The woman and her two dogs were killed while walking along a riverbed path just before 9 a.m. local time in Pico Rivera, a city located in southeastern Los Angeles County, the Los Angeles Times reported, citing the police.
"There's a one-in-a-million chance of something like this happening and it happened," L.A. County Sheriff's Sgt. Patrick Morey was quoted as saying by the newspaper.
Pico Rivera officials announced later in a tweet to cancel some outdoor activities, such as field trip and farmers market.
Officials in some Southern California areas urged local residents to stay indoors during the unstable weather. Multiple beaches in Southern California were closed by local authorities due to dangerous weather conditions.