November 14, 2020

Heavy Snow and Tuesday's Offshore Low

Very heavy snow has fallen in the mountains, with several feet in the passes and above.  Current depths include:

41 inches at Mount Baker Ski area

43 inches at Stevens Pass

47 inches at Paradise at Mount Rainier

Paradise Visitor Center on Mount Rainier

And the latest UW WRF total snowfall between this morning and Thursday afternoon shows a lot more coming:  several feet more in the Cascades (see below).    And even decent snow in Winthrop and Mazama, where there is nearly a foot on the ground right now.

What about uncertainty in the forecast?  

Good question.  We always need to consider that.  Below is a "plume diagram" of the snowfall at Stampede Pass (4000 ft) for the many forecasts of the NOAA/NWS GFS ensemble system (called GEFS).  Looking at many forecasts, all slightly different, is a good way to explore the uncertainty of a forecast.  The black line is the mean of all the forecasts.

There is some uncertainty, but all the forecasts show bountiful snow, with roughly 25 inches more by next weekend.

Folks, the implications of this is clear:  there should be enough snow for several ski areas to open by Thanksgiving!   One concern for the next few days will be avalanches, considering the bountiful snow that is falling.

So get your skis ready...there will be plenty of snow.  If the gyms close due to COVID, healthful outdoor exercise may be available in the mountains.

And then there is the potential for a windstorm on Tuesday.  There IS a lot of uncertainty about that event.

This morning's UW sea level forecast shows an impressive system offshore at 1 PM Tuesday (see below), with a 967 hPa low.  Big pressure gradient and big winds--although a bit too far up Vancouver Island to give Seattle big winds.

Is there uncertainty?  A lot.  

The vaunted European Center model has a large, excellent ensemble of many forecasts.  Here is plot of the mean sea level pressure of all the ensemble members and the locations of of the low centers for all the forecasts.  Mama Mia!  They are located all over the place and of different central pressures.  So big time uncertainty....and none of them positioned to give Seattle a major blow. 

Bottom line:   lots of white stuff in the Cascades is a good bet.  Big windstorm on Tuesday--no so much.

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  1. A very informative post. Great to hear that the ski destinations are finally going to open up. My sister was constantly asking me to check that on the Climacell app. I will forward this article to her.

  2. "So big time uncertainty....and none of them positioned to give Seattle a major blow."

    Would not some of the more southern projected locations for the low center have potential to continue towards Seattle? Or are they all expected to continue up the coast?


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