Amospheric rivers are wide-reaching plumes of moisture that act like a firehose, tapping into warm, moist air from the tropics that storms can then unload as drenching rainfall and heavy snow over land.
These types of storms are winter hallmarks across the West Coast. Not all are harmful. Weaker atmospheric rivers deliver much-needed rainfall and snow to the region during the wettest months of the year.
This rainfall and snow is vital to western water supplies. It fills up water reservoirs that are critical resources during dry, hot summers.
But atmospheric rivers can quickly become more hazardous than helpful. Excessive rainfall unleashed by these potent storms increases the chances for flooding, particularly when a series of storms happen in sequence with little time to dry out between.
Last week’s atmospheric river broke multiple rainfall records across California and triggered road closures and water rescues.
Atmospheric rivers aren’t exclusive to the West Coast. They can also impact the eastern US and happen frequently in parts of Europe, Africa, Australia and New Zealand.