Thursday, December 11, 2008

A Difficult Forecast

Things have changed. The forecast models, which indicated substantial uncertainty yesterday, appear to be locked on to a solution--one in which a strong low center will move SOUTH of Seattle, not north, as previously predicted (see attached sea level pressure forecast for tomorrrow at 4 PM). This will have a huge impact on the forecast tomorrow. Forget strong southerly winds along our coast and in Puget Sound. Forget the strong westerly surge in the Strait of Juan de Fuca. Thats history now. Just so you can appreciate how difficult this forecast problem is.... consider that the low doesn't even exist now...but will form shortly. That this low is forecast to amplify explosively. That a 100 mile error in its position can radically change the forecast. But as I will note, there is no doubt about cold air coming...the big issue is snow.
So this is how I see it. Today will be cloudy and dry. It better not rain...the weather radar is broken (I swear that hardware knows when challenging weather is coming.... similar to the fact the copy machines malfunction when you REALLY need them). The low will develop rapidly tomorrow, spreading rain over the area tomorrow, starting in the late morning . When the low was going north of us we didn't have to worry about snow, because there would be strong southerly and southwesterly flow. Now we have to worry.
I think it will be too warm for snow over much of the lowlands initially...except for one place...southeast of the Olympics around the lower hood canal and the Kitsap. If you live there, better be prepared. Second, as the air gets colder later in the day there is the possibility of snow reaching the ground where showers are strongest--and the higher elevation you are the more probably it gets. However, initially there will be strong easterly flow that should keep the wesern side of the Sound snowfree. As the low moves east northerly flow will increase..resulting in upslope flow and potential snow immediately NE of the Olympics...like the Sequim area (the opposite of the normal rainshadow there). Then after midnight a puget sound convergence zone could form...providing light snow over central puget sound. We will get a better idea about the above threats as the higher resolution runs become available later this morning. On Saturday, strong northeasterly flow will be pouring through the Fraser River Valley into Bellingham and NW Washington (see second figure of near surface wind speeds). Very strong, cold, dry air.
The mountains will get snow...but less than the old storm track. Perhaps a foot in the pass. And this may not be enough to initiate downhill skiing.
No matter what, our region will switch to unusually cold, dry air. It will be like moving to Vermont or the upper midwest. Highs will only reach the low to mid 30s from Sunday to Tuesday....but it will be dry. Even sun. No seasonal affective disorder. But you need to protect pipes and plants.

11 comments:

Joseph Ratliff said...

So Cliff...since this forecast seems to be so "elusive" because of the variables involved that you mentioned...

In the Olympia area, with this low predicted to now come in to the south as mentioned...would the previously forecasted wind speeds be reduced?

And...what is the possibility that this forecast would revert back to the original models with it coming in north?

Joseph

Keeping one's head above water said...

what does this mean for sw washington ( ie centralia/chehalis)?

Citroen said...

Your 10:O9 blog said to "forget" all the forcasts for strong winds along coast, etc., but minutes later the NWS issued a Marine Weather Message with gale warnings in effect most of Friday for the
Strait, Admiralty Inlet, Puget Sound, etc. Can you explain divergent views?

Cliff Mass Weather Blog said...

Citreon...I meant strong southerly winds with the low...we will get strong northerly coming out of the Fraser and Strait of Georgia...cm

phred said...

Sounds like Parka Boy better suit up for his "Artic Blast 2008" coverage

Citroen said...

Whoops! Guess I skimmed right over
that "southernly"--thank you.

Let It Snow said...

As a meteorologist, why do you call the snow and cold "threats"? And do you realize that some people have been affected with Seasonal Affective Disorder because of the huge amount of abundant sun we've had the past 8-9 months? Hopefully we get some good snow and avoid the threats of sun and warm temperatures.

Rick Eilman said...

Cliff,

Given the developing trends you noted, would you expect treacherous travel conditions on Sunday on highways 104-101 from Kingston to Sequim?

Rick

Cliff Mass Weather Blog said...

Answers to questions:

Kingston to Sequim might have snow.

There is little chance the low will head to our north now...but there is no certainty of anything!

Centralia/Chehalis could well have snow showers tomorrow evening and on Saturday morning

Scott K said...

Hey Cliff,

I'm hoping to find out your reaction to the winter storm watch that was just released by NWS for a large part of western washington.

I agree more with your predictions and am not expecting much snow, if any at all on Friday.

Has anything changed in your models since this morning to help support the recently released winter storm watch?

Thanks!

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