Heavy Rain and Massive Snow

It was a warm, cloudy day here in the Northwest with large contrasts of rain (see figure below of the observed 24-h precipitation ending 7 PM Thursday): over 3 inches in the Olympics, but only light rain over the lowlands, and a few sprinkles across the basin of eastern WA.   Why so little over the Cascades but lots over the southern slopes of the Olympics?  The key reason is that the flow aloft was southerly (from the south) and you can't get good upslope on the Cascades from the direction.  But you can get good upslope over the south-facing slopes of the Olympics.

But the real precipitation story is to our south, over southern Oregon and northern CA, where some locations got over four inches (pink color) and over two inches was commonplace.  But this is just the beginning.

 With a large low center center over the NE Pacific and persistent strong flow pushing eastward to our south, northern CA is going to get hammered during the next several days.
Flooding is inevitable.

Take a look at the latest UW WRF model precipitation forecast for the next 72 h:  huge amounts, including over 10 inches in "favored" upslope locations.  The Olympics and north Cascades are also wet.

 From weather satellites that measure atmospheric moisture, we can see the narrow plume of water vapor...an atmospheric river..that has been feeding the California rainfall.

 Tonight I will premiere a new figure created by UW WRF modeler Dave Ovens:  72hr snowfall!  Lots (feet) of snow over the mountains of BC, and the higher elevations in the Cascades do very well indeed (foot or more).  Most of the accumulation at pass and ski area elevation will occur later in the weekend as the freezing level drops and the wind direction becomes more westerly.   The Sierra Nevada range goes to white (literally)--more than 45 inches of snow at higher elevations!  The folks at Tahoe must be salivating. 

Here is a close up of the 72h snowfall ending on Monday at 4PM for Washington.  Baker and Rainier will be buried.  Stevens, at least a foot.   Snoqualmie will pick up a half-foot or so.  Not sure whether it will be enough to allow them to open.