2 Feared Killed in Flash Flood : Weather: A man and his 9-year-old son apparently were swept down a canyon above Sierra Madre. A second day of storms brings lightning and hail to Southland.

A Sierra Madre man and his 9-year-old son were missing and feared dead Monday after a flash flood apparently swept them down Bailey Canyon above their home on Sunday and buried them in the muddy depths of a catch basin.

The search for John Henderson, 34, and his son Matthew continued into the night Monday after more downpours struck Southern California at sunset, pelting Los Angeles with marble-sized hail and snarling homebound commuter traffic.

A lightning strike in South-Central Los Angeles knocked out power to the Metro Blue Line on Monday evening, interrupting rail traffic and temporarily stranding commuters. About 5,000 Los Angeles homes lost electrical service temporarily because of lightning strikes.

Flash flood warnings were issued about 5 p.m. Monday for many of the communities below hillsides stripped of trees, brush and grass during last fall’s devastating brush fires. The only place where damage was reported was the San Bernardino County town of Mentone, where about 50 homes were invaded by water and mud.

Rescuers with search dogs dug through the muck in the Bailey Canyon Wilderness Park catch basin Monday, but they held out little hope of finding the missing father and son alive after digging the boy’s shoe out from under seven feet of mud and water.

Henderson and his son were hiking with several dozen others Sunday afternoon when thunderstorms began raking the fire-scarred highlands above them.

Runoff coursed down the eroding slopes, building swiftly into a torrent that plummeted through the canyon, uprooting trees, unearthing large boulders and smashing a small bridge.

The hikers said they heard a terrible rumbling as the flash flood approached.

“There was no stream at all, maybe a half-inch of water, and then this wall of water came down that you would not believe,” said Neill Southwick, 52, a retired mail carrier. “It was like a dam breaking.”

Southwick said he scrambled up the canyon wall, but others were caught in the rising flood, the water clutching at their drenched clothing and threatening to pull them under. Moments later, the fury of the flood had passed and the torrent slowed, first to a stream and then to a trickle.

Eight of the hikers found themselves stranded on ledges and had to be plucked to safety by helicopter, but most of the others walked out .

It seemed for awhile that everyone had made it to safety. It was not until the rest of the hikers had left that rescuers noticed a lone car sitting empty in a parking lot.

Sierra Madre police traced the plates on the red Honda Civic and discovered it was Henderson’s.

The Sierra Madre Search and Rescue Team, along with canine units from the Los Angeles County Sheriff’s Department and personnel from the Sierra Madre Police Department, searched all night and much of Monday before turning up the boy’s shoe, officials said.

The shoe was found about five feet from the bottom of the catch basin, officials said. The thunderstorms late Monday set off more mudslides that added another seven feet of mud to the catch basin by Monday night, they said.

The search was scaled back at nightfall, but workers from the Los Angeles County Public Works Department brought in backhoes and bulldozers to continue digging through the catch basin after dark.

The thunderstorms Monday evening were largely unexpected. Curtiss Brack, a meteorologist with WeatherData Inc., said a storm system was supposed to tiptoe out of the state during the day without causing much fuss.

“Instead, the storm system just slowed down and decided to sit still for a while,” he said.

Hail was reported throughout Los Angeles, and the Metropolitan Transportation Authority said a lightning strike near the Florence Avenue station knocked out power along a four-mile stretch of the Blue Line. Thirty-six buses ferried passengers around the blacked-out section of the line. Delays of up to 45 minutes were reported. Trains were expected to be back in operation by this morning.

Brack said skies should be mostly clear for the rest of the week, with warmer temperatures. He said rain is not expected again until next Monday, at the earliest.

Times staff writer Nieson Himmel contributed to this story.