A quick-moving atmospheric river, capable of bringing heavy downpours and mountain snow, is expected to drench San Diego County by late Thursday, and it could offer some early clues about the water year.
California’s water year runs from Oct. 1 through Sept. 30. January and February are typically the wettest months. So far this season, a Pacific storm in mid-October brought more than an inch of rain in the mountains and about four-fifths of an inch along the coast.
The incoming atmospheric river, which originated in Alaska, coupled with October’s rainfall, will offer an early moisture boost, said Alex Tardy. He is a former meteorologist with the National Weather Service (NWS) who founded Weather Echo, which provides weather and climate interpretive services.
“When we do get snowpack, and we do get more rain from the few storms we have in the winter, it can help allow that water to not just go into the ground,” he said, “but go into our reservoirs where we really need to have it for storage.”
An early season atmospheric river may be an outlier in an otherwise dry year. According to the National Oceanic and Atmospheric Administration’s Climate Prediction Center, La Niña events, which tend to bring drier conditions for Southern California, are favored to persist this winter. San Diego recorded 5.07 inches of rain during the last water year, which fell short of the annual average of 9.79 inches. The previous water year reached just over 12 inches.
“The overall winter is expected to be drier than normal all the way through March,” said Tardy. “That would mean less storms, less opportunities for rain. So, getting it now, we’ll definitely take it.”
The atmospheric river storm is expected to clear out by midday Friday. Some rain showers after the cold front passes are possible Friday afternoon into early Saturday, according to the NWS. Dave Munyan, a forecaster with the NWS, said there’s a 75% chance that a lot of places along San Diego’s coast will see at least half an inch of rain.
These conditions can significantly help reduce the risk of wildfire, said Julia Kalansky, a climatologist at Scripps Institution of Oceanography.
“There’s been studies done at Scripps Institution of Oceanography that looked at how much rain is needed in the Southern California region to really mitigate wildfire risk and it showed that it was about a third of an inch over three days,” she said.
With rain on the way, the county of San Diego announced Monday that it is providing free sandbags at various fire stations to protect against flooding and runoff. Some stations may have a limited supply. County officials encourage the public to call stations ahead of time.
