California atmospheric river: West Coast braces for life-threatening floods

According to the National Oceanic and Atmospheric Adminstration (NOAA), atmospheric rivers are narrow regions in the atmosphere that transport much of the moisture from the tropics to northern latitudes. The weather systems are part of the Earth’s ocean water cycle, and are tied closely to both water supply and flood risks.

A well-known example of a strong atmospheric river is the “Pineapple Express” – which hit California earlier this week – so-called because moisture builds up in the tropical Pacific around Hawaii and can wallop the U.S. and Canada’s West Coasts with heavy rainfall and snow.

A second atmospheric river is set to hit California this weekend.

Prevailing winds cross over warm bands of tropical water vapour to form a “river,” which travels across the Pacific as part of the global conveyor belt. When it reaches the West Coast, the Pineapple Express can dump as much as five inches of rain on California in one day.

According to NOAA, atmospheric rivers come in all shapes and sizes, but those that contain the largest amounts of water vapour and the strongest winds are responsible for extreme rainfall and subsequent flooding. These events can affect the entire West Coast, often disrupting travel and damaging property in the process.

Despite the strong winds and heavy rain in Los Angeles brought on by the Pineapple Express storm, surfers braved the conditions to hit the waves on Thursday morning.

Famous tourist hotspot Venice Beach, which usually sees thousands of people and vendors passing through, was shuttered and quiet, as gusts battered the boardwalk.

Only a handful of thrill-seekers remained, delighting in the waves – which reached up to six feet. Among them was Ian Dell, who described the outing as “a regular Tuesday”.

A giant redwood tree fell on a Saratoga, California home and car on Wednesday, trapping a young girl inside the vehicle. She was transported to the hospital with only minor injuries, NBC Bay Area reported.

Despite the warm, tropical air that the Pineapple Express brought to much of the West Coast this week, the atmospheric river also dumped several inches of snow on the Sierra Nevada Mountains.

The Mammoth Mountain ski resort, pictured below, got 12-14 inches of snowfall Thursday night into Friday, the Associated Press reports.

Stay out of the ocean, Californians.

“An {Ocean Water Quality Rain Advisory} has been declared by @lapublichealth and it is recommended to avoid water contact for at least 72 hours due to elevated bacteria levels,” the Los Angeles County Fire Department said on X.

Officials first announced the advisory on 1 February, as a deluge fell on southern California thanks to the Pineapple Express storm system. Residents should avoid contact through at least Sunday.

Earlier this week, the Pineapple Express system brought several inches of snow to high-elevation areas of California, burying ski resorts in the Sierra Nevada Mountains.

Now, the second storm forecasted to make landfall this weekend will bring even more snow to those regions, forecasters warn.

Experts with the National Weather Service for Los Angeles say Californians should change their plans to avoid mountain travel and that residents of high-elevation areas should stock up on supplies and gas ahead of the storm.

The second atmospheric river will hit Saturday night and bring heavy rain through early next week. The peak of the storm will hit Sunday night through Monday morning, forecasters say.

Thanks to a process called a “cyclone bomb” — or “bombogenesis” — the second storm poised to hit California will be far more intense compared to the mid-week “Pineapple Express,” the Associated Press reports.

Current models of the low-pressure system suggest it will rapidly deepen, bringing a deluge to the state and possibly creating a major windstorm for the Bay Area. National Weather Service forecasters are predicting wind gusts as high as 60 miles per hour near San Fransisco, California on Sunday.

Storm damage will continue to impact some Californians for the next fourteen days, even as storms are projected to end early next week, said Brian Ferguson, deputy director for crisis communications at the California Governor’s Office of Emergency Service.

Mr Ferguson told the Associated Press the storms will pose “a significant threat to the safety of Californians” for up to 14 days, from the Oregon coast down to San Diego, stretching from the coast into the mountains.

“This really is a broad sweep of California that’s going to see threats over the coming week,” Mr Ferguson told the AP.