The state of California has found itself in the grips of one of the most destructive storms in its history, with unprecedented levels of rainfall causing hazardous flooding, hundreds of mudslides and wholesale blackouts.

At least three people have been killed by falling trees, in winds that at times have been of hurricane force, in a storm powered by an atmospheric river, dragging in moisture from the Pacific.

It is understood that a remarkable six months worth of rain fell on Los Angeles in just 48 hours, according to the National Weather Service (NWS). Within that period a state-wide record was set, with an astonishing 12 inches recorded to have fallen on Monday 5 February, beating a 123-year-old record, set back in 1901.

LA averages 14.25 inches of rain for an entire year, yet barely a month into 2024 the city has recorded nearly 11 inches already. According to the UCLA Institute of the Environment and Sustainability these figures represent a one-in-1,000-year rainfall event for the region.

Over 152,000 Californians were left without power, and more than 300 mudslides have been reported to emergency services in LA alone. A staggering 38 million people were under flood alerts throughout the state over the course of the storm.

A short period of respite will be followed by a further storm system, which although expected to be weaker, will still carry with it several additional inches of rain and consequently the threat of more floods in southern California.

What is an atmospheric river?

An “atmospheric river” is an effect, or a phenomenon in which water evaporates into the air and is carried along by the wind, forming long currents, which flow in the sky in a similar way to which rivers flow on land.

These can stretch up to 1,000 miles in length and can be as much as 350 miles wide. It was one of the most famous of these – The Pineapple Express – which saturated the state just a few days earlier.

It takes its tropical name from its origins in Hawaii, with a ribbon of water vapour that rolls across the ocean and if lifted by a front, condenses and then pounds the west coast of the US and Canada. California took the brunt and it was followed at the weekend by a second such “atmospheric river” which slammed into the state, wreaking havoc.

Storm claims three lives

Three men have sadly lost their lives as a consequence of tree falls. One occurred when a tree crashed onto a home in Boulder Creek, a community in the Santa Cruz mountains, close to San Jose. Authorities found the homeowner had suffered terrible injuries and was pronounced deceased at the scene.

Another elderly man was struck by a redwood tree in his backyard, in the north of the state.

State of emergency

Evacuations have been necessary in many of the more hilly neighbourhoods in the south, including in LA, with flash floods resulting from the deluge. The record-breaking rainfall has led the governor to declare a state of emergency in eight counties.

Red alert for flash floods

At the weekend 16 residents were forced from their Hollywood Hills homes after mudslides flowed through houses, knocking buildings off their foundations and rupturing gas lines. Witnesses even reported seeing pianos and refrigerators flowing through streets, amongst all the debris.

The entire Los Angeles Basin is on alert for potentially life-threatening flash flooding, with Santa Monica, West Hollywood, Malibu and Beverly Hills thought to be at serious risk.

Storm on the move

The situation is likely to continue for some time yet and flood watches are now in effect throughout portions of southern Arizona and southern Nevada, as the stormy weather crosses into neighbouring states.