Rest may be in the forecast for people this weekend, but it looks like air conditioners will be working overtime through Labor Day.

A heat wave that began ramping up Wednesday is expected to continue in Ventura County through the holiday weekend, according to the National Weather Service. Near-record temperatures are predicted.

The mercury is expected to rise as high as 106 in county valleys and into the mid-80s on the coast through Sunday, said Bill Hoffer, a spokesman for the Weather Service's Oxnard office. The heat should decrease by several degrees each day after Sunday, he said.

August is usually a hot month, but temperatures this week are likely to approach some records. The record for Aug. 29 in Santa Paula, for example, is 101 in 1972, Hoffer said.

Extreme heat coupled with crowds of holiday revelers is a recipe for emergencies, and extra firefighters will be standing by to respond, said Capt. Barry Parker, spokesman for the Ventura County Fire Department.

Last Labor Day weekend, the Day fire began and ended up burning 162,000 acres, mostly in Los Padres National Forest. A transient is suspected of starting that fire.

After a year of record-low rainfall, things are even drier this year, Parker said.

"Conditions are much more extreme this year than last year," Parker said. "The potential for a large megafire to occur is there."

Sparks from metal-grinding equipment on private property ignited the Zaca fire north of Santa Barbara on July 4. By Wednesday, it had consumed 240,207 acres of Los Padres wilderness and cost $109 million to fight. The Forest Service on Wednesday announced that some areas within Los Padres that were closed because of the fire will reopen today. The emergency closure area will now involve all forestland between Highway 33 and Highway 166. Pine Mountain Road and Forest Road on the east side of Highway 33 and all recreation areas along the road will remain closed.

To avoid a repeat, Parker said, county residents who plan to work outside with power tools should do so in the morning when it is cool. People should also avoid creating open flames or anything that causes sparks or embers, he said. He also reminded people to stay hydrated to avoid heat-related illnesses.

The heat led state utility officials to issue alerts for Wednesday and today.

With the demand for energy reaching capacity statewide, officials are asking people to switch off unnecessary lights, turn air conditioners up to at least 78 degrees and avoid using major appliances until after 7 p.m.

Edison customers in California used more electricity Tuesday than on any other day so far in 2007, said Rudy Gonzales, a regional manager for the utility. Edison is advising customers to conserve, but the company does not anticipate problems over the holiday weekend, he said.

"Unless anything drastic on the system occurs between now and the weekend, we should be in good shape in terms of meeting customer demand," Gonzales said.