Like in Kerr County in Texas, most California localities don’t use sirens to alert the public about flooding, “because our flooding kind of builds and we can see what is coming in,” state climatologist Michael Anderson said. However, some do, like the Marin County communities of Fairfax, Ross and San Anselmo, which maintain flood horns or sirens that they sound when flooding is imminent. 

California relies heavily on the weather service for messaging about potential flooding from storms. For instance, last December, San Franciscans were startled awake by a blaring weather alert on their phones warning them of a potential tornado.

When it comes to flooding, the weather service issues watches, warnings and advisories. Flash flood warnings also have three different levels, ranging from the base level to catastrophic. Beyond the alerts, the weather service leans on traditional radio broadcasts, local authorities and news outlets to get the word out.

Garcia said the difference between a warning and an advisory is that a warning suggests “there could be trouble,” but an advisory means “the trouble is coming to you.” He recommends that all Bay Area residents sign up for text emergency alerts at alertthebay.org and pay attention to any “action statements” within the message.

“If the action statement says something like get to high ground immediately, that is a cue to take immediate action,” Garcia said. “Whether it’s moving to higher floors, going to the top of a hill, or moving yourself to higher ground.”

Flooding from thunderstorms is possible in California

What distinguishes the Bay Area’s localized flash flooding events from those in Texas is the duration of the atmospheric river, its geographic location and the level of wetness in the system. Atmospheric rivers in California can last for days and arrive in a succession train, while thunderstorms last for a few hours at most.

“Texas can get these systems that consist of thunderstorms that don’t move very much over a period of time, producing an enormous amount of rainfall,” said John Monteverdi, emeritus professor of meteorology at San Francisco State University. “That’s different from the kind of flooding that happens when the Russian River floods, maybe once every two or three years.”

Still, a big flash-flood-producing thunderstorm in California isn’t entirely out of the picture and can occur during the summertime in the Sierra Nevada or the deserts across the southeastern part of the state.

“The kind of thing that happened in Texas could also happen in California,” said Nicholas Pinter, associate director of the UC Davis Center for Watershed Sciences. “Anyone out hiking in confined, rugged topography needs to be aware that we have this risk of flash flooding in California, kind of similar to Texas.”

While the Texas thunderstorm covering a broad geographic area and producing a wall of water is “not typical of California,” the “wettest precipitation events are getting wetter” and in turn elevating flood risk, which is in line with the effects of human-caused climate change on storms in both states, said Noah Diffenbaugh, a climate scientist at Stanford University.