Saturday brought record-breaking daily precipitation to a number of western Washington and Cascade locations, with some 24-h totals getting above 4 inches. As I will show, several NW rivers have hit flood stage and slope failures are being observed in vulnerable locations (like the infamous rail stretch from Edmonds to Everett.
Yesterday was a beautiful example of the precipitation effects of atmospheric rivers: relatively narrow currents of high water vapor content that can stretch thousands of miles northward out of the tropics and subtropics.
Let me illustrate with two images: the first, remotely sensed total water vapor content observed by U.S. weather satellites. This product, produced by NOAA NESDIS, shows very high values of water vapor in the tropics, where warm air can hold lots of water vapor, and a narrow--but juicy--extrusion of high values stretching from near Hawaii to our shores. Yes...this is also called the pineapple express.
A simulation of a similar quantity by the UW WRF model shows this narrow moisture plume quite clearly.
With the heavy snow pack of last week melting quickly at lower elevations and torrential precipitation, the local rivers are reaching bankful or flooding; take a look at the current flooding map provided by the NW River Forecast Center. Moderate floods (blue color) are fairly unusual in March.
Showers will continue today and into Monday, but then high pressure will build in, bringing sun and temperatures in the upper 50s to perhaps 60F. Be prepared for springtime warmth.