Weather Tidbits: Atmospheric River

This Weather Tidbits explains what is an atmospheric river. An atmospheric river is a large, narrow & continuous band of moisture; similar to an actual river but in the sky. They originate normally from the tropics into the mid-latitudes. It consists of a giant band of water vapor (on average 200-400 miles wide) that pushes inland. When the moisture moves inland, the mountains force it upwards; where the moisture cools and condenses, producing rain, and if cold enough, snow. Depending on the duration, AR’s can produce very heavy snow, flooding & mudslides.

Atmospheric rivers that originate around the Hawaiian Islands are known as the Pineapple Express. The West Coast sees them less frequently but are more impactful than on the East Coast, where they originate from the Gulf of Mexico. Atmospheric rivers are also categorized in a five-level scale that include both the strength & impact which considers both the amount of water vapor transported & the duration of the event. The scale begins from a Category 1 being the weak & primarily beneficial to Category 5 being exceptional & primarily hazardous.