By Meteorologists Mary Gilbert, Chris Dolce
(CNN) — A major storm is gearing up to deliver months’ worth of rain and powerful winds to Southern California — the most potent in a slew of atmospheric river-fueled storms aiming for the region this week.
It’s coming hot on the heels of a storm that killed at least one person and brought intense flooding to Northern California over the weekend.
The new storm was powering up out over the Pacific Ocean early Tuesday morning. It will start to slam the entire California coast from north to south with rain and wind late Tuesday evening.
Torrential rain will get underway in Southern California very early Wednesday morning and continue through the evening.
A Level 4 of 4 “high” risk of flooding rain is in place for the region Wednesday, including nearly 6 million people in portions of Los Angeles, San Bernardino, Ventura and Santa Barbara counties, according to the Weather Prediction Center.
These high risk flooding events are incredibly significant: High risks are issued on fewer than 4% of days per year on average, but are responsible for more than 80% of all flood-related damage and 36% of all flood-related deaths, WPC research shows.
Wednesday’s high risk is Southern California’s first since February 5, 2024, when disastrous flooding killed at least two people and triggered more than 100 mudslides.
“Widespread and significant urban flooding will be likely along with rock/mudslides and debris flows,” the National Weather Service in Los Angeles warned early Tuesday morning, noting these threats are not just confined to burned areas.
“THIS IS A VERY DANGEROUS HOLIDAY STORM,” the NWS continued. “ANYONE TRAVELING ON CHRISTMAS EVE OR CHRISTMAS DAY WILL NEED TO EXERCISE EXTREME CAUTION.”
California Gov. Gavin Newsom mobilized state resources ahead of the holiday week storm, with agencies pre-positioning crews and equipment, the governor’s press office said.
Rainfall rates could exceed 1 inch per hour at times in the earliest hours of Wednesday morning, especially in the Santa Barbara and Los Angeles county mountains. That’s more than enough to trigger dangerous flash flooding and potentially mudslides.
Life-threatening debris flows are possible on recent burn scars, including from January’s Eaton and Palisades fires, that could be pounded with those torrential rainfall rates. The scorched ground of these scars repels water instead of absorbing it, quickly turning rain into a surge of floodwater that pulls mud and debris with it.
Los Angeles County on Monday announced evacuation orders and warnings for areas in and around burn scars in the greater Los Angeles area, including the Eaton and Palisades fire zones. The deadly blazes were two of California’s most destructive fires in history and burned a combined 16,246 structures, according to CalFire.
The orders are for 383 properties that sheriff’s deputies are directly reaching out to, including going door-to-door, the county Office of Emergency Management said Monday. These eva