Saturday, November 20, 2010

Forget the Snow over Seattle--Its Heading to Oregon

Last night there was a burst of light snow, accompanied by strong winds, in the Bellingham, Whatcom County, San Juan Island areas...and some snow reached Port Angeles. The explanation is simple: moisture from a small low circulation rotated into the opposing cold flow of the Fraser and other gaps in the Cascades. Here are some snowfall measurements provided by the National Weather Service:

WHATCOM COUNTY SNOWFALL (INCHES)

BELLINGHAM 1.5(MILES)SW 3.0
BELLINGHAM 2.4 SW 2.3
FERNDALE 2.1 NW 1.5
BELLINGHAM 9.8 NE 1.4

SAN JUAN COUNTY SNOWFALL

WALDRON 1.1 NNE 2.6
LOPEZ ISLAND 3.9 NNE 2.0
ORCAS 0.7 NNW 1.0
FRIDAY HARBOR 6.2 WNW 1.0

CLALLAM SNOWFALL

PORT ANGELES 8.1 SSW 2.2
PORT ANGELES 2.5 SSW 0.9


Today there was a dramatic transition in much of the lowlands of western Washington as cool, dry northerly flow pushed south. The air above the Puget Sound lowlands is now cold enough for snow. Alas, cold is not enough...we need moisture...and it looks like that will not be forthcoming.

I waited to write this blog until I saw this night's runs, and to look at the probabilistic predictions from National Weather Service and the UW ensembles, as well as the European Center Global Model (the gold standard).

My conclusion, if the models are correct, the central Puget Sound region, including Seattle, will get little or any snow. But we will get extraordinary cold--particularly on Tuesday morning. On the other hand, Portland and Willamette Valley, will see the white stuff.

Here are some graphics regarding the current situation. First the precipitation probabilities from probcast...which uses an ensemble (a collection) of forecasts and then applies sophisticated statistical post-processing. High probabilities of precip (snow) in the Cascades, southern WA, and Oregon. Not much over Seattle and north.


And here is the snow forecast from the high-resolution WRF model for the 24h ending 4 PM Sunday. The Cascades and SW Washington get some light snow.



And here is for the next 24h. Forget most of western Washington for snow.

The models would really have to be in error for Seattle and the northern lowlands to get significant snow..which has happened. And there is still some uncertainty to the solution. But lets be honest, snow lovers will probably be highly disappointed. The cold is serious business though...anytime it gets below 20F around here, there is trouble. I expect large areas of the lowlands away from the water to get below 25F and a number of colder spots in the teens.

There is one group, of course, that likes supercold weather...plumbers. Freezing pipes are good for business. A few years ago, weather.com (the weather channel) was going for a crazy cold wave....a plumber called me up all excited...should he bring on more people to handle all the business? You can lessen their income by making sure your outside faucet don't freeze up and that you insure that pipes in crawl spaces are insulated or heated.

Finally, I should make things clear...making a good forecast is more than looking at a few model simulation plots. To do it right, takes not only a physical understanding of the situations that have produced snow, but judgment about which models are doing well, have done well in similar situations, the consistency in time of each model and between models, and today a careful study of the new technology of ensemble predictions. A good forecast takes quite a while to do.

19 comments:

Avalanche said...

The gold standard, lol. What do they know they that we don't. Cross your fingers for uncertainty and unpredictably. Hey, if a computer could predict conditions for 6 months advance, weather would be boring and meteorologists would be out of a job! So slow down your research at Udub!

kevinfreitas said...

Thanks for the update Cliff! Going to wrap up my spigots tomorrow. As always, keep up the fine work!

j said...

Thanks for the update. You're the official weather dude of Seattle's indie media :)

kermitizii said...

At Point Grey, next to UBC in Vancouver BC, there was 10 cm of snow last night. I actually went x-c skiing tonight outside my place next to UBC, great conditions, as the snow is now getting very frosty. Other places in Van had 2-4 cm. The storm last night was north of the border, and to the west of Vancouver BC.

linda said...

so its because of the low that is over oregon that is going to give chehalis south more snow than olympia north...
Its amazing how people are getting all freaked about this: We lived in Pullman long enough that even the big snow in 2008 was no big deal! I drove our taurus station wagon daily to McChord, after my hubby dug it out since his school in Onalaska was closed b/c of snow.

kass master said...

NOT COOL!!! ha was looking forward to some snow

natchrl8r said...

