Long, narrow bands of intense water vapor stream across the sky like rivers in the air. These atmospheric rivers can stretch thousands of kilometers and carry as much water as the Amazon. When they make landfall, especially against mountains, they dump extreme rainfall.

Most form over the subtropical Pacific and flow toward the west coasts of North America and Europe. A strong event can deliver a year’s worth of precipitation in a few days. The moisture is concentrated in a relatively thin corridor, often only a few hundred kilometers wide.

Forecasters watch satellite water-vapor imagery and model output for these features. Early recognition allows warnings for flooding and landslides. Not every atmospheric river produces disaster; many simply bring beneficial rain to dry regions.

Their strength and position shift with larger climate patterns.