Friday, December 19, 2008

This weekend storm



I have waited to write this until I have taken a careful look at all the observations and model output. The storm coming in Saturday evening and Sunday morning is potentially much more disruptive than Wednesday's event...and includes both snow and wind.

But before I talk about it how about some fun?...take a look at the latest satellite picture (attached). You see the narrow cloud band over the Sound? That is being forced by a convergence of land breezes on both sides of the Sound over the water. Land breezes occur when the land is colder than the water and the air flows from land to water. Last night with snow on the ground, the land was colder than the relatively warm Puget Sound. The air converges and rises forcing the land breeze convergence zone cloud band. An image from a webcam at the UW shows it (see pic) and if you really like this kind of thing...look at the video (http://www.atmos.washington.edu/cgi-bin/latest.cgi?webcam0_movies). I explain such features in some depth in my book.

Ok, lets get serious. An energetic and wet Pacific weather system is now approaching our coast and will start impacting us on Saturday...particularly later in the day. It will bring a low pressure trough to our coast and will force moist, warmer air above us...producing clouds and precipitation. As pressures fall along the coast on Saturday due to the approaching system the pressure difference across the Cascades will greatly intensify (low pressure west, high pressure associated with the colder air east) and southeasterly winds will increase near crest level. As a result, winds will accelerate over the Cascades, particularly across lower areas in the mountains. The result--very strong easterly winds along the western slopes of the Cascades, particularly around Enumclaw, Black Diamond, North Bend, and Maple Valley. The winds could easily gust to 40 to 80 mph, with serious potential for loss of tree branches, falling trees, and power outages. The winds will start accelerating tomorrow morning and will be powerful by afternoon and peak during the early morning hours Sunday (see graphics for 4 AM Sunday) Weaker easterly winds...but still notable.. will extend towards the Sound.
But the winds are only a warm up. Now lets talk about snow.
The precipitation shield from the incoming system (actually its warm front) will reach the Puget Sound lowlands around dinner time. We will have sufficiently cold air for this to fall as snow. There should be a huge east-west difference in the amount of snow that falls tomorrow night and Sunday morning. The easterly downslope flow causes drying. On the other hand the easterly flow will rise as it approaches the Olympics--producing greatly enhanced snow. As are result, I would expect a huge snowfall gradient by say 4 AM on Sunday AM--with the western Cascade slopes and far eastern suburbs only getting a few inches of snow. (see the graphics of 24-h snowfall from the latest high resolution forecast model). Seattle and west shore of Puget Sound communities should receive 2-6 inches, and the Kitsap hit by 1-2 FEET. If you are living west of the Sound this will be serious. Better buy some food and be prepared to hunker down. The heavy snow will continue there until at least 9 AM Sunday.

But there is so much more.... This includes powerful southeasterlies in the western portion of the Strait that will develop tomorrow evening...with winds gusting to 50-75 mph and substantial snow at the western exit of the Strait. Lots of snow in the mountains--at least a foot. And the potential for freezing rain south of Tacoma and over SW Washington late in the event as warm air moving in aloft causes a layer of air to be above freezing.

This is classic active weather situation where numerous major local weather features occur at once...the complexity caused by our local terrain...that is why we love it here!

52 comments:

SeaRod said...

Great! I am eagerly awaiting your comments on the coming storm. Meanwhile, I'm tuned in to KUOW.

Ellie Fields said...

Cliff, love your weather reports. Snow is tough for the commute but great for skiing- for a geeky comparison of the early-season conditions at Seattle resorts as compared to California and Utah, see
http://www.tableausoftware.com/blog/early-season-skiing-finding-snow
I think you'll be entertained.

zephyr said...

Me too I think I have checked this blog 20 times this morning. I live on the sound in North Kitsap and I am particularly interested in how far this wind event may extend and how I should prepare along with my neighbors.

seattle wedding photographer said...

I can not find your book in stock anywhere.
Nobody can keep it in stock.
We need it before Christmas.

