From The National Oceanic And Atmospheric Administration”
https://scijinks.gov/atmospheric-river/
“...Atmospheric rivers are regions of the atmosphere
carrying water vapor from the warm, moist air of tropics
until they drop the water over cooler regions as rain or snow.
They are about 250 miles wide and about 1,000 miles long.
If you hear your meteorologist mention an atmospheric river,
you can expect lots of rain or snow in the forecast.
Atmospheric rivers are fairly common in winter in the Western U.S.
In fact, just a few atmospheric river events each year
cause up to half of the annual precipitation on the West Coast...”
I first heard the term “atmospheric river” in 2023.