Southern California atmospheric river storm could bring up to a foot of rain and dangerous holiday travel conditions
A powerful atmospheric river headed for Southern California is expected to drop several inches of rainfall, creating the potential for travel challenges primarily on Christmas Eve extending into Christmas, forecasters said Monday, Dec. 22.
The storm is due to arrive during the day Tuesday and will gradually intensify, bringing the heaviest rainfall from Tuesday night into Wednesday, forecasters with the National Weather Service said. A flood watch started in effect Tuesday from 4 p.m. to 10 p.m. Wednesday.
“This will be the first heavy pulse of the atmospheric river,” said Rich Thompson, a meteorologist with NWS’ Oxnard office.
Significant rainfall over Christmas has not happened in the region since 2019, when 1.07 inches of rain were recorded in downtown Los Angeles. The rain record for Christmas Eve was 2.64 inches in 1971, while the most rain to fall on Christmas Day was recorded in 1884 with 3.01 inches, according to the National Weather Service.
A second surge is anticipated on Christmas Day, but it will not be quite as strong, forecasters said. The storm was likely to start tapering off on Saturday.
Los Angeles County valleys and coastal areas could see 4 to 8 inches through Saturday, Thompson said.
Residents in valley and coastal areas in Orange County and the Inland Empire could see upwards of 4 inches by the end of Wednesday, said Lauren Villafane, a meteorologist with NWS’ San Diego office.
The LA County mountains are expected to see between 6 and 12 inches of rainfall, while mountain ranges in Orange County and the Inland Empire could see 5 to 9 inches during the same period, forecasters said. Snow is not likely to fall below 7,500 feet until the weekend, they said, because of a warm air mass and subtropical moisture associated with the atmospheric river, Thompson said. Over the weekend, snow levels may be seen at elevations of 7,000 feet and above.
But the primary concern for forecasters is Christmas Eve, when heavy rainfall could bring mudslides and debris flows to burn scar areas and the possibility of urban flooding, Thompson said.
“The LA River won’t be overflowing, but there will be significant flow, so there could be swift water rescue issues there,” Thompson said. “Pretty much anything you can imagine with bad water things are definitely possible with this storm.”
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