Atmospheric Rivers: plumes of moisture that generally start in the tropic and subtropics. Usually associated with warm air (since warm air contains more water vapor than cold air). They dump precipitation when they interact with the hilly terrain of our region. e.g Pineapple Express
We're getting one tonight, but it's more westerly than the usual P.E., and thus the rainshadow will move southward making the north Sound virtually rain free. The mountains will get 5-10 inches of rain, increasing avalanche risks.