What’s an atmospheric river? A pineapple express? AP explains the weather phenomenon

Associated Press

The storm that pummeled California this week was fueled by an atmospheric river, a plume of moisture that extended over the Pacific to near Hawaii. Atmospheric rivers are long and relatively narrow bands of water vapor that form over an ocean and flow through the sky. They occur globally but are especially significant on the West Coast of the United States, where they create 30% to 50% of annual precipitation. They are linked to both water supply and problems such as flooding and mudslides. Most atmospheric river events are weak. But powerful ones can cause extraordinarily wet weather.