What is an atmospheric river?
You may have seen the phrase “atmospheric river” thrown around a lot, but what does it really mean?
The term "atmospheric river" is a term first used in the 1990s to describe a plume of tropical moisture in the atmosphere that can result in heavy rainfall or snowfall.
Use of the term is most common along the West Coast of the United States, but the setup can occur anywhere that persistent winds can transport moisture from the tropics to a mid-latitude location.
Impacts from an atmospheric river can range from beneficial rainfall in drought-stricken areas to significant travel disruptions, flooding, mudslides and excessive snowfall.
During an Atmospheric River, narrow columns of tropical moisture cause enhanced rain and snow for the western U.S.
Atmospheric rivers essentially act like rivers in the sky and can carry the same amount of water as the mouth of the Mississippi River, according to the National Weather Service.
However, not all atmospheric rivers are created equal.
At times, this high-speed conveyor belt of water may act like a giant fire hose. A foot of rain and disastrous flooding may occur a narrow swath, when the system stalls.
When the atmospheric river gradually shifts its position or is not so intense, light to moderate rainfall may be sprayed over a broad area.
Rounds of strong winds may also accompany an atmospheric river.
During an Atmospheric River, rainfall intensifies into narrow bands at the coast and lift along mountains aids in heavier rain and snow.
A more specific version of an atmospheric river is a setup sometimes referred to as a "pineapple express."
In this case, a plume of tropical moisture extends from near Hawaii to California or anywhere along the west coast of North America, according to AccuWeather Senior Meteorologist Ken Clark.
"The term pineapple express was used before the term atmospheric river became popular," Clark said.
An extreme pineapple express setup may bring drought-busting rain, tremendous flooding and mudslides to lower elevations of California, including desert areas. Yards of snow may pile up in the Sierra Nevada, and travel over the passes may grind to a halt.
Atmospheric rivers can also wreak havoc along the U.S. East Coast. For example, disastrous flooding was sparked in South Carolina when Hurricane Joaquin churned off the coast in October 2015.
An aerial view of floodwaters inundating farmland in the reemerging Tulare Lake, in California’s Central Valley, on April 26, 2023 near Corcoran, California. (Photo by Mario Tama/Getty Images)
Even though the core of Joaquin remained well offshore, upper-level winds transported a steady plume of moisture, like a river in the sky, from the tropical system to a non-tropical system over the interior Southeastern states.
In an aerial view, residents are seen using a snow blower to clear snow from the room of a home on March 20, 2023 in Twin Bridges, California. (Photo by Justin Sullivan/Getty Images)