Honestly, the down-playing of the "light snow" in Bellingham is beginning to get to me. This is really quite serious. We had 2-4 inches, drifting deeper in some areas. It barely thawed and refroze to create extremely dangerous driving conditions. Not so bad if you are prepared and aware but it only takes one false move or another driver to wreck your day. Like Seattle in the past, Bellingham is woefully under-equipped or vigilant in mitigating the icy conditions. What would be a minor "light snow" event anywhere else in the country is life threatening conditions wherer the roads are un-plowed or sanded. With the lack of maintenance and freezing conditions lasting for days in Whatcom County, I would warn anyone heading this way to proceed with extreme caution!

Mattias said...

Seems like there has been a trend over the last handful of model runs to force things slightly further West, causing more over water trajectory for the low and giving us a better chance for snow. 6z NAM sure looks great for snow Monday all the way up to Seattle and a little North of there even. With all the model inconsistency with this feature on Monday I'm not sure how anyone can say anything for sure. We will just have to wait and see how this plays out over the next day plus of model runs.

BTW, the convergence sure worked out like I thought it would with the Southerly flow around the low and NE winds out of the Fraser. Bellingham saw 4"!

Michael said...

Hmmm... This kind of reminds me of a weather even about 10-15 years ago. I belive it was an area of low pressure heading for Seattle and at the last second went south leaving seattle without snow, but dumped on everyone south.

Or a couple of years ago when I low was sliding down the coast and was supose to slide into seattle, but instead slid down the coast and everyone lucked out...

So I guess things could change at the last second. I guess we'll find out tomorrow.

Thanks Cliff :)

Ben Randall said...

what about the North Oregon Coast

Imaflatlander said...

520a Sun - 98036 edge of Brier/Mountlake Terrace: sparse, small snowflakes coming down. Just enough to raise my raise my hopes in order for them to be dashed.

Brad said...

Had light snow near Ft. Lewis Sunday morning from around 2am past 6am. It was like small snow balls, not much larger than a fly's head. Sounded like sand hitting my windshield.

John Davidson said...

We live on Blakely Island (Kind of between Orcas and Lopez) and the NE wind has been howling through Peavine Pass since Friday afternoon. We got a solid 3" of snow, but the wind has been brutal. With the even colder (30F now) temps predicted is the wind going to get stronger (hope not)?
Thanks for the great weather information, really appreciate it!

Upupaepops said...

well I live in Redmond

it is just light enough to see out at 722

it is snowing lightly

sigh

My mind is just not ready for the chilly weather

Casual Observer said...

Bothell about 375 ft elevation -- very light dusting of snow (not frost) over the ground and plants. The flakes are dry little pellets that are widely spaced. They look almost like hail, but are flatter and shaped more like snowflakes.

bridgid10 said...

Well Cliff, we live on Vashon and have a dusting, perhaps we are the exception to the rule? LOL The rest of the day will see how the snow in the fickle convergence zone plays out today.
Thanks for all of your postings, you are the most accurate weather person I follow.
Cheers!

JayNorth said...

Natch - you are right. 2-4 inches in Bham creates dangerous situations, mostly because it turns to ice in the road and people here are horrible winter drivers (and mostly lack snow tires). I don't think anything Cliff was saying contradicts that.

On the other hand it is just a kick to read that there is 2-4 inches of snow, "drifting deeper in some areas." The humor is just in the choice of words. Back in NY we routinely had drifts that were 5 feet tall. Now sometimes out in north Whatcom County there are big drifts when there is significant snow and those Fraser Valley winds. But drifting with 2-4 inches is a hoot. I am sure anyone from a snowy region would agree. Sorry!

Thanks Cliff so much for this blog. I am an ecologist, moved here 10 years ago from the NE where I pretty much understood the weather. Here I have been confused about our weather most of the time. Your blog and book have helped a lot, though I must say I am still confused a good portion of the time!

Kevin said...

Hi Cliff,

To echo some of the other comments, the snow in south Bellingham on Friday night was far from 'light'. By my rough estimate, we had almost exactly 4 inches of snow fall in a 3 hour period, from approx 8 pm until 11 pm. At times, the visibility was down to a few hundred yards and the snow was piling up into drifts. Just posting this as a clarification.

Thanks a lot for the blog

Sandy Strehlou said...

Can anyone tell me if driving over Stevens Pass on Wednesday is a bad idea? We have four-wheel drive and good tires, but no chains. Any chance the pass will close? Help.