SAN DIMAS, Calif. (KABC) -- The city of Glendora raised its storm alert level to red on Thursday night, meaning residents will be urged to evacuate on a mandatory basis from homes near the Colby Fire burn area. The alert was raised at 10 p.m.
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An evacuation center has been established at the Teen Center, 241 W. Dawson Ave.
Goddard Middle School at 859 East Sierra Madre Avenue will be closed Friday. Glendora Mountain Road and Big Dalton Canyon Road were also closed until further notice.
The increased alert level comes ahead of a powerful storm that's expected to douse Southern California.
The heavy rain is set to hit overnight, starting with Ventura County and pushing into Los Angeles County by early Friday morning.
Hunkering down in the danger zone, residents took extra measures after watching the storm pound Northern California Thursday.
Glendora residents Howard Romero and his wife hammered in wood barriers across their driveways Thursday morning. It's the second week in a row they're preparing for potential mudflows from the hillsides, charred by the Colby Fire. The blaze burned nearly 2,000 acres in January.
City and county officials are concerned a heavy amount of rain could cause the hillsides to break loose.
"We're going to strongly advise that for their safety they should leave their residence," said Glendora police Chief Tim Staab. "There's nothing they can do once the rains come and the mud starts to flow."
Glendora resident Richard Pope already had sandbags around his property, but he said he saw the forecast and stopped by the city yard to pick up more.
"Doesn't look too promising. We need the rain but not all at once," Pope said.
Hillsides are dissolving where Colby Fire strafed the ground cover. The greatest risk is at Ed Heinlein's Azusa home, in a vortex of the mudflow.
"It will crush the house, the house will go off the foundation and be out in the street."
The slope behind Heinlein's home is bigger, steeper, and the catch basin is his backyard.
"Sooner or later, this stuff is coming down," Heinlein said.
He shared lessons learned after so many inundations. First, write down your action plan "because when the rain starts and the problems come that you don't expect, you don't think," Heinlein said. Next, prepare for that insurance claim.
"You need to video today everything in your home and around your property," he said.
Heinlein has spent $40,000 on fencing, plywood, plastic.
The combination of strong winds and rain also causes a real concern for power outages. Southern California Edison crews said they'll be mobilized and ready for repairs. They are staging for downed trees, outages, whatever could come.
"A lot of very, very mature trees can't handle any more water in the ground and so they uproot trees, they go through overhead facilities and those cause power outages," said Steve Conroy with SCE.