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 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.