Firefighters are taking advantage of better weather to set backfires and shore up the fire lines on the eastern flank of the giant wildfire burning in Southern California.

After more than two days of delays, weather conditions improved Wednesday night, allowing crews to begin burnout operations to destroy fuels that would help spread the 15-day-old blaze in the Angeles National Forest.

Fire officials are racing to clear the brush ahead of a high-pressure system that is expected to build across Northern California on Thursday and Friday, bringing warmer and drier conditions across Southern California.

The arson-caused fire has burned across 160,357 acres, or 250 square miles, of the San Gabriel Mountains north and east of Los Angeles since it was set along a forest road Aug. 26.

With 19 miles of fireline left to cut in steep and forbidding wilderness, hot and dry conditions on Wednesday pushed plans to set backfires into the night as crews waited for the weather to cooperate.

Containment notched upward to 62 percent and there was no increase in size, said Darryl Jacobs, a spokesman at the fire command post.

PHOTOS: California Wildfires Rage Near Los Angeles

At least two dozen helicopters and airplanes were attacking the blaze, along with 3,647 firefighters, as more crews were released back to their home stations.

But since Monday, unpredictable winds have foiled firefighters' plans to use backfires to contain the eastern flank in the San Gabriel Wilderness, an incredibly rugged preserve in the forest where elevations range from 1,600 feet to 8,200 feet and growth ranges from chaparral to pine and fir.

After days of delays due to low humidity, fire officials finally began burn out operations on Wednesday evening, Jacobs said.

Temperatures in the Los Angeles region have been more moderate this week than in the first week of the fire, when high heat and little air movement clamped a smoky lid on the metropolitan area. Breezes from the ocean have since cleared the air and a deep marine layer has moved well ashore during overnight hours.

Morning moisture and dew might also allow helicopters with torches burn through the steep canyons around Mount Wilson and build a substantial buffer around its historic observatory and television, radio and cell phone transmission towers, Jacobs said.

Crews hope to clear brush before warmer and drier conditions return to Southern California on Thursday and Friday, as a high-pressure system builds across Northern California.

The fire command post was moved eastward this week from Los Angeles to Irwindale, a small industrial city closer to the active east end of the blaze.

Residents of the suburbs below the southern face of the San Gabriels were getting updates on the fire's status online.

Two firefighters were killed Aug. 30 when their truck plunged off a mountain road, which has made the arson probe a homicide investigation.

The fire has destroyed 78 residences, two commercial properties and 87 outbuildings. It has damaged 13 residences, two communications sites, one commercial property and 30 outbuildings.

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