(CNN) An atmospheric river event known as the "Pineapple Express" is forecast to bring a prolonged period of wet weather and the potential for avalanches to Washington and Oregon beginning Sunday. How a Pineapple Express formsAtmospheric rivers are narrow corridors of the upper atmosphere that transport intense moisture from a large body of water onto land, like rivers in the sky. This particular atmospheric river event is special in terms of where its moisture comes from -- Hawaii. The Pineapple Express originates near Hawaii and travels across the Pacific Ocean to the western coast of North America. "When it reaches the West Coast, the Pineapple Express can dump as much as five inches of rain on California in one day," according to the National Oceanic and Atmospheric Administration.

Source: CNN February 21, 2021 10:02 UTC