uninteruptable Power Supply (UPS) is going on and off!

But the weather fun is just beginning!!

During the next two days the upper level pattern is going to change radically--to one reminiscent of many La Nina winters--one with a very high amplitude ridge over the eastern Pacific and troughing and cold air in our area. Here is the situation on Wednesday morning aloft. Huge N-S ridge extending to the Aleutians and a high-amplitude trough to its east.
At the surface, there is a strong low center NW of the tip of Vancouver Island and REALLY cold air move southward into northern BC.

On Wednesday and Thursday trough and low slowly slip southward. And a strong,cool, moist flow hits the Cascades and Olympics...the result? Several FEET of new snow at pass level and above (see one 24-h period below ending 5 AM Thursday). Good for Thanksgiving skiing!

But then the weekend. The low slowly weakens and moves south. No cold air over us on Saturday. On Sunday at 4 AM the surface pressure pattern and low-level temperatures (shaded) and winds (the barbs) are shown below. The cold air is still mainly stuck in British Columbia--with one exception---air starts flowing through the Fraser River Valley into Bellingham and NW Washington, accompanied by strong NE winds (see figure)

The problem for snow lovers is that the precipitation over the weekend falls as rain over the lowlands since the air is too warm. And then when cold air moves in later on Sunday , things have dried out. Here is the predicted snow for the 24-h ending 4 AM on Monday. The only snow is over far NW Washington and southern BC. Remember this is sustained winds..really roughly 20 minute sustained winds..you must multiply by at least 1.5 to get gusts.


The situation changes on Monday and Tuesday, but that is too far out to be sure about anything. The cold air will be in place and showers could bring snow in a convergence zone or other feature. And the upper level pattern looks much more like the canonical snow pattern. So keep tuned. And consider that there is still some uncertainty for the forecasts over the weekend...we are still days out and a modest shift in positions of some features could have a significant impact.

By the way, there was a lot I didn't mention...like strong SE winds over NW Washington on Wednesday and Friday..and the strong coastal winds with the low on Friday. Or the strong westerly wind surge into the Strait of Juan de Fuca tonight. My colleagues at the National Weather Service will be worn down when this week of active weather is done!

30 comments:

Chris Christensen said...

Everyone here in Ellensburg has been talking about the windstorm all day. Supposedly gusts to 70-80 all along the eastern cascades tonight until the morning, but it is dead calm outside right now. A little confused, maybe it'll start picking up later.

SNOWMIZER said...

We are still 4-5 days out from this, and the new 00z model begs to differ on your conclusion. This it starting to remind me of 2008 a bit. But we shall see!!

mjgrota said...

sure must be nice to have those extended run products to look at this far in advance. This will be an interesting study to see how well the guidance verifies. Hope you will blog on that once the event passes. It's time to end the myth that guidance beyond 48 hours is not to be trusted for macro and some mesoscale applications.
Too back the interactive meteogram tool is not working.

MBeebe said...

Cliff,

If I head up to North Cascade Nat'l Park on Saturday afternoon, am I likely to encounter snowfall?

Ben Burditt said...

The 00z GFS says otherwise. Sorry Cliff, but I've got a feeling you'll be eating your words come Monday.

Joseph Ratliff said...

And don't forget the wind:

Issued by The National Weather Service
Seattle/Tacoma, WA
9:28 pm PST, Mon., Nov. 15, 2010

... WIND ADVISORY IN EFFECT UNTIL 1 AM PST TUESDAY FOR THE INTERIOR LOWLANDS FROM MARYSVILLE SOUTHWARD INTO THE SOUTHWEST INTERIOR AND WESTWARD INTO THE LOWER CHEHALIS VALLEY...

THE NATIONAL WEATHER SERVICE IN SEATTLE HAS ISSUED A WIND ADVISORY FOR THE INTERIOR LOWLANDS FROM MARYSVILLE SOUTHWARD INTO THE SOUTHWEST INTERIOR AND WESTWARD INTO THE LOWER CHEHALIS VALLEY... WHICH IS IN EFFECT UNTIL 1 AM PST TUESDAY.

