Operation Summer Storm : Weather: Thunder and lightning rock the night sky, cutting off power to thousands, while a downpour makes for the county’s wettest July since 1868.

Thunder and lightning that rocked San Diego County early Wednesday morning resulted in record rainfall, power outages for thousands, flooded buildings and confusion on the highways.

The rare summer storm gave the county its only measureable rain ever on a July 31, with 0.23 of an inch recorded at Lindbergh Field, and made this July the wettest in the county since 1868 and the fourth wettest ever, according to the National Weather Service.

The storm was a continuation of an abnormal weather pattern the area has been experiencing since 1985, such as the current drought and the surge of rain last March, said forecaster Wilbur Shigehara of the National Weather Service.

“We expected the storm to arrive, but not this intense,” he said.

The storm originated in the southern part of Mexico and, instead of dissipating over the Sierra Madre, “this time the storms just hopscotched over the mountains and came here,” Shigehara said.

Rain in July might mean more unusual weather patterns later in the year, he said.

“It’s hard to say what the fall and winter is going to be like, but this says to me that the weather pattern will be more unusual,” Shigehara said.

The following rainfall totals were recorded in San Diego County: Cuyamaca Rancho State Park, 1.71 inches; Escondido, 0.38 of an inch; El Cajon, 0.58; La Mesa, 0.93; Julian, 0.53; Poway, 0.74, and 1.08 inches at the San Diego Wild Animal Park.

Stormy conditions will continue in the East County, mountains and deserts today and Friday, while the beaches, coastal strip and inland valleys will resume being partly cloudy with night and morning low clouds, the weather service said.

Wednesday’s thunderstorms, which began in San Diego about 1:30 a.m., left about 140,000 San Diego Gas & Electric Co. customers in the dark, many of them without electricity for more than 12 hours, SDG&E; spokesman Fred Vaughn said.

Lightning bolts knocked out at least 100 transformers and affected service for customers in the entire southern part of the county, from the beach areas to El Cajon and the backcountry, with outages reported as late as 3:30 p.m., Vaughn said.

Power to all but 8,000 people was restored by 6 p.m., and Vaughn said the utility hoped to have everyone back on line by midnight Wednesday.

At the Rose Canyon Business Park in Clairemont, a power outage was the least of the landlord’s worries.

Management at the 35-acre industrial park had been planning for the past four weeks to replace poorly installed roofs on 11 of the 14 buildings, and work finally began Monday. The day after work on the second roof began Tuesday, the rain started to fall on the building, which was covered only by a thin skin of plywood.

“It was awful,” said Audrey Walker, the on-site manager.

“The reason that this one was even open was that it happened to be a two-story building and the tenants on the top don’t have a means of getting fresh air. We thought that, while it was still cool and overcast, we thought that we could open it up and let some fresh air in and do the tenants a favor.”

Roofers with Commercial & Industrial Roofing Co. jumped the fence at the park at 2:30 a.m. Wednesday to cover the building with plastic tarps and spent the rest of Wednesday nailing down the temporary roofs, Walker said.

In East San Diego, 17 people were evacuated from a two-story apartment house on Ottilie Place when a city storm drain backed up and flooded the ground-floor units, police said.

“It was like a swimming pool,” said Thurno Knuckols, a resident at the apartment.

The American Red Cross is providing accommodations for the families, which include nine children, at a nearby hotel.

Although the California Highway Patrol reported 75 accidents on the county’s highways between 5 a.m. and 2 p.m. Wednesday, there were no fatalities and no major injuries. Parts of Interstate 8 in East County, however, were shut down due to flooding and poor visibility.

Sheriff’s deputies and San Diego police also reported no major incidents related to the weather.