Much of California on Monday was preparing to be hit by a powerful winter storm carrying treacherous thunderstorms, high winds and heavy snow in mountain areas.

Jacob Spender, a National Weather Service meteorologist in Sacramento, urged people to take precautions in the coming days, advising them to pack winter safety kits, especially if they plan to travel as winter storm warnings were in place from southwest Oregon to the Southern California border.

Pacific Gas & Electric said in a news release that it was using artificial intelligence and machine-learning enhanced weather models to help determine where to send crews and equipment like power poles and transformers ahead of the storm. The utility company stressed that, unlike most winter storms, the anticipated weather event will “progress in several phases,” with multiple storm systems moving through the region that will likely intensify the risks from wind, rain and snow.

Meanwhile, California's Office of Emergency Services said it is placing fire and rescue personnel and resources in areas most at risk for flooding, mud and debris flows.

Other states on Monday were bracing for different threatening weather events. Residents in parts of eastern Colorado received warnings Monday that they could be in fire danger due to a combination of abnormally high temperatures, gusty winds and dry conditions. The risks are expected to continue further into the week as gusts up to 60 mph (96 kph) are likely to hit the Colorado eastern plains on Tuesday. Parts of Texas, New Mexico, and Kansas were also under red flag warnings.

Back in California, rain had already begun Sunday in the San Francisco Bay Area, sparking officials to warn of potential flood risks.

Forecasters said the western slope of the Sierra Nevada, northern Shasta County — including portions of Interstate 5 — and parts of the state's Coast Range could see up to 8 feet (2.4 meters) of snow before the storm moves through late Wednesday.

The heavy snow, wind and low visibility could also make travel conditions dangerous to near impossible, forecasters added.

“It has seemed ‘spring-like’ for a large part of 2026, but winter is set to show it’s not quite done yet,” the Shasta County Sheriff’s Office said in a social media post urging residents to stay aware of the storm.

To the south, Los Angeles area residents in some neighborhoods scarred by last year’s devastating wildfires were under an evacuation warning through Tuesday because of the potential for mud and debris flows. Los Angeles Mayor Karen Bass said she’s ordered emergency crews and city departments to be ready to respond to any problems.