Definition

Atmospheric rivers are long, relatively narrow (on average 400-600 km wide) regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics. These flowing columns of condensed vapor move with the weather and are present somewhere on the Earth at any given time.

Description

When the atmospheric rivers make landfall, the water vapor rises and cools and is often released in the form of rain or snow.

 A strong atmospheric river can transport an amount of water vapor roughly equivalent to 7.5 to 15-times the average flow at the mouth of the Mississippi River in the United States, which is the 15th largest river in the world as measured by discharge volume. The Mississippi discharges nearly 16,800 cubic meters of water per second into the Gulf of Mexico.