Lindsey said...

Interesting to listen to you on KUOW just now. You refer to Wednesday/Thursday's system as "wimpy," but it laid down a whole lot of snow. If we only ended up with 2-4" in Seattle from this next storm, that's less than much of Seattle got yesterday.

llpowwow said...

Cliff, when you mention Kitsap County for the big storm on Saturday night and Sunday, do you extend that south to Gig Harbor and the Key Peninsula?

This is critical for me as I need to leave for a flight to New Zealand on the 24th and need to figure out if I am going to be able to drive from my rural Key Peninsula location in Vaughn to the airport, or if I need to make arrangements to stay at a friends house in Tacoma for the several days prior to the 24th. Thanks for any weather guidance you can give that would help me make this decision.

JewelyaZ said...

I am worried about my former mother-in-law who is supposed to fly home to England Saturday evening at around 6 pm. Anyone have any guesses if the wind will be bad enough then to ground her plane, or will they take off in the teeth of the gale and escape it aloft?

BillC said...

Hi Cliff:

Love your KUOW broadcast and Blog/Website. Hopefully getting your book for Christmas. I'm another weather junkie you can add to your list. Have a Davis Wireless Vantage Pro2 @
48.11795N
122.83043W
2 miles +- West of Port Townsend with their WeatherLink software (Mac) that I download to my computer. Will be interesting to see how this weekend's wind event will register here.

natchrl8r said...

Dang! I missed the radio show by 5 minutes! I am loving this blog though.
For the person wondering if they should leave, I'd say "Better safe than sorry." I wouldn't depend on Cliff to peg your exact forecast to make plans. He's a meteorologist, not a fortuneteller. Sorry to speak on your behalf, Cliff. Just don't want you to take the blame if someone thinks you made a bad call. Keep up the great work!

Ms. Jill said...

The mention of strong winds in the foothills causes me to ask: where, exactly are the foothills? Can anyone clarify this for me? Just the thought of strong winds Anywhere makes me a bit on edge.....

happyrailtrails said...

I'm trying to convince my brother and family not to fly here from New Jersey to go to the Seahawks-Jets game. They just don't understand how Seattle reacts to winter storms. I'll send him Cliff's blog.

Cliff Mass Weather Blog said...

Seattle Wedding Photographer...a number of local barnes and noble stores still have the book...you can check on their web site to see. Everyone else should be back on line sometime next week.

natch...the broadcast is always available on the KUOW web site.

Anonymous said...

What cities are considered the foothills? Woodinville? Bothell? Issaquah?

Anonymous said...

god i love the weather! cliff, you are awesome!

JewelyaZ said...

Most people consider towns like North Bend and Enumclaw to be foothills... sometimes Maple Valley, Snoqualmie, and Duvall are lumped in there too. Issaquah can get "foothills weather" in spots when things are bad. It will be interesting to see what Cliff says, too, but that's how I interpret the foothills.

Anonymous said...

Cliff- any insight on what we can expect re: amount of snow and wind speeds in the Olympia/Thurston county area this weekend? Also, do you think the storm will hit down here on Saturday night or Sunday morning?Thanks

Anonymous said...

the nws said that the coast and sw interior are going to be hardest hit.. do you agree?

Anonymous said...

Am I crazy to think about driving to Portland/Vancouver on Sunday mid-day??? We had such perfectly laid plans...

natchrl8r said...

Thanks, Cliff. I listened to the podcast on KUOW. I'm still left wondering what the effect of this coming storm may be on the Bellingham area. Sounds like most of the action is further south and in the gaps in the Cascades. Can we expect significant precipitation this far north? I expect whatever we get will be all snow. The bigger question remains: what will travel conditions be like early next week? I'm not convinced I'll want to drive to Mazama for the Christmas Ski Trip on Tuesday. Wait and see...

Anna said...

