The first in a possible wave of wet storms is expected to hit California this week and extend into next week, bringing significant rainfall that could cause some localized flooding, especially in the state’s most northern and southern coastal corners.
Just a week after areas of downtown San Diego were hit by dangerous flash flooding from a historic deluge of rain — inundating homes and highways — forecasters say the area should be prepared for similar conditions Thursday.
“There’s definitely a chance for heavy rain as well as thunderstorms, and that means we do have a risk of flooding on Thursday,” said Brandt Maxwell, a National Weather Service meteorologist in San Diego. “It would be difficult to get a repeat performance of what happened last Monday, but we can’t rule it out.”
With the storm still a few days out, Maxwell said it’s still hard to pinpoint exactly where most of the rain will fall, and how fast. But it’s possible that coastal regions in both Orange and San Diego counties could get one inch of rain within an hour — well above amounts that can prompt flash flooding, he said. But such high rates are expected to be short-lived, with rain totals likely remaining under 2 inches Thursday for much of Southern California.
No flood advisories have yet been issued in the state, but weather officials said it’s likely they will come as the storm moves closer.
As of Monday morning, California’s northwestern corner has the highest probability for some flooding, including around Eureka, Fort Bragg and Redding, where precipitation could begin as early as Tuesday, according to the latest forecasts. But coastal areas across Northern California and the Bay Area are expected to see significant rain, primarily on Wednesday. In the North Bay and San Francisco’s coastal regions, forecasters are warning of the possibility for “shallow landslides and roadway flooding” Wednesday, as well as strong winds.
As the storm moves across the state, the Sierra are also expected to record significant snowfall, and the Southern California mountains above 5,000 feet could get anywhere from a few inches to more than a foot in higher elevations.
Moderate rainfall will reach Central California and Los Angeles County, but no significant flooding is expected for the region, said Lisa Phillips, a National Weather Service meteorologist in Oxnard.
“We’ll maybe see some flooding on roads, minor creek flooding,” Phillips said, “but [we’re] not expecting a flood watch.”
And while forecasters warn this week’s storm is likely the first in a possible string of moisture-heavy storms, there have been no projections for any kind of statewide “megaflood” — as has been rumored in some corners of the internet.
“There is not currently any indication whatsoever of an extremely severe, statewide, catastrophic flood event, resulting from a multi-week sequence of storms,” said Daniel Swain, a UCLA climate scientist, in a Friday webinar. That phenomenon, dubbed the ARkStorm Scenario, has been projected as a 1-in-a-1,000-year megastorm event that would cause massive flooding, as devastating as the Great Flood of 1862.
Researchers in 2022 found that due to the worsening effects of climate change, such a massive storm is projected to become more frequent and intense, with a 2% chance of occurring in any given year, as opposed to a 1% likelihood pre-global warming.
“It is a real thing but it is not something that is headed for California imminently,” Swain said. “The odds of it happening this year remain very low, and the odds of it happening in the next two weeks are close to zero.”
Even still, this week’s storm, which is expected to be part of an ongoing weather pattern, is what Swain called a “potentially high-impact storm pattern.” The forecast of the system falls in line with the typical El Niño pattern, fueled by a warm atmospheric river moving along a strong Pacific jet stream.
A weaker, yet still wet, system is forecast to bring colder temperatures to Southern California on Friday, with some showers likely, Phillips said. And then another storm is expected by Monday.
“Early next week, we could get a pretty substantial storm system — right now it looks slower moving, so the rain could last longer,” Maxwell said. “It could be quite a wet February, at least a wet start.”