An unseasonably cold storm diving southward through California is expected to bring some snow to the Sierra Nevada and showers, thunderstorms and winds elsewhere, reports the Associated Press.
According to the National Weather Service, there's about a 20 percent chance of rain through the day.
"The real activity will probably be a little bit later tonight into Friday morning," Stewart Seto with the NWS told KPCC. "The chances of precipitation go up to 50 percent, and we'll have a slight chance of thunderstorms with that."
Seto said May usually doesn't see more than a quarter of an inch or so of rain, "but the thing unusual about this one is it's very cold."
Some areas may not see any rainfall, but localized areas could get up to a half inch, potentially producing minor mud and debris flows in wildfire burn areas, reports the AP.
Glendora on the foothills of the San Gabriel Mountains east of Los Angeles has raised its alert level to yellow for residents below a January 2014 wildfire scare, requiring them to keep roads clear of obstructions.
Glendora City Manager Chris Jeffers told KPCC the city would be providing extra sand bags for pickup at their yard.
"We'll have extra police patrols up in the area just to have better eyes and ears during the dark hours just to see what's happening," Jeffers said.
Winter weather advisories are up in the Sierra, where Yosemite National Park has temporarily closed Tioga Road and Glacier Point Road due to snow and ice.
This story has been updated.