California is staring down a round of storms that will bring intermittent rain and snow across the state over the next 10 days, and, with the wet season more than two-thirds over, state water managers are watching the forecast closely, hoping these systems will deliver enough precipitation to offset a deficit in some places that have faced dangerously low levels of precipitation this winter.
A storm pushed onshore on Wednesday, and the chance for rain and snow is expected to persist into early Friday. While this system is weak, forecasters were watching it closely in Southern California, where a slight chance of thunderstorms could bring heavy rain to areas of Los Angeles County that recently burned in wildfires partly fueled by how little precipitation had fallen in Southern California in the months before.
The weekend is forecast to be mostly dry before a second storm arrives as early as Sunday and a third, potentially the strongest and wettest, sweeps the state next week.
California’s annual precipitation, most of which comes during the winter months, is monitored by water managers, farmers, ranchers, Native American tribes, anglers and conservationists. One closely watched metric is the overall snowpack in the Sierra Nevada, a crucial source of water for the state, and it could potentially end the season at normal or above-normal level for the third year in a row if there is a string of monster storms in March. The last time that happened was during the winters of 1998 to 2000, and before that from 1978 to 1980.
When the Sierra snowpack melts in spring, it replenishes reservoirs and underground aquifers through the dry summer, and bolsters the water supply in seasons to come, especially dry ones. The snowpack was 83 percent of its historical average as of Tuesday, with the northern section at 100 percent, the central at 76 and the southern at 75.
“Here at the snow lab, and I think in most of the water world, we’re waiting with bated breath,” said Andrew Schwartz, the lead scientist at the Central Sierra Snow Lab at the University of California, Berkeley. “Are we going to get that third year in a row, or are we going to, so to speak, peter out and end up below average?”
Mr. Schwartz, who tracks snowfall totals at the lab on Donner Pass off Highway 80 in the Central Sierra, thinks these storms are unlikely to bring enough precipitation to bump the season up to normal, but he said it could happen if what meteorologists call the “storm door” — conditions that make rainfall more likely — remains open through the end of the month.
Even if the season ends with a below-normal snowpack, the state is still in good shape in the short term. Nearly all the big reservoirs are above historical averages because the past two winters were wet.
Throughout this winter, Northern California has trended significantly wetter than Southern California. A series of storms moving across the state in February pulled Southern California out of record-dry territory and ended the dire wildfire risk, which had helped fuel the devastating Palisades and Eaton fires in January. But it didn’t bring enough rain and snow to make up for an exceptionally dry start to the wet season.
Flash Flood Risks in Southern California
The storm that arrived on Wednesday should further help Southern California catch up. While it will bring rain across a large portion of the state, the storm was focused over Southern California, with the heaviest rain likely on Thursday. In Los Angeles County where wildfires tore through the landscape in January, there’s a marginal risk thunderstorms could bring heavy rain that sets off debris flows in burn scars.
“I think the main concern is with this storm is coming some cold air aloft which will destabilize the atmosphere and potentially lead to thunderstorms and rainfall rates that will exceed flash flood thresholds,” said Chad Hecht, a meteorologist with the Center for Western Weather and Water Extremes at the University of California, San Diego.
The Weather Prediction Center warned of flash flooding between Ventura and San Diego Counties and across a portion of the southern Central Valley.
Another storm is likely to arrive as early as Sunday, and the third on Wednesday.
Mr. Hecht said there was a lot of uncertainty in the forecast for the third storm, but preliminary predictions suggest it could be a strong system that brings rain across the state and especially to Northern California.
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