California weather: Atmospheric river slams West Coast with heavy rain and wind

The atmospheric river is expected to hit California in two parts.

The National Weather Service (NWS) predicts that the first storm will affect the region Thursday.

According to the forecaster the second storm system is expected to reach Southern California sometime on Sunday, beginning a “lengthy storm cycle’’ that could bring widespread rain totals of two to four inches in lower elevations, and possibly twice as much in south-facing mountains.

More than 20 million Californians are under weather alerts.

Earlier on Wednesday, the California Governor’s Office of Emergency Services activated its operations center and positioned personnel and equipment in areas most at risk from the weather as the first of two atmospheric river storms hit the state.

Brian Ferguson, California OES deputy director of crisis communications, characterized the situation as “a significant threat to the safety of Californians” with concerns for impact over 10 to 14 days from the Oregon line to San Diego and from the coast up into the mountains.

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

The “Pineapple Express” — so-called because its long plume of moisture stretched back across the Pacific to near Hawaii — will be followed by an even more powerful storm on Sunday, forecasters said.

The second storm in the series has the potential to be much stronger, said Daniel Swain a climate scientist at the University of California, Los Angeles.

Models suggest it could intensify as it approaches the coast of California, a process called bombogenesis in which a spinning low-pressure system rapidly deepens, Swain said in an online briefing Tuesday. The process is popularly called a “cyclone bomb.”

That scenario would create the potential for a major windstorm for the San Francisco Bay Area and other parts of Northern California as well as heavy but brief rain, Swain said.

The California Governor’s Office of Emergency Services activated its operations center and positioned personnel and equipment in areas most at risk from the weather.

Brian Ferguson, Cal OES deputy director of crisis communications, characterized the situation as “a significant threat to the safety of Californians” with concerns for impact over 10 to 14 days from the Oregon line to San Diego and from the coast up into the mountains.

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

Last winter, California was battered by numerous drought-busting atmospheric rivers that unleashed extensive flooding, big waves that hammered shoreline communities and extraordinary snowfall that crushed buildings. More than 20 people died.

The memory was in mind in Capitola, along Monterey Bay, as Joshua Whitby brought in sandbags and considered boarding up the restaurant Zelda’s on the Beach, where he is kitchen manager.

“There’s absolutely always a little bit of PTSD going on with this just because of how much damage we did take last year,” Whitby said Wednesday.

The first of two back-to-back atmospheric rivers drenched Northern California on Thursday, flooding roads while triggering statewide storm preparations and calls for people to get ready for powerful downpours, heavy snow and damaging winds.

Heavy rain and gusty winds that began hitting the San Francisco Bay Area on Wednesday evening were expected to continue powering down the coast, according to the National Weather Service.

The river of rain “will be taking aim at mostly Southern California” on Thursday, weather service forecaster Bob Oravec said.

The Los Angeles and San Diego areas will be in the bullseye for heavy rain on Thursday, “especially for some of the higher elevations where they tend to get most of the rainfall — or the heaviest rainfall — with these atmospheric river events,” he said.

The weather service issued a flood watch into Friday morning for the Bay Area and the Central Coast because of possible flooding of rivers, streams, some roads and areas scarred by previous wildfires.

Forecasters also said the Central Coast could see waves up to 18 feet high on Thursday and Friday.

Service on San Francisco’s iconic cable cars were halted as a safety precaution, and Pacifica, a coastal city in San Mateo County, saw more than an inch of rain in a single hour.

A massive atmospheric river known as a “Pineapple Express” is barrelling towards the US West Coast, with torrential rain and powerful winds raising the threat of heavy flooding and landslides.

Forecasters warned that up to eight inches of rain expeced in some areas of northern California.

Here’s what you need to know about the approaching storms:

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 called the “Pineapple Express” – predicted to soon hit California – 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.

Prevailing winds cross over warm bands of tropical water vapor 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 vapor and the strongest winds are responsible for extreme rainfall and subsequent flooding. These events can affect the entire west coast of North America, often disrupting travel and damaging property in the process.

The Los Angeles branch of the National Weather Service issued a seven-day summary of the appraoching storms, advising residents to begin preparing.

The forecaster said that the first storm – a “Pineapple Express” lasting Wednesday and Thursday – would see moderate flooding focused on roads.

A more severe second storm, taking place from Sunday to Tuesday or Wednesday next week, would see growing potential for damaging flooding rain, strong winds, and lots of mountain snow.

“Start preparing now. Adjust plans. Grab sandbags. Mountain communities, grab extra supplies in case you are stranded,” NWS LA wrote on X.