Major Weather Transition Ahead

During the past week or so, the Northwest coast of the U.S., from the central California to Seattle has pummelled by one Pacific Storm after another.  Looking at the percent of normal precipitation (see image below) for the last 7 days, you can see northern California has been particularly hard hit, with some places getting 800% of normal precipitation.  The reason:  a persistent trough over the northeast Pacific and an amazing frequency of atmospheric rivers extending into the northern part of the Golden State.

But there is a very positive side to this deluge:  with large precipitation additions recently, both snowpack and reservoir levels are near average over most of California, for a good start to the water season. California needs water.  Eventually, when human-forced global warming hits, they will have  real water problem.  But not this year.

But things are going to change soon, since virtually all the major models are forecasting a major flow transition this weekend, with a high-amplitude  upper-level ridge developing over the eastern Pacific (see example for Saturday at 4 PM).  This ridge is far enough offshore so that we will be in cool, occasionally showery flow, but it will be WAY drier than the last week. 

 This is a favorable pattern for snow, with far lower freezing levels.  Finally, it should be cool enough so that Snoqualmie will get enough white stuff to open.  Here is the 72 h snow total from the UW WRF model.  Over a foot in the Washington Cascades, a feet over some favored locations.

This pattern continues into early next week.  Take a look at the upper level map for Monday at 4 PM... an even bigger ridge.  But don't expect that we will be cloud free and completely dry...there is plenty of flow over us and weak disturbances will southward down the eastern flank of the high.

Anyway, this will be an opportunity for things to dry out a bit and winds should be more modest for the entire region.