Atmospheric rivers: How they increase a storm’s moisture
Columbus and Central Ohio Weather
COLUMBUS, Ohio (WCMH) — The term “atmospheric river” refers to a long plume of water vapor emanating from the subtropics.
An atmospheric river is not a storm, but instead behaves like a fire hose that shifts with the approach of a storm system. The channel of moisture is typically 250 to 375 miles wide and a little more than 2,000 miles long.
Remarkably, an atmospheric river is capable of carrying as much as seven to 15 times the typical amount of water released in a single day through the Mississippi River, according to the U.S. Geological Survey.
Storms arriving from the North Pacific tap the corridor of moisture, which enhances the potential for very heavy rain and mountain snow, as sopping air is lifted thousands of feet, cooling and condensing into precipitation. The supply of water vapor is being aided by evaporation from a pool of anomalously warm water (3 to 4 degrees above normal) in an El Niño pattern.
Moisture slamming into the Pacific Coast Ranges and Sierra Nevada mountains usually unloads copious amounts of low-elevation rain and mountain snow. Rainfall in Central and Southern California in the coming days will total 2 to 6 inches, with locally 8 to 12 inches on the south (upslope) side of the San Gabriel Mountains and the Transverse Ridges than run west-east.
Over the interior West, several feet of snow are expected in the Sierra Nevada, where the snowpack is only about the normal amount, so the heavy snow is welcome.
Atmospheric rivers are not limited to the North Pacific, occuring in other parts of the world where the upper-level winds tap tropical moisture. Surges of water vapor drawn from the Caribbean Sea and North Atlantic contributed to widespread flooding in parts of the Mid-Atlantic and Northeast in mid-July 2023, and again in early January 2024.
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