Hi Cliff,
Will we get winds in Seattle, too, or is the major danger snow? I'm just not sure what to expect from this coming storm, and what I need to do to prepare.
Thanks,
Anna

Anonymous said...

Natchrl8r, The National Weather Service is extending the Winter Storm Watch to Bellingham. Here is what they say: A SIGNIFICANT SNOW EVENT IS POSSIBLE. GIVEN THE AMOUNT OF OVERRUNNING MOISTURE AND HIGH QPF TO SNOW RATIOS...I FELT IT PRUDENT TO ADD THE EVERETT / BELLINGHAM ZONES TO THE WATCH.
THE NEW NAM-12/GFS ARE
SHOWING RATHER IMPRESSIVE QPF AMOUNTS FOR THE METRO AREAS WITH THE QPF TO SNOW RATIOS INCREASING AS YOU GO NORTH. AMOUNTS OVER 4 INCHES ARE LIKELY AND POSSIBLY IN EXCESS OF 6 INCHES SO THE WATCH LOOKS GOOD.

Also, the models are trending a bit cooler for Christmas. Not saying it will happen, but for us in Bellingham, a white Christmas looks very possible. I am in Sudden Valley, we have about 12-13 inches.

mainstreeter said...

Anonymous, I wouldn't venture south to Portland after 10am on Saturday. They are forecasting the front to arrive then and if they have a "silver thaw" freezing rain event, it will be messy for a couple of days or so.

From KATU weather site:
A WINTER STORM WATCH HAS BEEN ISSUED FOR MUCH OF OUR AREA INCLUDING THE PORTLAND METRO FOR SATURDAY AND SUNDAY. SNOW WILL BECOME POSSIBLE BY NOON SATURDAY AND IS EXPECTED TO TRANSITION INTO FREEZING RAIN BY EARLY SUNDAY MORNING. ICE ACCUMULATION WILL BE POSSIBLE THROUGH THE DAY SUNDAY. WARMING TEMPERATURES AND A TRANSITION TO RAIN LOOKS POSSIBLE SUNDAY EVENING. THIS STORM HAS THE POTENTIAL TO BRING DOWN TREES AND POWERLINES. PLEASE STAY UPDATED.

natchrl8r said...

Thanks, Sudden Valley. I had read the warnings and noted that they added us up north. I guess I can only extrapolate from that as all forecasts center on Seattle Metro unless there is a specific event focussed somewhere else. I'll count my blessings. When I lived in the Whatcom Foothills the NWS stats came from Abbotsford, BC in the Fraser Valley and Weather Blunderground, which was available on my cell service, gave stats at 6000' for Deming!

natchrl8r said...

Perhaps I just need a tutorial. Looking forward to getting Cliff's book... I don't know what increasing qpf ratios are and I wasn't sure if the Metro Areas referred to Everett/Bellingham or Seattle.

Sean said...

Hi Cliff,

Thanks again for keeping these posts--great drama!

I have one request for a future blog on a quieter day--reading through the NWS Discussion, reference is made to several different computer models used in the prediction process (GFS/ECMWF,NAM-12, etc). It would be interesting to know a little more about these models, how they work, etc.

Many thanks!

Norm said...

Cliff, thanks for this blog. I hope you have the energy to keep it up as I never tire of hearing someone intelligent talk about NW weather. Upcoming windstorm: I saw in a NWS discussion a comparison to similar “wave action” event in Dec 2003. I think I remember that one. I lost a maple tree in my yard in Newcastle…a mile from Lake Washington, and hardly the foothills per se. How likely on Sat/Sun that damaging gusts come down that far west?

Lindsey said...

Cliff,

Interesting how you characterize this as a "classic" active weather situation, whereas I see the following wording from the current NWS Forecast Discussion:

"This is a rare and very complex weather situation."

JayDee said...

Cliff:

I'd always called the land-cooling convection clouds "Cloud Trains" because they form over the Sound so often during cool weather. Sometimes you can even see them form on the Hood Canal, and rarely I can see the one down the Georgia Strait/Admirality Inlet from here in Alki.

