The high-pressure system of warm, dry air that pushed temperatures into the triple digits in Southern California will begin to drift away beginning Monday, bringing a dip in heat to the area.
The Los Angeles area will see temperatures in the high 70s, and desert temperatures will fall into the 90s by midweek, said weather specialist Stuart Seto.
The cooler temperatures should help the nearly 2,000 firefighters battling the Lake fire in the San Bernardino Mountains south of Big Bear Lake.
The blaze, which began Wednesday, has scorched more than 17,050 acres. Several hundred people evacuated campsites and vacation homes.
The fire tore through dry, rugged terrain that has not seen a fire this large in more than a century, officials said. The forest is particularly vulnerable to fire because of a bark beetle infestation that has killed many trees.
"It's steep and there's a lot of dead trees that are down," fire spokeswoman Shawna Hartman said. "The logs will burn, roll down the hill, then catch something at the bottom of the hill, sending the fire back up."
The fire, which was pushing in a southeasterly direction toward the Morongo Valley, was 19% contained Sunday, according to the U.S. Forest Service.
About 500 homes and other structures were threatened by the blaze, but no structural damage has been reported, Hartman said. A plume of smoke extended hundreds of miles east over the Mojave Desert. Air quality warnings have been issued in the area.