In the last few years meteorologists have become increasingly aware that some of the most intense rainstorms on the West Coast are caused by concentrated bands of moisture that pour water vapor into the region. These bands are called “atmospheric rivers” because they act like a conduit to bring high volume rain events to California, Oregon and Washington. In the past they’ve sometimes been called the “pineapple express” because the plume of moisture often seems to originate from somewhere near Hawaii.
Earlier this week, Dr. Cliff Mass, an atmospheric science professor and blogger at the University of Washington, describes the phenomenon and talks about how the expected upcoming event may help bring drought relief to the region (link). In another blog, Dr. Jeff Masters of Weather Underground discusses the research that is being done to understand the dynamics of these systems and gives a forecast of what folks out there should expect. NOAA also wrote a story about the current research effort here.
The maps below show today’s flow of moisture into the Pacific Northwest and the 3-day rainfall totals that are forecast to occur with this storm.