*

* SOME AFFECTED LOCATIONS... MARYSVILLE... EVERETT... SEATTLE... BREMERTON... SHELTON... TACOMA... AND OLYMPIA

* WINDS... SOUTHWEST WINDS 25 TO 35 MPH WITH GUSTS TO 50 MPH.

* TIMING... VERY WINDY CONDITIONS WILL CONTINUE UNTIL ABOUT 1 AM... THEN WILL SLOWLY DIMINISH EARLY TUESDAY MORNING.

* IMPACTS... WINDS OF THIS STRENGTH WILL CAUSE SOME WEAKER TREES TO FALL AND WILL RESULT IN LOCAL POWER OUTAGES.

smokejumper said...

I'm a little angry/confused tonight. The official forecast called for 70mph gusts tonight!High wind warning starting at 7pm. Downed trees and powerlines expected. All day I was scratching my head? Im only 25 but I have never read such a bold forecast.

I just stepped outside, and its perfectly calm. Wenatchee, Eburg, Yakima 6, 9, 11 mph respectively.

Just noticed on your chart that the isobars have a slight N - S gradiant. Maybe thats sparing the east slopes the wind so far.

SNOWMIZER said...

The 00z shows a major snowstorm in the puget sound area around monday and tuesday!!

Weatherfreak said...

Cliff, you are like the Grinch that stole Christmas on this one! I want snow this weekend and you just burst my happy bubble. Ok, so it's still early, November snow is bonus in my book anyways. Hopefully, this will not be the first time this pattern presents itself. The CFS Long range model has our coldest weather setting up January thru March. BTW, just had a 51mph gust here in SE Auburn! You can bet someone lost a tree with that one.

Mattias said...

Well if the 00z comes even close to happening all us snow levers will be overjoyed. It is probably overdone though, at this point it is an outlier being so extreme. 00z Euro will be interesting.

Evanheaven said...

I love your blog, Cliff! But, FYI, your MM5 model currently shows about 2-6 inches of snow over the central Sound on monday: http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d2_x_snow3+///3

Jen said...

@smokejumper no complaints about lack of wind here in Tacoma... most of the North End of the city is out of power, as well as large swaths of West and South Seattle.

Scott K said...

From Lake Stevens,

This wind storm came out of nowhere. We've been having very strong west winds all night, getting very very strong until about midnight, seems to have leveled off now. I wish I knew exactly how strong they are.

All I know is, of the past 3 years I've lived in Lake Stevens I have not seen winds this strong from the west, it's quite a change from the normal south and east winds. :)

As for snow, I've lived here too long to trust anything other than 24 hours notice when it comes to snow predictions, even then 24 hours is a bunch optimistic. Regardless, I put my studless snow tires on my subaru today (in preparation for heading over the pass to Yakima next week). Bring on the snow. :)

Don't forget to wrap your outside pipes this weekend!

Chris Christensen said...

Still dead calm in Ellensburg, so much for the damaging winds overnight...

Maria said...

spent an out up on my deck in Fremont watching the clouds whip by and Azure flashes of lighting! I have never seen that shade of blue before amazing storm!

Lindsey said...

I certainly wouldn't mind someone explaining with some detail the "00z" that some of you are discussing. Is it likely what "While it looks rather unlikely at this point -- it should be noted though that some runs of both the GFS and European have shown a second shortwave dropping into the Pacific northwest from the north...reinforcing the cold air and bringing moisture as well" in the current NWS Discussion is referring to? . . .

Christopher said...

If you want to see an amazing wind chart, check out the Whidbey Island (KNUW) weather conditions from last night (Monday night). At 6:56, wind 3mph. At 7:56 wind calm. Eleven minutes later, at 8:07, wind 31, gust 54. From calm to a 54 gust in 11 minutes. That's quite a change!

Cliff Mass Weather Blog said...

All,
There were strong winds on the eastern slopes. Wenatchee got to 64 mph for example. A very good forecast by the NWS and the models.

