Bountiful Snow But Warm Rain Is On The Way

The promised snow has fallen in the Cascades, allowing a number of ski areas to open, including Stevens, Crystal Mountain, Whistler, and Mt. Baker.  In fact, our current snow pack is well above normal.

Here is plot from NOAA showing the the snow depth last year (left) and this year (right) for today (Nov 17).  A LOT more snow this year than last.

The Northwest Avalanche Center did an analysis two days ago (see below) and the numbers are impressive, with Hurricane Ridge in the Olympics enjoying 500% of normal snow depth for the date.  Mount Baker 209% of normal and Mission Ridge at 325% of normal.  And we have had more snow since then.

So a very good start to the snow year in the Northwest mountains.

But snow lovers have a problem....some warm and wet weather is coming, with freezing levels rising well above the Cascade passes.

Here is the forecast for temperatures above Sea-Tac Airport.  The y axis is height and the x axis is time (increasing to the left in UTC/GMT).  The solid blue line is the freezing level (0C level), winds are indicated by the barbs, and relatively humidity with color shading (green is moist).

The freezing level is below 5000 ft overnight tonight and moist showery conditions are in place (more snow).  Tomorrow will be dry (no shading).   But then there is trouble...a strong current of moist air comes in later on Sunday...an atmospheric river...with the freezing level zooming up to around 7500 ft.  Rain on our precious snow.   Then the atmosphere cools a bit on Monday and then a VERY warm air mass comes in on Tuesday, with the freezing level reaching about 10,000 ft.  Not good.

The forecast total atmospheric moisture values in vertical columns (see below) shows impressive values of moisture streaming into the Northwest at 10 AM Tuesday--a substantial and warm atmospheric river.

And the 72h total precipitation ending 4 AM Wednesday is enough to send erstwhile Californian's back to the Golden State, with over 5 inches of warm rain over the higher terrain of Washington, Oregon, and California.  

With lots of rain and melting snowpack, flooding will be a concern by mid-week, with rivers such as the Snoqualmie and Skagit being forecast to reach flood stage (see below).  So be prepared if you live or work near these rivers.

 Thanksgiving week is traditionally the wettest and stormiest of the year..and it doesn't look like it will disappoint in 2017.




from Cliff Mass Weather and Climate Blog http://ift.tt/2itzK15