A “life-threatening” winter storm system began impacting Southern California with flooding rains on Wednesday, prompting evacuation orders in the Los Angeles area and is expected to persist beyond Christmas Day.
Severe Weather Impacts Southern California
Over 38 million residents were under flood watches early Thursday as California Governor Gavin Newsom declared a state of emergency in Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Shasta counties. The declaration addresses threats posed by a series of atmospheric rivers, intense rainfall, and strong winds impacting already saturated soils.
The National Weather Service (NWS) warned the extreme weather would continue through Friday, shutting down roads across the region and triggering evacuations in San Bernardino County due to flash floods and mud and debris flows. A “rare High Risk of Excessive Rainfall” remained in effect through Christmas Day over Southern California, including the Los Angeles metropolitan area.
Flash flood warnings were in effect Wednesday night for Goffs, San Bernardino County, and Los Angeles County’s Antelope Valley, with flood watches extending to the rest of the Los Angeles and San Francisco Bay areas through Friday. The NWS reported “widespread flash flooding” occurring in Southern California amid rainfall rates of 0.5 to 1 inch per hour on Wednesday, marking the heaviest rains of Christmas Eve in the LA Basin.
The first powerful storm brought up to 10 inches of rain to the mountains and up to 5 inches elsewhere, with wind gusts reaching 80 mph, and was moving east out of LA County Wednesday evening. However, lingering showers remained possible. In Antelope Valley, a flood warning remained in effect despite the rain ending, due to ongoing significant flooding.
A second storm system is forecast to bring more showers and possible thunderstorms for most of Christmas Day. While the San Francisco Bay area experienced a brief respite, the NWS noted “strong and damaging winds” would return overnight and continue through Thursday.
Burn scars from recent wildfires – including the Airport, Bridge, Line, Palisades, and Eaton Fires – face an increased threat of mudslides and debris flows. The NWS also warned of dangerous rock and mud slides across Southern California, beyond the risk of flash flooding. Widespread power outages and tree damage were anticipated due to strong winds and saturated soils.
The NWS indicated that areas adjacent to the High Risk zone, including Northern and Central California, and Southern Nevada, could also experience scattered instances of flash flooding through Thursday morning. Snowfall in the Sierra Nevada mountains is expected to reach several feet, making travel over passes impossible this week.
Frequently Asked Questions
What is an atmospheric river?
Atmospheric rivers are narrow currents of moisture-laden air that can transport vast amounts of water vapor thousands of miles, according to the source.
What counties are under a state of emergency?
LA, Orange, Riverside, San Bernardino, San Diego, and Shasta counties are currently under a state of emergency, as proclaimed by Governor Newsom.
What is the current threat level?
A “rare High Risk of Excessive Rainfall” is in effect through Christmas Day over Southern California, including the LA metropolitan area, with “life-threatening atmospheric river conditions” expected to continue.
As conditions evolve, will residents heed warnings and prepare for continued impacts from this powerful storm system?
