Firefighters Eye Their Thermometer and Hope

Thursday’s hot weather raised concerns that tinder-dry brush could become fuel for wildfires.

“The winds are our nemesis,” said Chief Scott Brown of the Orange County Fire Authority. “It’s been a quiet season so far, but with temperatures coming up we are monitoring it all. . . . The temperature affects the drying out of the fields. A mere spark created by a shovel on a rock could start a fire.”

Indeed, a wildfire moved rapidly across hillsides south of Corona on Thursday, charring about 250 acres of brush and citrus groves, damaging two houses and prompting the evacuation of more than 200 homes.

The blaze was one of four burning out of control in Southern California and northern Baja California on Thursday night as the area continued to swelter in 100-degree temperatures.

Joan Evans, a spokeswoman for the California Department of Forestry, said the 250 firefighters deployed to battle the blaze in Riverside County were hampered by the gusting winds, high temperatures and low humidity of a Santa Ana weather system that has enveloped Southern California for the last couple of days.

Though much of the summer was unusually mild, the mercury has soared this week. On Wednesday, temperatures were in three digits for Placentia, La Habra, Yorba Linda and Fullerton. On Thursday, temperatures topped out at 101 in Irvine, said meteorologist Scott Breit of WeatherData Inc., which supplies forecasts for The Times. Other local highs were 99 in Lake Forest, 98 in Fullerton and San Juan Capistrano, 97 in Anaheim and Santa Ana, and 84 in Dana Point and Newport Beach.

Today’s forecast calls for highs ranging from 79 in Newport Beach to 94 in Fullerton and Irvine.

Brown of the fire authority said, “These are the critical months. The change we’re seeing now is sustained warmer temperatures. In the back country, it’s extremely hazardous.”

Six years ago this month, brush fires destroyed more than 300 homes in Laguna Beach.