FYI-- the 00z mentioned by some comments is the a model run starting at 0000 Greenwich mean time.

..cliff

silly1 said...

Oh no!! Fortunately (because i finally have a job after two years of being on the shadow unemployed rolls) or unfortunately, I now must move my family 3200 miles across the country to Boston NEXT WEEK. Should we be taking a route more southerly than the shortest I-90E route?

Kevin Purcell said...

Maria said: "Spent an out up on my deck in Fremont watching the clouds whip by and Azure flashes of lighting! I have never seen that shade of blue before amazing storm!"

That's not lightning ... that's downed electric distribution cables shorting and transformers blowing up. Copper does have a very pretty color when vaporized!

Tuesday AM AFD is currently pessimistic for snow on Monday given the latest model runs. As Cliff points out you need everything to line up just right to get the liquid to solid phases transition around here. We will have some of the cold but not enough precip.

But still that's a long, long way out (6 days!). We'll see when we have 72h or 48h mesoscale forecasts for Monday.

How does the skill of WRF-GFS prognostications in predicting PNW snow fall off with time? There must be some work on this subject.

Sermonti said...

With all this focus on the potential for cold weather and snow, last night's Western Washington windstorm was a real forecast failure.

Aaron Hill said...

Why was there such a large difference in wind speeds around the northwest last night? I got a few gusts in Bothell but it lasted all of 10 minutes and was calm the rest of the night. I'm still trying to figure out why the winds were so strong for such little time...Do you have some wisdom to this Cliff?

Anthony said...

Yes, the wind in Federal Way was absolutely EXCEPTIONAL and I've stayed up all night for every wind event to hit Washington since 1994...nothing can touch the wind we had last night, it was terrifyingly strong to the point of being completely deafening moving through the greenbelt...I heard dozens and dozens of tree falls (some of which shook the ground)and saw hundreds of transformer flashes. Also, my anemometer which is completely sheltered between two houses (argh, on the lee of a hill) recorded its all time peak gust in eleven years at 32mph, too bad it only takes readings every three seconds :/ anyways, it was the most amazing thing I've ever seen!

Islandgrl said...

Last night on the south end of Vashon Island, the wind was INTENSE. I would guess gusts of 50 mph. I could hear branches breaking and trees coming down. Of course the power went out around 9pm. I watched the clouds race across a clear sky and a half moon with the glow of transformers blowing up across the water in Tacoma. Quite a night.

Josh said...

I thought the classic la nina pattern doesn't show up till January beyond.

Chris and Amy's story said...

The windstorm on Monday evening was amazing here in Skagit County. I don't remember a wind storm during all of last winter that had such strong winds... at least up here. And it seemed to be out of nowhere!

Neil said...

The windstorm last night here in Port Townsend was remarkable not so much for it's intensity (we get gales out the Strait pretty often in the winter) but for sudden-ness and the torrential rain that started it. One minute calm, the next sheets of rain and howling wind out of the west. There was lightening along with the blowing transformers that we could see on the back side of the storm as it blew east. The rain only lasted perhaps ten minutes and then it cleared off but the wind really howled for most of the night.

CC said...

snotel sites at Stevens Pass recorded gusts of 78mph@4900' and 117 mph@5400'last night. Given the number of trees downed at pass level and to the west, I'm inclined to believe these were not anomalous readings.Unlike the last big windstorm up here this one happened before major snow so PUD didn't have to worry about avys and we already have power back.

mjgrota said...

I am in the4 Monterey CA area and got a paniced call from my wife last night from the Mill Creek /Bothell area. Very strong winds and heavy hail. Told her winds would be not be too severe and to tell Foreman to get off the roof.
On a serious note: Winds measured by the air quality network showed the highest hourly averaged wind to be it the Tacoma tide flats. 26 mph. That is pretty significant for a sustained wind over the course of an hour.

linda said...

its weird here in chehalis: the 1st windstorm came in and it was windy, but nothing to be stressed out about and the same with the one this morning.
Is Chehalis in this topographically alternate universe when it comes to wind ( not to floods or snow like in 2008/09).