Forecasters are increasingly concerned about the possibility of flooding and structural damage as another atmospheric river storm is set to hit California this week, bringing warm rains on top of the state’s near-record snowpack.
Most of the warm storm is expected to hit northern and central California Thursday night and into Friday, but southern California will also feel some effects.
“Friday is pretty much the main day, that’s going to be a flop,” said Mike Wofford, a meteorologist with the National Weather Service in Oxnard. “That could pose some issues at higher elevations where there’s a lot of snow and rain on top.”
Up to 8 inches of rain is possible in the coastal foothills from north of Morro Bay, while the rest of San Luis Obispo and Santa Barbara counties could see up to 4 inches. In Ventura County, up to 2 inches of rain is possible, while the Los Angeles metropolitan area could receive up to 1.5 inches, Wofford said.
Temperatures along the coasts and valleys of Ventura and Los Angeles counties will be mostly in the 60s and 60s, with a chance of 70 degrees in the warmer valley locations.
As the warm rain melts the snow, it could trigger runoff that swells small streams and rivers and causes localized flooding, the weather service said. The Sisquoc and Salinas rivers could reach the stage where they will need to be monitored for possible flooding in low-lying areas.
Most of the storm “should start to subside by Friday night, with some rain remaining early Saturday” in and around Los Angeles, Wofford said. “Most of the weekend at this point looks dry.”
The incoming storm is building as a northern pressure ridge meets subtropical moisture rising from Hawaii. Such systems are sometimes referred to as Pineapple Express and have been known to drop heavy precipitation.
It arrives in the middle of an already exceptionally wet winter in California. A series of nine atmospheric river storms swept through the state in early January, causing widespread flooding and contributing to nearly two dozen deaths.
In recent weeks, powerful winter storms have dumped piles of snow across the state, including some elevations as low as 1,000 feet. The Department of Water Resources’ third snow survey of the season, conducted Friday, found snowpack across the state to be 190% of normal, approaching the all-time record set in the winter of 1982-83.
Of particular concern are the mountains of San Bernardino County, where some residents still remain snowbound after historic blizzard conditions dumped more than 100 inches of fresh powder on the area.
Officials warn that the rain could increase the weight of snow on the structures, which could lead to roof collapse or other problems. Residents and authorities have already reported several roof collapses due to snow accumulation, including a grocery store providing critical supplies at Crestline last week.
The California Department of Transportation plans to send teams from the Sacramento area to conduct avalanche inspections along Highway 18 in the San Bernardino County Mountains on Wednesday, the Orange County Record reported. avalanches have has already been reported at high elevations around Mount Baldy in the nearby San Gabriel Mountains.
Fortunately, rain forecasts for the area are trending downward, according to Samantha Connolly, a meteorologist with the National Weather Service in San Diego, which covers the San Bernardino area. The mountains there could see anywhere from a half inch to 1 inch of rain, with most of it falling overnight Friday and into Saturday.
“Snow levels are going to be very, very high, usually around 9,000 feet, so it will all turn to rain,” Connolly said. “But it’s not looking particularly heavy at any point, and it looks more like a light to moderate type of rain.”
“There could be some minor flows through the roads that have been plowed up, but because the snow pack is so deep and the rain is not as heavy, hopefully it should be able to absorb it,” he added.
Although the rest of the weekend should be dry, the relief may be short-lived as another storm system could head into California next week.
Wofford said the storm will likely reach Southern California on Tuesday morning and begin to abate on Wednesday, though it could last for a second day.
Rain totals are expected to be fairly similar to the first system, he said, though the forecast may change.
