An atmospheric river is a long, narrow plume of moisture that travels from the ocean over the land. They are one source of heavy precipitation during the winter months on the west coast of the US. Check out this video on atmospheric rivers for a cool visual:
Atmospheric River Animation; January 2017 (Credit: NOAA/ESRL/PSD)
So what is the connection between an atmospheric river and the pineapple express? Looking past the movie credits, a pineapple express (a non-technical term!) is one example of an atmospheric river that originates over the Hawaiian Islands and brings warm, tropical water into California and over the mountain ranges into Nevada. We make the distinction because the origin of water into the plume is important and can influence the type of precipitation that falls. Either way, each type of atmospheric transport brings its own influence to the west coast, and we’re excited to watch it make landfall.