Storm-weary California endures record-breaking rainfall totals

It's time to break out the record books, sort of. This winter's heavy rains in California broke records for any 22-day time frame between Oct. 1 to Jan. 16.

"This year we are at 17.87 inches, which is among the largest to date," said state climatologist Michael Anderson. But, he said, California has a long way to go to break the record for the wettest year: "The largest water year was 1982-1983 which totaled 42.81 inches."

"Water years" are counted from Oct.1 through Sept. 30 of the following year. 

The state's precipitation is more than 7 inches ahead of typical water years, according to California Water Watch. At this stage of the 2022-2023 water year, large portions of the state have seen double their average precipitation.

The data, from Oregon State University’s PRISM product, is based on the network of real-time precipitation sensors spread throughout California.

For some cities. it wasn't the wettest 22-day period.

"Downtown San Francisco did not see record rainfall in this period (Dec. 26 through Jan. 16) due to even more exceptional rainfall in the Great Flood from December 1861 to January 1862," National Weather Service meteorologist Jeff Lorber said. "Downtown San Francisco is our only site that has records that far back."

San Francisco's total rainfall of 17.64 inches was second to that rainy season more than 160 years ago, when the same time period saw 18.49 inches.

That doesn't mean records weren't broken around the state, Lorber said. Records were toppled for the 22-day period from Dec. 26 through Jan. 16 in areas around Oakland, Napa and Sonoma.

Lorber's calculations put all three locations well above their former records. Downtown Oakland received 18.33 inches, topping the previous high by 8 inches. Napa was nearly 5 inches higher at 15.19 inches, and Sonoma's 15.8 inches beat its previous high of 12.56 inches. 

Rainfall in California from a monthly perspective

December and January rainfall totals have been above average in several parts of the state. The California Department of Water Resources averages data from 19 weather stations spanning the state and generates averages for three regions.

The charts below compare year-to-date monthly averages at these combined stations. December 2022's totals are well above average in all three regions: Northern Sierra 8-station, 6.7 inches above average; San Joaquin, 9.3 inches higher; and Tulare, 4.8 inches higher. 

At a few days past the halfway point, January is already above average.

Central California, the Southern California coastlines and the Sierra Nevada regions are 200% ahead of their average precipitation to date, said David Rizzardo, hydrology section manager for the water resources department. 

“Not surprisingly, these are also the areas where we’ve seen the greatest impacts from flooding: levee breaks, mudslides, inundated highways and heavy snow accumulations from the series of atmospheric rivers that began in late December and persisted into mid-January,” Rizzardo said.

Total accumulated rain in California

When compared with historic water years, 2022-2023 is off to an impressive start in the same regions.

The Tulare and San Joaquin basins are tracking their wettest years in history, with almost half of January remaining.

“The precipitation accumulation in the San Joaquin and Tulare Lake Basin regions are around the same pace as the other two wettest historic years on record (1968-69 and 1982-83)," Rizzardo said.

More records are within reach, though skies appear to be clearing in coming days.

"We are expecting dry weather the next two weeks, and (the total) will fall off the pace from 1983." Anderson said. "We will have to wait for the end of the year to see where we end up in rankings."