SAN FRANCISCO - Northern California sweltered under record-breaking heat Wednesday that strained electrical grids, intensified wildfire conditions, and buckled the freeway between Sacramento and the Bay Area.
Triple-digit temperatures caused power outages that affected thousands of businesses and stalled subway service across the Bay. Cities issued emergency warnings to keep cool, restrict driving and use less electricity.
Traffic backed up for miles as a high of 109 degrees in Solano County buckled the pavement in three of four lanes of eastbound Interstate 80, the main commuter artery out of the Bay Area.
At the Giants game at San Francisco's Pacific Bell Park, 34 people were treated for heat exhaustion. One person was hospitalized for heat stroke, with a body temperature of 106 degrees.
''Rolling brownouts'' hit the city's South of Market area, where Internet companies are concentrated. Pacific Gas and Electric was forced to shut down power to certain grids for two hours at a time, said Richard Eisner, regional administrator for the state Office of Emergency Services.
The dry conditions and gusty winds prompted a red-flag warning for most of the region, meaning the California Department of Forestry denied fire permits and placed all local fire units on duty.
In Napa, sparks ignited dry grass and 35-mph gusts fanned the blaze, which consumed about 5,700 acres and forced 40 families from their homes. The fire was 35 percent contained by Wednesday evening, and CDF officials expected to have it completely contained by 10 p.m. Thursday.
In Solano County, a cigarette tossed from a car was suspected as the cause of a blaze that burned 1,200 acres and threatened a subdivision and a small herd of cows. It was controlled early Wednesday.
In San Francisco the mercury tied the all-time record of 103 degrees, set in 1988. San Jose and Ukiah hit 104, and Santa Rosa in the northern San Francisco Bay area hit 106. In the Sacramento and Central Valley, temps soared above 106 degrees. Thermal, a small town in Southern California, had a heat index of 123 degrees.
The California Independent System Operator, the agency that monitors the state's electricity flows, forced PG&E to implement the rolling brownouts. About 35,000 businesses and customers, as well as some traffic lights, were affected.
The brownouts started in the early afternoon and were expected to stop at 6 p.m. Customers were also asked to turn off appliances and lights, and ease up on the air conditioning.
Southern California's heat was much less intense, said Jeff Millard, a forecaster with the National Weather Service.
''In L.A. they weren't as bad off today. Most of the heat problems are in the northern part of the state, especially in the Bay area,'' Millard said. ''The high pressure along the coast just won't let the sea breeze in.''
The heat was expected to continue Thursday, with Napa hitting a high of 105 degrees. Winds in Napa were to be light, a possible boon to firefighters. Cooler temperatures were forecast for San Francisco, with a high of 87, and San Jose was to cool off only slightly, to 101 degrees. Sacramento was expected be up near the 106 mark again, and Ukiah was to see another hot day near 104 degrees.
