Torrential rain has brought flash flooding and landslides to California, closing roads, felling trees and raising avalanche fears, in the latest winter storm to hammer the state. President Joe Biden offered emergency federal assistance over the atmospheric surge, known as a “Pineapple Express”. The National Weather Service (NWS) has warned of a high risk of excessive rainfall throughout the weekend. This is the state’s 10th so-called atmospheric river just this winter. Atmospheric rivers occur when water evaporates into the air and is carried along by the wind, forming long currents that flow in the sky like rivers flow on land. They can lead to severe rain and mountain snow. This system — which began on Thursday — is known as a “Pineapple Express” because it brings warm subtropical moisture across the Pacific from near Hawaii. “Lives and property are in great danger,” the NWS said. “Areas that normally do not experience flash flooding will flood.” Nearly all of California’s 39 million residents were under some type of weather warning as of Friday. The heaviest precipitation is expected to hit central California, while “copious amounts of heavy snow” could make travel dangerous in parts of northern California and the Sierra Nevada mountain range, where mudslides and rockslides are also possible, according to the NWS. As much as 10in of rain in 24 hours could fall in some parts of the state where there is snowpack, meaning the “potential for widespread flooding is considerable”, the NWS said. It urged California residents to steer clear of barricaded and flooded roads. Avalanche danger in the Sierra Nevada Mountains has risen to a level four out of five as rain falls on over 10ft of snow in some regions. “Widespread avalanche activity is expected to occur with heavy loading of the snowpack from rain and high intensity snowfall,” the Sierra Avalanche Center said in its Friday backcountry avalanche forecast. California is still reeling from a series of extreme weather events this month and last. California Governor Gavin Newsom has declared a state of emergency in 34 counties in the state amid one of its wettest winters on record. Nearly 10,000 California residents were under evacuation orders on Friday evening, according to the state’s director of emergency services. Almost 50,000 homes and businesses have lost electricity, according to website PowerOutage.us. At least eight deaths were being investigated as possibly related to the weather, while two deaths have been conclusively tied to the storms. — BBC