Southern California Welcomes Surge of Moisture: Is a Soggy March on the Horizon?

After a lackluster start to the rainy season in Southern California, the region welcomed a surge of moisture Wednesday that forecasters say could be the beginning of a soggy March.

Rain began falling in Los Angeles County on Wednesday afternoon, and showers are expected to continue through early Friday. Next week is expected to deliver even more moisture — potentially an atmospheric river — to Southern California’s parched landscape.

The region endured one of its driest starts to the rainy season in recorded history, which helped fuel one of the most destructive fire seasons ever. But a wet March could help the region delay the return of high fire season, said Robbie Munroe, a meteorologist with the National Weather Service in Oxnard.

“The longer we can have wet weather into the spring, it will usually help us delay when things get a chance to really dry out,” Munroe said.

Ahead of the storm that arrived Wednesday, downtown L.A. had received 5.58 inches of rain since the water year began Oct. 1. That is below the average for this point in the water season, 11.08 inches. The annual average is 14.25 inches.

“We’ve been playing catchup, it feels like, the whole winter after an extremely dry period through January,” Munroe said. “February was still a little below normal, but at least it kind of got us closer to what we might see this time of year.”

Between a tenth of an inch and an inch of rain is expected for the coastal regions during this week’s storm, and between 1 and 2 inches of rain could fall in the foothills and mountains. One to 5 inches of snow could fall in elevations above 4,000 feet, and between 6 and 12 inches could drop at elevations above 6,000 feet, according to the weather service.

The storm is expected to deliver light to moderate cold rain with intermittent dry spells, according to Rose Schoenfeld, a meteorologist with the National Weather Service in Oxnard.

“There is still some range of impacts, but we are much more confident that this storm will be fairly benign, mostly beneficial rain,” Schoenfeld said Wednesday.

The storm is also expected to unleash strong winds in some areas. There’s also a slight potential for thunderstorms, particularly late Wednesday through Thursday, which could deliver heavy downpours along with gusty winds, lightning, small hail and even weak tornadoes. Thunderstorms have a greater chance of occurring in San Luis Obispo and Santa Barbara counties, according to the weather service.

Los Angeles County officials said Wednesday that they were prepared for rain to hit the burn zones. The Palisades and Eaton fire burn scars are of particular concern during rain events because of the risk of debris flows.

Peak rainfall rates could reach between a tenth of an inch and a third of an inch per hour, with rain rates in some areas reaching half an inch per hour. Experts say the risk of mud and debris sliding off burned hillsides rises once rain starts falling at a rate of half an inch per hour.

“There’s a potential for isolated mud flows and some streets could be blocked by mud and debris,” Angela George-Moody, chief deputy director of L.A. County’s Department of Public Works, said during a news conference Wednesday.

George-Moody said crews have assessed all flood control facilities to ensure they’re cleared out and ready to capture any runoff from the storm. She urged homeowners to clear drainage paths on their property and use sandbags to direct runoff and protect structures ahead of the rain.

The burn zones have already seen the effects of wet weather this winter.

Heavy rain last month sent mud and debris surging onto Pacific Coast Highway — sweeping a vehicle into the ocean — and forced the indefinite closure of Topanga Canyon Boulevard between Pacific Coast Highway and Grand View Drive.

This week’s storm is not forecast to be as strong as the one that hit the region last month. But heavier rain could be on the horizon, forecasters say.

After Friday, Southern California is expected to see a few days of dry weather before more rain returns on Monday. That storm system could bring light to moderate rain through Tuesday.

Another storm forecast to arrive the day after that and last through March 13 could potentially bring bands of heavier rain, but exact amounts aren’t yet certain.

There’s a 40% chance of moderate rain amounts —between 1 and 2 inches — with that storm. There’s a 30% chance the storm could bring even more rain than that, between 2 and 4 inches. And there’s a 30% chance it will deliver rain amounts under an inch, according to the weather service.

Schoenfeld said that the “storm does have some signals that indicate that we could end up seeing more of a significant atmospheric river with greater impacts.”

In the meantime, this week’s storm system is also expected to bring fresh powder to California’s mountain ranges.

In Northern California, the weather service issued a winter weather advisory for the northern Sierra Nevada, warning of snow accumulations of 3 to 8 inches at elevations between 4,000 and 5,500 feet — with 10 to 16 inches expected at higher elevations. The advisory, which is in effect through 4 p.m. Thursday, warns that “travel could be difficult at times from slick … conditions, chain controls, and travel delays.”

In Southern California, the weather service issued a winter storm warning for the eastern San Gabriel Mountains. The warning, which is in effect from 7 p.m. Wednesday to 7 a.m. Friday, cautions that travel could be “very difficult to impossible” as snow falls in the area.

The storms could help bolster the state’s snowpack, which has suffered during the warm, dry winter. As of Tuesday, the snowpack — which typically melts to supply nearly a third of the state’s water — was 83% of average for this time of the year.