Atmospheric River on the Way

Friday Afternoon Visible Satellite Photo---you can see the Pineapple Express already forming!

We have had quite a bit of heavy shower activity over the lowlands as well as snow in the mountains, but a period of heavier rain, particularly in the mountains, is on tap for later this weekend.

The first part of Saturday will actually be quite decent, but the action starts later that day as an unusually strong and well formed warm front pushes north across the region (see graphic).

Behind the warm front there will be a shift to strong, warm ,moist southwesterly flow that is connected to the subtropics--known as an atmospheric river...or as we call it here, a pineapple express.

This figure shows the amount of moisture in the vertical for Sunday at 4 AM. You can clearly view the narrow plume of moisture associated with the atmospheric river.


This strong plume of moisture will intersect our regional mountains, dumping substantial amounts of precipitation, particularly over the Olympics and N. Cascades.
Here is the 24-h rainfall for the period ending 4 PM Saturday....when the plume of moisture is mainly south of Washington. For those living in Washington State, if you want to do something outside over the weekend...do it before 3 PM on Saturday!

And here is the next 24-h. Serious precipitation over the Olympics and N. Cascades, with some amounts reaching 5-10 inches. A clear flood threat.

At this point, this event is no record-breaker, but it will bring serious rain and much warmer temperatures. Rain will fall on all that nice fresh snow in the mountains, SERIOUSLY contributing to a significant avalanche threat later in the weekend. Backcountry travel should be avoided then.