Atmospheric rivers are the largest “rivers” of fresh water on Earth

While atmospheric rivers are pretty different from rivers of liquid water down on the ground, they transport water vapor at a rate equal to 7–15 times the average daily discharge of the Mississippi River. They can be hundreds or thousands of miles long, and up to 300 miles wide.

Atmospheric rivers are always flowing somewhere on Earth. At any given time, 90% of the water vapor moving toward the poles is concentrated in about 4 to 5 atmospheric rivers across the globe. 

Atmospheric River plumes over the Pacific in January 2012:

Forecast rainfall by Friday morning, March 17, 2023