Sunday, November 22, 2015

Cold Air, Snow in the Mountains, and Strong Winds in and Downstream of Mountain Gaps But Little Lowland Snow

We have an interesting few days ahead of us--weatherwise at least.

This morning (Sunday) many locations got into the 20s F west of the Cascades and the teens east of the crest.

Over the eastern side of the Columbia Gorge winds gusted to 50-80 mph in exposed locations like Crowne Point (see wind plots)
Crown Point Wind


Max gusts around Portland the past 24 h

As you can see from the surface pressure map at 8AM (pressures are solid lines, colors are temperature at low levels), there was a very large pressure difference in the Gorge...driving winds towards the west.  On a lesser scale, a similar phenomena was occurring in Snoqualmie and Stevens passes, with winds gusting to 30-40 mph around North Bend, WA.


The latest model runs show a cold front moving across our region tomorrow afternoon.   A front with only limited moisture.  Temperatures will be too warm for snow over the lowlands on Monday, but the higher terrain will get several inches to roughly a half foot (see forecast of total 24h snow ending 4 AM on Tuesday).   Maybe some light snow over parts of Whatcom County.


On Tuesday, much colder air will be moving in, but unfortunately most of the precipitation will be over for western WA, WITH SOME EXCEPTIONS!   Strong flow from the northeast will extends out of the Fraser River valley and push against the northern Olympic Mountains, producing moderate snow (up to a foot) at Hurricane Ridge and lesser amounts extended to sea level around Port Angeles (see map of the snow during the next 24 h below, ending 4 AM Wednesday). Some snow showers are quite possible over northwest  and southwest Washington.

But there is something else.  As the low system moves by, there will be upslope flow over the eastern slopes of the Cascades, producing moderate snow along those slopes including Wenatchee, Leavenworth, Winthrop, and the Okanogan areas.  The Cascade crest will get a few inches more.   Good for Mission Ridge and Stevens Pass.

But if you are the Mayor of Seattle you can probably rest easy--the Metro area should get very little snow.

And now time for caveats.   There will be cold air around on Tuesday.  If our models were off by a few hundred miles regarding the position of the incoming upper level trough and associated surface low, a few inches of snow in Seattle is possible.  But at this point it is unlikely.

And for those in NW Washington, the winds and wind chills on Tuesday and Wednesday will be FIERCE!.  Consider the forecast gusts for 7 PM Tuesday--up to 60 knots over the eastern Strait of Juan de Fuca.  Bellingham will got 30-50 mph gusts.


Cold, sunny conditions will spread over our region from Wednesday to Saturday. Perfect for a walk or run before you Thanksgiving meal.

6 comments:

Pierre Sodbinow said...

If a large persistent ridge were be in place during this time of year, it seems to me that the quality of air will eventually degrade. In addition, if low stratus develops, it will be hard to burn off due to low sun angle. I hope you are right that cold, sunny conditions will prevail Wednesday through Saturday.

Rod said...

Gorgeous day today, Cliff. Nice to see the crystal clear Olympics from West Seattle with the snow capped peaks...

Just last Tuesday, the 10th of November, I saw 10 or so Orcas off Mee Kwa Mooks park. That was a first for me...though I did see Namu in the mid-sixties at the Seattle waterfront.

Thank goodness the Feds put capturing Orcas to a screeching halt not long after that disgusting era...

-Rod

David B. said...

“And now time for caveats.   There will be cold air around on Tuesday.  If our models were off by a few hundred miles regarding the position of the incoming upper level trough and associated surface low, a few inches of snow in Seattle is possible.  But at this point it is unlikely.”

In other words, a plausible scenario exists by which this “no snow in the lowlands” forecast might bust. It probably *won’t* bust, of course —- but it might. This is precisely the sort of information that more weather forecasts need, particularly the complex and difficult cases like lowland snow in the Pacific Northwest.

Ricky Poole said...

Doesn't look like snow to me. The percipitation will run out before the cold front pushes through. Not too much snow in the mountains either...kinda looking like we aren't getting snow that will help open and keep open resorts.

Thecatguy93 said...

The 72 hour snowfall forecast looks like a joke now compared to yesterday morning. Much less, especially along the east slopes of the Cascades where the moderate snows it was showing for Wenatchee, Leavenworth, Winthrop are almost totally gone now. How can a forecast change so drastically in a 24 hour period?

richard583 said...
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