Fire officials have issued a mandatory evacuation of 39 homes in Acton, effective this morning, as forecasters predict the most powerful storm of the week will begin today.

The evacuation orders cover 39 homes in Acton in addition to more than 400 others throughout areas burned by the Station Fire in La Cañada Flintridge, La Crescenta and Glendale.

Officials have asked evacuees to be out of their homes by 1 p.m. today.

“We are involved in a race against mother nature,” said Los Angeles County Fire Chief P. Michael Freeman during a Tuesday night news conference. “If she wins the race, there’s no way we can assume firefighters ... can get into your neighborhoods and make rescues.”

Tuesday’s storm dumped nearly an inch of rain on the Santa Clarita Valley, flooding roadways and contributing to several seemingly minor crashes throughout the Santa Clarita Valley.

Meanwhile, fire officials urged Acton residents to take today’s evacuation orders seriously, and said the orders could remain in effect as late as Monday.

The strong storm is expected to hit the Santa Clarita Valley in the early afternoon, dumping 4 to 8 more inches of rain on the Santa Clarita Valley through Thursday night, according to the National Weather Service.

Pending the worst-case scenario, residents would be let back into their homes on Monday, said Chief Neil Tyler of the Los Angeles County Sheriff’s Department.

Flash flood and debris flow warnings remain in effect for areas burned by the Station Fire.

“There’s a lot of moisture still in the air,” said NWS Weather Specialist Bonnie Bartling.

A service report urged travelers not to drive their vehicles through areas where water covers the roadway, as the depth may be too dangerous. Signs were up Tuesday around Sand Canyon Road warning drivers of flooding.

California Highway Patrol officers temporarily closed a lane on Highway 14 after a Los Angeles County Department of Parks and Recreation truck overturned, CHP officials said.

The truck, weighing about 4,500 pounds, overturned on northbound Highway 14 near Placerita Canyon Road at about 12:30 p.m., said CHP Officer Francisco Villalobos.

The truck blocked the carpool lane, which officers closed from about 1:30 p.m. to 2 p.m., officials said.

A man in the truck was able to exit the vehicle and fell into a traffic lane, said Los Angeles County Fire Inspector Matt Levesque.

He was transported to Henry Mayo Newhall Memorial Hospital just before 1 p.m., Levesque said.

Local California Highway Patrol officers responded to 22 collisions on Sunday and 28 collisions on Monday, said CHP Officer Michelle Esposito.

Esposito said the number of collisions that occurred Tuesday was not readily available.

CHP officials started getting more reports of collisions after rain started falling more heavily from noon to about 1:30 p.m.

“The amount of water on the roadway is heavy and people aren’t adjusting their speed accordingly,” Esposito said. “(People should) leave plenty of space between their (vehicles) and the vehicles ahead of them.”

She also said people should be sure their windshield wipers are working and their tire pressures are at the correct levels.

A sheriff’s official reported no major flood hazards on non-highway roads in the afternoon.

“As of right now it has been — thank God, knock on wood — quiet,” said Sgt. Derrick Ballentine.

Two contract workers shoveled mud Tuesday from a sidewalk just off the north-bound Magic Mountain off-ramp of Interstate 5.

“All this is new backfill so when they get rain, the mud washes down,” said Edgar Razo, of Southwest Contractors. “We’re placing sandbags so nothing goes into the street.”

As raindrops splashed against his face, Razo said didn’t enjoy working in the rain.

“But we have no choice,” he said.

Shoppers beneath umbrellas and rain jackets hustled to their cars outside the Stevenson Ranch Von’s grocery store. But not Jana Baker, she walked casually to her vehicle without any protection from the rain.

“People from Seattle don’t use umbrellas,” said Baker, who moved from Washington state to Stevenson Ranch three years ago. “I love it,” she said. “We need the rain.”

The weather service forecast today’s highs in the upper 40s to mid 50s with possible wind gusts of 60 miles per hour. The snow level is at 5,000 feet but could drop to 4,000 feet on Thursday, Bartling said.