California braces for atmospheric river that could bring life-threatening floods: Live weather updates
Pacific storms dump rain, hail and snow across the West
Californians are bracing for a second round of intense rain and “life-threatening” flooding this weekend.
The National Weather Service for California’s Bay Area has issued a flood watch Saturday through Monday, while the NWS for Los Angeles is forecasting up to 15 inches of rain Saturday through Wednesday. “Life-threatening” flooding is also possible in southern California, forecasters said.
This weekend’s storm could intensify as it approaches the coast, a process called bombogenesis in which a spinning low-pressure system rapidly deepens, according to the Associated Press. The California Governor’s Office of Emergency Services activated its operations centre and positioned personnel and equipment in areas most at risk from the weather.
This weekend’s rain will be the result of a second atmospheric river hitting the West Coast. The first atmospheric river — named the “Pineapple Express,” so called because it originates near Hawai’i in the tropical Pacific — hit the Pacific Northwest and much of California mid-week, causing flash flooding and mudslides throughout the region.
The Pineapple Express system made landfall on Wednesday, causing heavy mountain snow, gusty winds and Rockslides in northern California. In Saratoga, one person was injured after a tree fell on a house, according to the National Weather Service.
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Gustaf Kilander3 February 2024 20:22
WHERE DID THE TERM ATMOSPHERIC RIVER COME FROM?
The name came from research published in the 1990s by scientists Yong Zhu and Reginald E. Newell of the Massachusetts Institute of Technology. Atmospheric rivers are often referred to as ARs.
WHAT HAPPENS WHEN AN ATMOSPHERIC RIVER REACHES LAND?
When the moisture-laden air moves over mountain ranges such as the Sierra Nevada along the California-Nevada line, the water vapor rises and cools, becoming heavy precipitation that falls as rain or snow, according to NOAA.
While traditional cold winter storms out of the north Pacific build the Sierra snowpack, atmospheric rivers tend to be warm. Snow may still fall at the highest elevations but rain usually falls on the snowpack at lower elevations. That can quickly prompt melting, runoff and flooding and decrease the snowpack needed for California’s water supply.
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WHAT HAPPENS WHEN AN ATMOSPHERIC RIVER REACHES LAND?
When the moisture-laden air moves over mountain ranges such as the Sierra Nevada along the California-Nevada line, the water vapor rises and cools, becoming heavy precipitation that falls as rain or snow, according to NOAA.
While traditional cold winter storms out of the north Pacific build the Sierra snowpack, atmospheric rivers tend to be warm. Snow may still fall at the highest elevations but rain usually falls on the snowpack at lower elevations. That can quickly prompt melting, runoff and flooding and decrease the snowpack needed for California’s water supply.
Pineapple Express is a nickname for a strong atmospheric river in the tropical Pacific near Hawaii.
National Weather Service predicts storm to hit between late Saturday and Tuesday
Gustaf Kilander3 February 2024 17:11
PHOTOS: California hit by flooding amid Pineapple Express atmospheric river
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WHAT IS AN ATMOSPHERIC RIVER?
Atmospheric rivers are long and relatively narrow bands of water vapor that form over an ocean and flow through the sky, transporting much of the moisture from the tropics to northern latitudes.
They occur globally but are especially significant on the West Coast of the United States, where they create 30% to 50% of annual precipitation and are vital to water supplies but also can cause storms that produce flooding and mudslides, according to the National Oceanic and Atmospheric Administration.
Formed by winds associated with cyclones, atmospheric rivers typically range from 250 miles to 375 miles (400 to 600 kilometers) in width and move under the influence of other weather.
Many atmospheric river events are weak. But the powerful ones can transport extraordinary amounts of moisture. Studies have shown that they can carry seven to 15 times the average amount of water discharged daily by the Mississippi River, according to the U.S. Geological Survey.
Forty-six atmospheric rivers made landfall on the U.S. West Coast during water year 2023, according to the Scripps Institution of Oceanography’s Center for Western Weather and Water Extremes. Nine were categorized as strong, two were extreme and one was exceptional. California experienced extensive flooding and massive snowfall.
VIDEO: Heavy rain and snow could cause major issues in California this weekend
Heavy rain and snow could cause major issues in California this weekend
Gustaf Kilander3 February 2024 15:07