During the past weeks, the Pineapple Express has been running in one way or the other, bring warm, moist air to the West Coast. The atmospheric moisture forecast for 1 PM (below) shows the story, with a stream of large moisture content heading from the islands to our region. This warm air has not been good for the local ski areas, many of which have opened with marginal conditions.
The last two weeks have been extraordinarily warm, with the minimum temperatures of most days falling to roughly the average maximum for the day. Here is the departure of the average temperatures from normal for the last two weeks for the western U.S. Amazing. Quite a few places have been 12-15F above normal, particularly in Idaho and Montana. But Washington and Oregon have many areas 4-8F above normal.
The West Coast has been wetter than normal, particularly California, where many locations received 200%+ of normal precipitation. The good news is that the big reservoirs like Shasta have begun to fill.
Here is the Mt. Shasta reservoir levels....big upswing (dark blue line), but still below normal (blue shading).
But the big weather story for the Northwest is the major regime change that is about to occur, with a major ridge developing over the eastern Pacific bring drying and cooler temperatures. To illustrate, here is the upper-level flow forecast for 4 PM on Friday. BIG RIDGE. And one that will bring cooler air into eastern WA, Montana, and the central Plains. We will finally be cut off from the Pineapple Express.
Take a look at the Climate Prediction Center 6-10 day temperature forecast. Blue indicates colder than normal.