California Storm Produces '1 in 1,000-Year' Rainfall Event

California has been hit by a deadly storm that has caused a "1,000-year flood," according to weather experts.

An atmospheric river unleashed extreme rainfall and high winds on the West Coast state across the weekend and on Monday, knocking out power for hundreds of thousands of homes and killing at least one person. Flooding was widespread, with mudslides ripping through multiple areas, forcing emergency services to attend to homes in hillside communities across California.

According to the @US_Stormwatch X, formerly Twitter, account, the storm is a one in 1,000 year rainfall event. "A truly unprecedented storm in modern history for the region as an atmospheric river stalls over the region," it said.

According to the United States Geological Survey (USGS), the term 1,000-year flood "means that, statistically speaking, a flood of that magnitude (or greater) has a 1 in 1,000 chance of occurring in any given year. In terms of probability, the 1,000-year flood has a 0.1 percent chance of happening in any given year."

Newsweek has contacted the USGS via email for comment.

The National Weather Service (NWS) agreed that the storm is historic. "We're talking about one of the wettest storm systems to impact the greater Los Angeles area," Ariel Cohen, the chief NWS meteorologist in Los Angeles, told reporters in a news conference, according to Reuters. "Going back to the 1870s, this is one of the top three."

The NWS said the heaviest rainfall so far has been in Bel Air, LA County, with 11.81 inches falling over the last three days. The average yearly rainfall for Los Angeles as a whole is 18.67 inches, according to World Climate.

The identity of a man in Sacramento county who died after a tree fell on him was confirmed as 41-year-old Chad Ensey, according to NBC News. There were reports of two other deaths that Newsweek has been unable to confirm at this time.

The Los Angeles Fire Department said it had conducted numerous rescues during the course of the storm. One man was saved via helicopter after he jumped into fast-flowing water attempting to save his dog. One report of a child being lost in an undisclosed river was also reported to the fire department, which has confirmed that no child had been found as of Monday, February 6.

More than 100 flooding incidents have been reported, according to the LAFD chief, Kristin M. Crowley.

Mudslides have been reported in hillside communities in southern California. Footage obtained by CBS News showed two mudslides tearing through homes in the San Fernando Valley on Sunday evening. Two homes were reportedly knocked off their foundations, with nine in total evacuated in the affected area.

The office of Governor Gavin Newsom said California residents should "pay attention" to emergency orders and brace for "potentially life threatening impacts". Los Angeles Mayor Karen Bass declared a local state of emergency for the city on Monday.