Around two weeks after winter storms brought blizzard warnings and feet of snow to parts of California, warm rains are forecast that could cause flooding, officials said.

“It’s going to melt the snow, and on top of that we have warm water on top of the snow,” Fresno County Emergency Services Director Terri Mejorado said at a Wednesday news conference.

Downtown Fresno is forecast to get 3 inches of rain from Thursday evening to Saturday morning, but warm rain and warm temperatures will also melt snow at lower mountain elevations, she said, causing streams to rapidly grow.

The Fresno County Sheriff’s Office on Tuesday issued evacuation warnings for the foothills and mountains, and told people to be ready to leave.

An “atmospheric river” was expected to impact the western U.S. starting Thursday, according to the National Weather Service.

Winter storm warnings starting Thursday were issued for a swath of California that included the Sierra Nevada. Flood watches will be in place in other regions, including in Fresno and the Sacramento Valley, into Sunday.

Sequoia and Kings Canyon National Parks, which are adjacent to each other in the Sierra Nevada, are closing their entrances due to the weather. Heavy rain is forecast for elevations with 12 feet of snow on the ground, the National Park Service said.

“There is major potential for flooding and serious road and infrastructure damage, in the parks as well as the surrounding communities,” the park service said in a statement.

Forecasters in the San Francisco Bay Area warned of a risk of considerable river flooding from the Santa Cruz Mountains and south to Monterey County.

“Preparations should be completed by the end of the day today,” the weather service said Wednesday.

Further south and closer to the coast, Santa Barbara and San Luis Obispo counties could get 4 inches of rain, according to the weather service in Oxnard. Parts of the San Luis Obispo coast and foothills could get up to 8 inches, it said.

In late February, a powerful winter storm brought blizzard conditions and feet of snow Southern California mountains, including around 7 feet to parts of the San Bernardino Mountains northeast Los Angeles.

The heavy snow isolated some communities and trapped some residents in their homes. Wrightwood, a community of 4,700, got around 50 inches of snow, or a little more than 4 feet, according to the weather service.

Mountain highways began to reopen this week after being closed for more than 10 days.