Tuesday, November 22, 2016

Heavy Mountain Snows Ahead

Update at the end!

There are going to be some happy skiers, snow shoe enthusiasts, and snow lovers this weekend, because quite a bit of snow is going to fall above 3000-3500 ft during the next week.  A combination of a series of wet systems and temperatures just cold enough for mountain snows will result in several feet of fresh snow at higher elevations.

The infrared satellite image this morning looks promising.  A modest frontal band, associated with a band of rain at lower levels, is now crossing the coast.  But that is not what has gotten me excited...it is what is offshore:  a broad region of instability (the mottled broken clouds) that is associated with cold air over warmer water.   These kind of cold convective showers are the big snow makers of our region.


Let me show you some model output for the next week--and keep in mind there is always uncertainty in the forecast.   However, this kind of general pattern is far more predictable than the exact path of a small low center.

I will start with the total snow accumulation (snowfall) for the next week of the European Center Model (graphics courtesy of WeatherBell).  Wow.   The Cascades, the Sierra, the Olympics, and the Mountains of southern BC get three feet or more above roughly 4,000 ft.

 A close up of NW Washington shows the promising situation more clearly.



 How about our higher-resolution UW WRF, driven by a completely different global model (the NOAA/NWS GFS)?  Here are the 72h totals (ending 4 PM Friday).  Huge amounts (3+ feet) in the Olympics and southern BC mountains.  Much of the WA Cascades does well.  But far less in Snoqualmie Pass (4-5 inches)--which is good considering how many people will be crossing over I90 for Thanksgiving.


For the next 72 hr, as the jet stream sags southward, the snow action shift shifts towards Oregon and California, with nearly a yard of snow falling from the south Cascades to the Sierra.


The large scale upper level pattern for 4 AM Monday has a La Nina look with broad northwesterly flow over the Northwest and high pressure offshore.  Radically different than the pattern of the last month, with a deep trough over the NE Pacific..  For the sake of mountain snow lovers, lets hope it holds.

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Update:   Here is the 72h snowfall from the latest UW WRF run at ultra-high resolution (4/3 km) for western WA.  Some places in the Olympics get over 40 inches, as does Mt. Baker and Rainier.  Low and warm Snoqualime Pass does poorly (only a few inches).     I suspect Baker will get enough to open.


11 comments:

John said...

The location of a offshore high pressure ridge is the critical factor in any Northwest snow situation.Just hope that a high stays centered offshore at 140-150 W longitude.If it moves closer to the West Coast, snow lovers are screwed.....

Bryan Black said...

I just want to see the omega block with the polar jet stream plunging down over the PNW. These neutral to slight La Nina late fall/winters tend to be pretty big snow makers. I recall 2008-09 and 2013-14 being ridiculous down here in Oregon.

Puffin said...

This chart of polar sea ice is sobering.

J said...

Exciting news! Bring on the snow, especially lowland snow.

Two questions...

Any news on the updated GFS Model?

This next question comes from a complete lack of knowledge on how modeling systems work and how they are run through supercomputers. Ever wish you could get a UW CRAY Supercomputer and use MPAS to provide results on the Pacific Northwest Environmental Forecasts and Observations page!? I do!

Maybe a CRAY supercomputer wouldn't be necessary over a smaller forecast area like the Pacific NW...

measuredmass said...

Cliff, with the incoming mountain snow, please consider directing skiers and snowshoers to the Northwest Avalanche Center's website for avalanche-safety information. Thanks!

www.nwac.us

Unknown said...

Cliff,

Has your longer-term view changed materially in less than a week?

Nov-16: "the persistent troughing off the west coast and inland ridging, and the latest model runs suggest it will remain in place during the next few weeks. "

Eric Blair said...

Could we please just once have no one come on here and begin screeching all over again about GW? My goodness, what a Debbie Downer. Try to enjoy life, for once.

Grant Gunderson said...

I bet baker opens Friday....

sds said...

Grant
If they do, I'll bet you'll be up there taking your fantastic photos. Maybe even get some in Powder Magazine!

Westside guy said...

We'll be heading over "low and warm" Snoqualmie pass... so I hope it lives up (down?) to its billing from your post!

Jason said...

I bet you're right!