SANTA ROSA, Calif. — Crews on Wednesday continued to increase containment of a cluster of deadly wildfires that have ravaged Northern California, while authorities announced the discovery of another fire victim — a development that brought the fatality count to 42.

After more than a week of warm days and extremely dry air that helped keep the fires raging, a cooler weather pattern began to settle in.

The combination of light winds, increased moisture and lower temperatures has aided firefighting efforts across the region, Cal Fire spokesman Daniel Berlant said.

Firefighters took advantage of the favorable conditions to conduct firing operations Tuesday night.

A back-burning operation on the north end of the Pocket fire, the smallest but least contained of the fires in northern Sonoma County, stymied the blaze’s potential to race out of control, officials said.

Cal Fire operations Chief Steve Crawford told crews that Wednesday was the day to push the fire’s containment deeper into itself until it burns itself out. The Pocket fire had burned 12,430 acres and was 63 percent contained.

Fire crews also burned vegetation in the path of the 54,423-acre Nuns fire, Berlant said, burning in the hills connecting Sonoma and Napa counties.

The Oakmont fire, an offshoot of the Nuns fire that ignited Saturday, had connected with the rest of the blaze on the northwest flank. Crawford told crews to patrol the area for any new flames.

Firefighters took a direct approach with the Tubbs fire to the south, Crawford said. Crews on foot and by air directly attacked flames creeping downhill toward Napa Valley.

The deadliest of the blazes, the Tubbs fire, was mostly under control by Wednesday. After scorching 36,432 acres and leveling much of the city of Santa Rosa, it was 91 percent contained.

Firefighters were essentially in a mop-up phase for much of the area, where crews are patrolling for hot spots that could rekindle and chew through unburned vegetation, Crawford said.

“There’s a lot of cautious optimism in terms of final containment, but we’re still not there,” Sonoma County spokesman Barry Dugan said. “We also understand that these fires can be volatile and weather can change.”

Most Sonoma County evacuation orders have been lifted for areas that weren’t burned, but residents in burn areas are still barred from returning home, as are evacuees from Geyserville and parts of the Sonoma Valley, Dugan said.

In Napa County, firefighters continued to uncover more damage from the deadly Atlas fire that raced west down Atlas Peak on Oct. 8, killing six people. The 51,064-acre fire was 83 percent contained Wednesday.

The total number of buildings destroyed by the blaze Wednesday stood at 421, with another 66 damaged.

All mandatory evacuation orders have been lifted in Napa County, though some roads are still closed, Napa County officials said Wednesday morning.

“As some residents are allowed to return to their homes, please drive carefully as emergency personnel are still working throughout the fire area,” authorities warned in a Cal Fire incident report.

In Mendocino County, the Redwood fire had burned 35,800 acres and was 70 percent contained as of Tuesday night. Residents were returning to their homes there as well, after the Redwood and Sulphur fires combined to destroy 680 structures.

“The Redwood Fire efforts are progressing toward full containment,” according to a Cal Fire incident report Tuesday. “Firefighters will extinguish hot spots around structures and actively mop up as residents repopulate the effected fire areas.”

joseph.serna@latimes.com