Atmospheric river drenches Los Angeles, triggers widespread flooding

- Torrential rains drenched Southern California on Dec 24, unleashing widespread flash flooding as the authorities urged motorists to stay off roads and residents living downslope of wildfire-scarred foothills and canyons to evacuate.

Downpours measuring 25.4mm or more of rain an hour in some areas were spawned by the region’s latest atmospheric river storm, a vast airborne current of dense moisture siphoned from the Pacific and swept inland over the greater Los Angeles area.

The Christmas Eve storm was expected to persist into Dec 26, posing unsafe driving conditions during what would normally be a busy holiday travel period, according to the US National Weather Service.

“Life-threatening” storm conditions were expected to persist through Christmas Day over Southern California, “where widespread flash flooding is under way”, the weather service said.

A flash-flood warning was posted across much of Los Angeles County until 6pm PST (10am, Singapore time), urging motorists: “Do not attempt to travel unless you are fleeing an area, subject to flooding or under an evacuation order.”

Los Angeles city officials urged residents to heed evacuation orders issued for about 130 homes considered especially vulnerable to mudslides and debris flows in areas where 2024's wildfires ravaged the community of Pacific Palisades.

Dec 24’s heavy rainfall was accompanied by gusty winds that forecasters said were likely to topple trees and power lines. In upper elevations of the Sierra mountains, the storm was expected to dump heavy snow.

NWS meteorologist Ariel Cohen said 100mm to 200mm of rain had fallen in some foothill areas by 9am PST, and the Los Angeles City News Service reported numerous rockslides in the mountains. Forecasts called for more than 300mm of rain falling over some lower-terrain mountain areas by the week’s end.

Forecasters even issued a rare tornado warning for a small portion of east-central Los Angeles County due to heavy thunderstorm activity over the community of Alhambra. REUTERS