Thanks for explaining the Cloud Trains.

Joseph Ratliff said...

Excellent post once again Cliff...

It looks like I am in for another "pounding" of snow here in Lacey, WA. :)

cornbread said...

Dang, looks like I am going to get pummeled by the winds here in Maple Valley. The last time (2003-4 I think) this situation developed in the winter gusts were to 80mph and power was out for over a week. It literally looked like a tornado had touched down there was so much damage, trees tossed like matchsticks.

Laurel said...

finally, a blog for someone like me, who really wants to know more and that educates us and talks to us as if we can understand what is going on! Thank you, great site. I learned about you from a friend on Facebook!

Anonymous said...

Could someone please post the link to Cliff's report on the KUOW web site? I'm not having any luck tracking it down. Thanks.

wholeclothdesigns said...

Thanks for the snow graphic, Cliff. We already have about 6-8" of snow at our house in Olympia and from the looks of your map we will likely double it by Sunday AM.

natchrl8r said...

http://www.kuow.org/program.php?id=16553

Cliff's spot is towards the end of this program. Good luck!

Joelle said...

Hi Cliff (or anyone else who can help). I'm heading up to Canada tomorrow (Saturday) around noon. We plan on coming back on Monday (mid to late afternoon)... Tuesday at the latest as we need to be back before Christmas.

I live in Renton so I'll just be going up the I-405 to I-5 corridor. I assume the interstates will be well plowed. I bought some chains today just to make sure.

With the incredible weather this weekend, should we just stay home and cancel the trip? My concern is mostly coming back -- we don't want to get stuck in Canada. So my timeline: Leave for Canada about noonish, head back to Renton around 3:00'ish on Monday. I noticed that it may start raining Monday as it warms up, so I'm hoping that means the snow and ice melts to a wet but safe commute.

Thoughts? Thanks so much!

Kevin said...

natchrl8r asks: "I don't know what increasing qpf ratios are and I wasn't sure if the Metro Areas referred to Everett/Bellingham or Seattle."

As anyone who listens to the weather radio knows (chant along!): the Metro area is "Seattle, Tacoma, Everett and the vicinity". Bellingham is a seperate area: the Northwest Interior in NWS speak.

Quantitative precipitation forecast (QPF) is the prediction of the amount of precipitation that will fall at a given location in a given time interval.

Depending on the weather conditions a given amount of rain will result in an certain amount of snow. The figure that connects these two numbers is the snow to liquid ratio.

So in some cases (think wet sleet) 1 inch of rain is equal to 1 inch of "snow". But for fluffy dry snow the snow to liquid ratio is much higher (10:1 or even higher). Yet another complication of predicting snow.

It seems that the NWS folks are worried that the snow ratio will be high with this storm so you could get a lot of snow for a given QPF.

For example see

http://www.theweatherprediction.com/habyhints/346/
http://sanders.math.uwm.edu/cgi-bin-snowratio/sr_timeetc.pl?site=KBLI

One URL perhaps needed is to the American Meteorological Society glossary: from AABW to ZDR.

http://amsglossary.allenpress.com/glossary

FWIW: Quite a few people ask questions that can be answered just by looking at the graphics Cliff posts. Click on them to get the big version so you can see the details. Look for where you live (try another map with cities on it and look for coastline or mountain features to find your way).

Reading the charts is not too difficult: look for wind barbs for wind speed and direction; contour lines and shading for the other parameters. Check the upper right corner and the bottom for the key. The title gives you a hint of the time period and content of the chart.

Anonymous said...

Hi Cliff - - - First, thank you so much for your blog and reports on KUOW. Your nuanced and balanced discussions are much appreciated.

Secondly, do you have any specifics on the upcoming event and its effect in the San Juan Islands? Things seem to have a way of affecting us here in the islands differently than the surrounding areas. At the very least, I'll be leaving my chains on for the weekend. Thanks for all you do.

