Northern California is gearing up for its first significant storm of the season as a moisture-rich atmospheric river is forecast to bring rain to the region starting as early as Sunday night, with showers expected to continue into Monday and Tuesday.
Eureka and areas to the north are likely to bear the brunt of this early-season precipitation, with anticipated rainfall totals ranging from 1 to 3 inches. In contrast, the Bay Area is expected to experience only light showers, according to the National Weather Service.
Atmospheric rivers, those narrow channels of moisture originating from the tropical Pacific Ocean, are notorious for delivering substantial rainfall upon reaching land. Although the forthcoming system is expected to be moderately strong, forecasters predict it won’t be exceptionally wet. It will primarily concentrate its effects over southern Oregon and northwest California.
The Pacific Northwest and far NorCal are on track to see a significant atmospheric river dropping widespread rainfall amounts of 1-4 inches early next week.— Colin McCarthy (@US_Stormwatch) September 22, 2023
This will likely bring fire season-ending rainfall from Eureka northward and likely put an end to the wildfires, sending… pic.twitter.com/N41oUaOwhB
“I think you can accurately call this storm an atmospheric river, and it’s actually a pretty strong one,” said James White, a forecaster at the weather service’s Eureka office “It’s not unusual to get one this early, often we’ll get some weak systems, but as a very first system, it’s unusual to get one this strong.”
In California’s northwest corner, including Del Norte, Humboldt, Siskiyou, and Trinity counties, valleys are projected to receive 1.5 to 2 inches of rainfall, with mountainous areas potentially seeing up to 3 inches. Shasta County should expect slightly less rain, with anticipated totals of 0.5 to 1 inch. There may even be a light dusting of snow around Mount Shasta. Further south, sections of Mendocino County could record up to half an inch of rain, while Lake County is set to receive around a half inch in mountainous areas and a tenth of an inch around Clear Lake.
“The timing has been a little uncertain, but most of the models at this point are starting to agree that we’ll start to see rain as early as Sunday evening, with the heaviest rain Sunday afternoon into Monday,” said White.
The storm’s impact is expected to be most significant in the Sacramento Valley and Sierra foothills, primarily on Monday afternoon and evening into Tuesday.
In the northern Sacramento Valley, moderate to heavy passing showers are anticipated. Redding is likely to receive 1 to 1.5 inches of rain, while Red Bluff and Chico could see 0.25 to 0.50 inches. Totals will be lower in the southern parts of the valley, with Sacramento predicted to record only a tenth of an inch.
According to the weather service’s Sacramento office, for the foothills and mountains north of I-80, storm totals will generally range from a third of an inch to 1.5 inches. Unfortunately, the chances for snow in the Sierra Nevada are low.
“It looks like the Sierra and Tahoe are largely going to miss out on this atmospheric river,” said Brian Hurley, a meteorologist with the National Weather Prediction Center.
It’s official – summer is gone and the fall season has officially arrived in NorCal. Bring on the rain!