Large Snowfall will Hit the Cascades and Olympics

8 AM Sunday Update

The cold air was a bit delayed, but it is here now and the models were correct that the snow level would descend quite low.  Here a picture from Peter Benda, looking out over Cougar Mt.

And Stevens Pass is quite white right now:

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One of the best snow situations in a long time will hit the our regional mountains during the next few days, with some snow even reaching the lower terrain slopes.

Enough snow that will assure pre-Thanksgiving openings of a number of our local ski areas.

Let me start with the exciting stuff first.  Here is the predicted 72-h snowfall map for our region from the UW WRF system.

 Over two feet of snow over the north Cascades and the Olympics, with large amounts also over the mountains of British Columbia the and Oregon Cascades.

What is so stunning about this plot is that the snow extends to lower elevations...not sea level, but certainly down to around 1000-1500 ft.

This snow will fall on a decent base, as shown by the NOAA snow analysis for Saturday AM, which indicates healthy amounts (up to 20-30 inches) over the north Cascades and southern BC.

You may ask, why are we getting so much snow, during an El Nino year?  

Actually, El Nino years can bring decent snowpacks overall (down by about 20%) and El Nino effects often don't become profound until after the new year.   The current large scale atmospheric circulation is very much NOT an El Nino one.   For example, the upper level (500 hPa) forecast for tomorrow afternoon shows a big ridge north of Hawaii, with a deep trough over the western U.S.

El Nino years tend to produce a TROUGH in the same location... practically the opposite (this is shown in the figure below that provides the typical anomaly(difference from normal) of 500 hPa heights).

Major snow action will occur tomorrow as a low/trough moves past us, with cool northwesterly flow invading our region.  The map below shows the heights, winds and temperature around 5000 ft (850 hPa).  Northwest winds and cool temps (greenish colors) over and upwind of the Cascades.  Major snow producer.

Let me show you something new...our uber-resolution (1.3 km) WRF forecasts.

Here is the 24h total ending 4 AM Sunday.  Lots of snow in the north Cascades and Olympics. (1-1.5 ft).  Even the tops of some of the Issaquah Alps get it.

But the next 24h  (ending 4 AM Monday) are really something different (see below).  Snow from 1000 ft on up and even some snow getting near sea level south of Tacoma.  Amounts are modest (4- 8 inches).   Not much in the Olympics.