Rare tornado warning issued amid powerful California storm

U.S. weather authorities issued and later lifted a tornado warning in parts of California on Friday, highlighting unusually unstable atmospheric conditions as powerful storms continued to bring flooding, high surf and heavy snow across the state.

The storm system, driven by an atmospheric river, has caused at least four deaths and widespread damage since last weekend, officials said.

The U.S. National Weather Service (NWS) Forecast Office in San Francisco said a Flood Watch was extended through 10 p.m. on Friday (0600 GMT Saturday) for parts of the Bay Area and Central Coast, warning of rapid rises in creeks and localized flooding. A High Surf Advisory was also in effect through 10 p.m. on Friday, with breaking waves up to about 7.6 meters.

Meanwhile, Southern California recorded unusually heavy rainfall. Downtown Los Angeles received 6.6 centimeters of rain from December 24 through midday of December 25, making it the wettest Christmas Eve and Christmas Day since 1971, according to NWS.

In the Sierra Nevada, the storm dumped massive snowfall, with the University of California, Berkeley's Central Sierra Snow Lab reporting about 60 centimeters of snow within 24 hours.

Strong winds caused notable damage at the historic Lick Observatory near San Jose, where gusts tore part of a 137-year-old telescope dome from its structure.

Power disruptions remained a significant operational challenge. Pacific Gas and Electric (PG&E) said that ahead of the storm sequence, more than 5,500 frontline coworkers and contractors would be on storm duty.

Weather experts warned that the most serious risks stem from flash flooding, debris flows and mudslides, particularly in Southern California's steep terrain.

Looking beyond California, winter storm warnings and difficult travel conditions extended into nearby high-elevation areas in the broader region, according to NWS offices serving the Sierra and adjacent interior West.