A first-ever tornado warning was issued for San Francisco County early Saturday as thunderstorms and wind gusts of up to 60 mph swept through the region, officials said.
“Take shelter now in a basement or an interior room on the lowest floor of a sturdy building,” a National Weather Service advisory warned on social media. Parts of San Mateo County were also included in the warning.
More than 1 million people were under the brief warning, which went out at 5:51 a.m. and was lifted by 6:15 a.m., said Lamont Bain, a meteorologist with the National Weather Service Bay Area.
The advisory was the first time the agency had ever issued a tornado warning for San Francisco County, he said. San Mateo County was last issued a tornado warning on March 18, 2011.
“It’s certainly unusual. We don’t see the ingredients come together all the time for tornadoes,” Bain said.
In addition to moisture, “you need the combination of lift, you need some instability and you need some wind shear. We saw all of those things come together for a brief period of time this morning.”
He said the tornado alert was “a good reminder for people to always have multiple means” to receive weather and warning information. That includes signing up for text alerts, checking news reports and tuning in to weather radio.
Rain showers are forecast for the rest of the day in San Francisco, with wind gusts of 30 to 35 miles per hour through at least noon. The rain is expected to end tonight, with dry conditions on Sunday before another dose of rain on Monday.