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Last Weekend Saw the 2nd Rainiest Day in SF History. What Was the First?

Written by Liz LindqwisterPublished Jan. 03, 2023 • 5:00pm
An aerial view of flooding on Highway 101, on Dec. 31, 2022, in South San Francisco | Tayfun Coskun/Anadolu Agency via Getty Images

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A heavy rainstorm battered the Bay over New Year’s weekend, drenching San Francisco in 5.46 inches of rain on Dec. 31—but it was only the second-highest amount of single-day precipitation in city history. 

The No. 1 rainiest? A very wet day three decades ago retains that title by a hair, with 5.54 inches of precipitation in early November 1994. But the record might not hold for long. A third atmospheric river in only a few weeks is poised to hit the Bay on Wednesday, and this brutal storm is expected to bring record-breaking levels of precipitation once more. 

Pedestrians endure the rain while waiting for the MUNI bus at Mission and 24th streets in San Francisco on Dec. 1, 2022. | Camille Cohen/The Standard

Here’s a by-the-numbers look at how this rainy period compares to those in years’ past. 

Atypical, But Not The Worst 

Extreme rainfall has hit most Northern California regions before, and San Francisco is no exception. 

From July 1, 2022, to Jan. 2, 2023, SF recorded 13.47 inches of precipitation, roughly 54% higher than the normal precipitation level during the same period (8.75 inches). 

This put SF roughly on par with the increase in precipitation seen across the Bay Area during that period. Oakland and San Jose both reported an uptick in rainfall levels from July 2022 to today, with areas around Lake Tahoe taking the brunt of the most recent storm: The storm doused South Lake Tahoe with 16.7 inches of precipitation, a whopping 206% of the region’s normal precipitation level. 

Despite back-to-back deluges in December, San Francisco actually had a relatively dry 2022. The city saw only 13 total inches of rain this past year, placing it well below the all-time yearly record of 38.34 inches in 1983. 

The calendar year was dry, but its final weeks were not. Two atmospheric rivers brought December’s rainfall total to 9.66 inches, making it the third-wettest December on record.

The city usually expects high levels of precipitation from January through March, but instead had a very dry early winter season and summer. Following a sunny (and hot) summer, rainfall levels picked back up in September, outpacing expected monthly precipitation levels before skyrocketing in December. 

One result of this uneven—and unusual—rain season? A similarly uncommon fire season. 

Unseasonably high precipitation in September helped quench an already tame summer fire season, helping quickly extinguish large blazes like the Mosquito Fire. On the other hand, the relatively low rainfall levels in early 2022 may have contributed to the fire season’s unusually early start, in which numerous wintertime blazes cropped up in Northern California.  

“The fires that we saw in 2022 start in January, February [happened] because we had an incredibly dry year,” said Capt. Robert Foxworthy, a public information officer at CalFire. “Very low rain levels made some of those conditions more possible for the larger fires to burn.”

Looking ahead, the ongoing slew of rainstorms may help dampen dry brush on California’s forest floors, potentially preparing the state for an easier fire season. 

When SF Was Last This Rainy

The latest rainstorms might jog the memories of San Franciscans who experienced the last record-breaking precipitation levels. The rainiest day in SF history fell on Nov. 5, 1994, bringing just .08 inches more rain than we saw on New Year’s Eve. 

Subsequent flooding from the 1994 storm caused traffic jams and highway accidents, just as we saw following the recent New Year’s Eve storm. In 1994, locals reported tractor-trailers overturned on the Bay Bridge, crashed tankers spilling vats of vegetable oil and roughly 600 accidents across the rainy weekend—80% above normal levels. 

“They’re playing bumper cars out there,” Ray Kafer, then a CalTrans superintendent, told the San Francisco Examiner in November 1994. Other health officials reported numerous rain-related accidents and injuries, following over 50 separate reports of highway flooding.  

Sound familiar? 

Flooding shut down highways across SF this past weekend, and more parts of the region are expected to see traffic jams and road closures. Many communities went without power after the first 2022 storm, and meteorologists warn that the upcoming squall will be catastrophic and potentially life-threatening—especially for unhoused individuals across the city.

Rain floods streets in the Mission on Dec. 31, 2022. | Courtesy El Tapa Taqueria on 18th and Folsom

NOAA Bay Area has not yet responded to The Standard’s request for comment. 

Want to prepare for tomorrow? Check out The Standard’s guide to Wednesday’s storm here

English

Liz Lindqwister can be reached at [email protected]


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