Cloud River

Atmospheric rivers—often referred to as “cloud rivers” due to their long, narrow bands of concentrated moisture—can transport staggering amounts of water vapor, sometimes exceeding 15 times the average flow of the Mississippi River.

A strong atmospheric river can carry over 1.5 million metric tons of water vapor per second, with total moisture content reaching 25–50 millimeters of precipitable water along its length.

These systems, typically 400–600 km wide and thousands of kilometers long, draw moisture from warm ocean regions and funnel it toward land, where uplift from mountains can release the vapor as intense rainfall or snow.

The largest recorded events, such as those impacting the U.S. West Coast during strong El Niño years, have been measured by satellite and radiosonde data to deliver the equivalent of several days’ worth of Amazon River discharge in airborne form, making them both critical to regional water supply and a major driver of flooding hazards.