Torrential rains that drenched the Bay Area on Sunday, causing flooding and mayhem on the roads and soaking hordes of last-minute shoppers at the malls, should be easing by Christmas Eve, but another storm is expected to follow late Christmas Day.

National Weather Service forecaster Bob Benjamin couldn't say whether Sunday's downpours set any records -- they wouldn't know that until after midnight -- but it sure came down hard. In the 24 hours ending at 4 p.m., San Jose saw 0.97 inches at the airport, and the Santa Cruz Mountains town of Ben Lomond saw 5.39 inches, the region's highest total, he said.

"We've been experiencing just exceedingly heavy rain rates," Benjamin said. "It's just been an extremely intense cold-frontal boundary area. It's brought in a lot of moisture, and once it hit the Bay Area, it started moving through fairly slowly."

The rain was expected to taper off overnight with partly cloudy skies Monday, followed by a moderate storm system arriving Tuesday afternoon that was expected to last into Thursday, Benjamin said. Temperatures were expected to remain in the 40s and 50s through the week.

Sunday's storm led to flash-flood warnings in Santa Cruz and San Mateo counties. Pescadero Creek had reached flood stage. There were no reports of severe weather, but there was some thunder reported midafternoon.

The rain fell so hard and fast that roadways quickly flooded.

At Palo Alto's Page Mill Road and El Camino Real, nearly a half-foot of water covered part of the intersection, where the signal light was flashing red, backing up traffic. On Interstate 280 near Foothill Road, the California Highway Patrol closed two southbound lanes because of flooding. There also was flooding at the Saratoga Avenue offramp. Spinouts and fender-benders lined the sides of the roads and highways.

Power outages

By 9:30 p.m., more than 4,000 customers still were without electricity in the Bay Area and central coast region, including 1,780 in the North Bay, 1,300 on the coast, 380 on the Peninsula, 330 in the East Bay and 275 in the South Bay.

Most of the Peninsula customers without power were in Menlo Park. PG&E crews were on the job, but there was no estimate when power would be restored.

The deluge complicated what already was expected to be a busy day of last-minute shopping.

Debbie and Leon Schmit were taking their granddaughters to see Santa Claus at Westfield Valley Fair mall when the rain started falling so hard they had to stop the car on the Alameda. They ran with the girls into a nearby bookstore to wait out the downpour and got soaked on the way as water bubbled up from the storm sewer and flowed like a river through the parking lot. As granddaughter Liliana Mendoza, 8, ran through the puddle, the water was up to her shins.

"We've lived in San Jose all our lives, and I don't ever remember having to pull over to drive safely," Debbie Schmit, 58, said. "This was an unbelievable storm."

Even so, they continued on to Valley Fair.

"We decided to brave the storm to see Santa," she said.

Kerensa Tryforos of Morgan Hill saw multiple accidents as she and her daughters drove to the mall to make teddy bears for their great-grandparents.

"It's sad to see that around the holidays," Tryforos said. "It's been like monstrous rain all day. I hope Santa doesn't have any problems."

Big-time delays

Commuters also faced multiple delays on the road as accidents quickly piled up Sunday. The CHP responded to multiple vehicle accidents, mainly spinouts, throughout the East Bay as wind and rain held steady. Though the incidents did cause backups, none caused major injury.

Rock slides in Livermore and flooding in Hayward blocked multiple lanes on offramps and on highways.

A high wind advisory was in effect Sunday for three of the four bridges that cross San Francisco Bay. Officials warned people driving campers or hauling trailers to stay off the San Francisco-Oakland Bay Bridge, the San Mateo-Hayward Bridge and the Carquinez Bridge near Vallejo.

Gusty winds were also reported throughout the East Bay on Sunday, hitting as high as 51 mph in Pleasant Hill and 36 mph in Oakland and Berkeley, the National Weather Service reported.

Winds were expected to remain strong throughout the day Sunday before tapering off later in the evening. The next storm system, expected to hit Tuesday afternoon, was not forecast to produce winds gusts as strong as Sunday's.

With the ground already saturated from the previous rain, there could be some flooding of small streams and creeks in Sonoma and Napa counties, though none of the major rivers in the area were expected to top their banks, said National Weather Service forecaster Diana Henderson.

In the Sonoma County city of Petaluma, about 40 miles north of San Francisco, crews were monitoring some areas of the city, but officials were not anticipating major flooding, said Petaluma Fire Department Battalion Chief Jeff Schach.

Whiteout conditions

On Interstate 80 through the Sierra, the main route between Sacramento and Reno, forecasters had issued a winter storm warning, saying that heavy snow and strong winds could create whiteout conditions. For those making the drive, chains were required on tires except for vehicles with snow tires and four-wheel drive. Restrictions were in place from the Placer County community of Gold Run to the Nevada state line.

In Palo Alto, public safety personnel were monitoring San Francisquito Creek levels for hours at the Chaucer Street bridge, where water was below cresting -- but constantly rising. Shortly before 8 p.m., the city warned that, based on current trends, it was likely that there would be overtopping and advised residents to stay in their homes and take precautions to protect their property, including obtaining sand bags at the Palo Alto Airport and Mitchell Park.

For holiday travelers, the storm caused delays at the airports as well as the freeways. With both arrivals and departures running behind schedule and some flights being canceled, people planning to fly out of San Francisco International Airport were being urged by airport officials to check with the airlines on the status of their flights.

Mineta San Jose International Airport spokeswoman Rosemary Barnes said the airport took five flight diversions from San Francisco. San Jose was experiencing half-hour delays throughout the day "due to either weather here or elsewhere."

But only one flight was canceled, and that was due to mechanical issues, not weather, Barnes said. Travelers were advised to check the status of their flights and to arrive early.

"It's a pretty nasty day," Barnes said, "and with the volume of travelers, certainly delays were to be expected."