Parts of Southern California are under a High Risk (level 4/4) of excessive rainfall through Thursday morning, according to the National Weather Service (NWS) Weather Prediction Center.
The system, fueled by a broad plume of moisture from the Pacific, is expected to bring very heavy rain, creating severe, widespread flash flooding. The NWS warned that “areas that normally do not experience flash flooding will flood,” and that “lives and property are in great danger.”
AccuWeather meteorologists emphasized the severity of the storm. Senior Meteorologist Tyler Roys said, “The downtown Los Angeles area is projected to receive 4–8 inches of rain through this week alone, which is two to three times the entire December historical average rainfall of 2.48 inches.” Chief On-Air Meteorologist Bernie Rayno added, “The heaviest rain for Los Angeles is likely to fall through Wednesday. Driving around L.A. during the height of the storm could be especially dangerous.”
Rainfall rates could reach 2 inches per hour, overwhelming storm drains and turning streets into ponds and rivers. AccuWeather Meteorologist Brandon Buckingham warned, “The fast-moving runoff can pick up rocks, mud, ash and debris, quickly turning into a debris flow that can race downhill with little warning, taking out homes, vehicles, and roads along the way.” Areas recently affected by wildfires—including the January Palisades and Eaton wildfires—are at heightened risk.
Northern and Central California, as well as parts of Southern Nevada, are under a Slight Risk of excessive rainfall, with flash flooding possible in urban areas and mountain regions. Downpours are expected to extend into the high and low deserts, including Las Vegas, through Thursday.
Sierra Nevada Mountains: Feet of snow and hazardous travel
Heavy snow will continue across the Sierra Nevada Mountains, with many ridges and peaks expected to receive 8–12 feet, and some areas possibly up to 15 feet, according to AccuWeather Chief On-Air Meteorologist Bernie Rayno. Snow is expected to reach lower elevations, potentially dropping to 5,000 feet by Christmas.
At Donner Pass, along Interstate 80, Tyler Roys said, “From 2–4 feet of snow is forecast, beginning in earnest Wednesday night and continuing through Christmas Day and into Friday.” Some roads, including parts of I-80, may be temporarily closed. While the snowfall will benefit ski resorts and future water supplies, prolonged heavy snow could strand travelers attempting to reach mountain areas.
Air travel and power threats
Air travel through major California hubs, including Los Angeles, San Francisco, and Sacramento, could face delays and cancellations due to strong winds, reduced visibility, and runway flooding, according to Tyler Roys, AccuWeather Senior Meteorologist.
Wind gusts of 40–60 mph are expected in many areas, capable of knocking down trees and causing power outages. The strongest gusts, reaching 60–80 mph, may occur in the Sierra Nevada, northern and central coasts, and around Mount Shasta, with an AccuWeather Local StormMax of 130 mph reported in the mountains. AccuWeather also noted that thunderstorms, hail, and isolated tornadoes or waterspouts cannot be ruled out in some areas.
Lingering effects later this week
From Friday to Saturday, the storm’s intensity is expected to ease, but cold air and lingering moisture will maintain hazardous conditions. Snow may fall on passes along Interstate 5 and Interstate 15, resulting in slippery travel in Southern California through the weekend.