Anonymous said...

I guess Cliffy must've gotten stuck in traffic?

JewelyaZ said...

Kevin,
Thanks for the educational links! I knew some of the things you posted about, but not all of them, and weather and weather predicting is pretty much endlessly fascinating to me, so I was glad to see these resources.

Anonymous said...

Or maybe Cliff actually has a life:-)

Thanks to Cliff for the great KUOW spot and this wonderfully informative blog. Thanks to all the posters for the additional info and entertainment!

Jason said...

Best message is all is the very real need to be PREPARED. We now have predicted: several inches of more snow, high winds, very cold temps.
Two years ago we had a major wind event (also in mid-December) and power outages with 200,000 homes affected. Food, water, warmth are essential and it isn't up to government or service agencies to provide. It is up to you.
Thanks to Cliff for the warning/forecast.

Cliff Mass Weather Blog said...

All...I very much appreciate all the positive comments...it looks like I am not the only lover of NW weather! I know I can't describe all the local impacts of the approaching weather system...it would take pages and pages...but if you look at the graphics I am including you can get an idea of how snow and wind will vary around the region. ..cliff

Anonymous said...

New reader here! I just love the NW weather, but sometimes it can get a little scary. I live in Enumclaw, but lived in Maple Valley when the 03 storm hit. Are these winds to be comparable to the 03 storm? or worse?

Thanks!

Anonymous said...

^^^^^^Sounds like it could be a real similar event to 03 when I watched old growth firs splash into Lake Wilderness from my deck. I am not looking forward to this, nothing says "Happy Holidays" like a tree through you roof.

I will keep people updated as long as there is power, which probly won't be to long.

I would sign in as cornbread, but the site won't let me now.

Debbie Sladek said...

I'm really enjoying your book.

On Tuesday night I was reading the chapter about snowstorms. Last night, it was windstorms. I'm watching the weather very closely this week and it's really enlightening having your book at hand.

Your blog and KUOW spots are also very helpful. Thanks for helping my understanding of our wild and whacky northwest weather.

Mackie Images said...

Very cool site. As an avid backcountry skier, I'm always trying to find detailed forecasts. Predicting weather here is quite hard, but this site will surely help! In November we were complaining about the lack of snow...now we can't even get up into the mountains to enjoy it!

Laine said...

Hi Cliff,
My local bookstore can't get your book until January but that's okay. I am glad so many people know about it!
It is so great how everyone is contributing to the blog. Here's my tip:
People can find forecasts for specific locations in western Washington at http://www.wrh.noaa.gov/sew/
Just click on the place you are interested in.
Hope I don't lose power this weekend--I want to follow all this weather talk on the internet!

Liembo said...

Walter Kelly of Q13 on their 10 o'clock pm newscast just emphatically said (twice) that Seattle could see 8.5 inches of snow on Sunday, talk about sensationalism?

Anonymous said...

Dear Liembo:
Sensationalism? Maybe, maybe not. As Wednesday's non-event demonstrates, predicting weather around here is a crap shoot.

Anonymous said...

No offense to whoever posted above. But Walter kelly is like the worst meterologist on tv.

Anonymous said...

Kevin noted: "As anyone who listens to the weather radio knows (chant along!): the Metro area is "Seattle, Tacoma, Everett and the vicinity."

Reminds me of when I used to work at KUOW in the '80s/'90s. I would read the forecasts for "Seattle-Tacoma and Vicinity," and would occasionally ask out loud "where exactly IS Vicinity? I can't locate it on the map." It became a running gag with our listeners for a short while.

Cliff, it's always a treat to hear and read your interpretations of our weather. Thanks for turning us all into weather geeks!

Karin Hill said...

Thanks for your wonderful weather commentary, Cliff. It's very useful and I'm learning a lot and plan to buy your book. I don't understand the charts very well but do plan to use some of them as quilt designs.
Karin