Step by step, with a little help from the weather, firefighters in Southern California are regaining control of three wildfires that have destroyed dozens of buildings, burned more than 100,000 acres and left countless residents homeless for days.

Cooler temperatures have helped firefighters on the ground slow the rapid pace of extinguishing the fires and significantly increase their effectiveness, but crews are not letting their guard down.

“We’re not letting the weather fool us,” said Kenichi Haskett, public information officer for the Los Angeles County Fire Department, regarding the bridge fire. “I know the weather is cooperating, but we’re still dealing with challenging conditions.”

Containment on the 52,487-acre Bridge Fire rose to 3% Friday after days of flames moving north over the Angeles and San Bernardino national forests, with crews unable to contain any of the fire’s perimeters. More than 5,000 structures remain threatened by the flames, and dozens of structures have been destroyed. At least 13 homes in Wrightwood and nearby cabins have burned.

Firefighters there — and those to the east battling the Line fire and to the south battling the Airport fire in Orange and Riverside counties — were hoping for a break from several days of extreme heat and low humidity that would give them a chance to begin extinguishing the out-of-control blazes.

Firefighters battling the bridge fire Friday were focusing their attention on its north slope, protecting the communities of Piñon Hills, Wrightwood and Mount Baldy Village, Haskett said.

Authorities also began lifting evacuation warnings in San Bernardino County on Friday afternoon as the fire threat in some locations began to ease.

Haskett said that while conditions have improved, firefighters are still having to contend with difficult, uneven terrain, making it difficult to access certain areas and build containment lines.

Dry brush and vegetation also contribute to the irregular spread of the fire. The flames spread quickly and sometimes change direction.

Light rain is possible on Sunday evening and Monday morning.

“That will help bring the temperature down a bit and increase the humidity, but it doesn’t mean the fire is out,” Haskett said. “They still have to go through log by log and rock by rock.”

The Line Fire in San Bernardino County has increased to 21% containment from Wednesday to Thursday. The blaze expanded by less than 400 acres overnight Friday to 37,963 acres, according to the California Department of Forestry and Fire Protection website.

This week, a 34-year-old Norco man was arrested on suspicion of starting the Line fire and charged with multiple counts of arson. Prosecutors say Justin Wayne Halstenberg tried to start the blaze several times before it finally caught fire.

His mother, Connie Halstenberg, told The Times that her son is innocent.

“He did not light that fire, I repeat, he did not light that fire,” she said.

Firefighters say the weather, especially higher humidity levels, helped crews build lines as the fire began to burn itself out.

Firefighters hope that these favorable weather conditions will continue over the weekend.

Temperatures in fire-affected areas will continue to drop throughout the weekend and into the rest of next week, said Sam Zuber, a meteorologist with the National Weather Service in San Diego.

“We were very fortunate to get into this extended colder period and everyone is grateful that they were able to get the fire under control,” Zuber said.

High temperatures next week are expected to be in the upper 70s or lower 80s, about 10 degrees below normal for this time of year, she said. In the high peaks of the San Bernardino Mountains, temperatures could peak in the 40s by Monday.

There could even be a chance of rain near the bridge fire on Monday, Zuber said, with about a tenth of an inch of rain possible that day. The amount of rain shouldn’t pose a risk of mudslides in the fire areas.

Relative humidity is also expected to increase to as high as 60% by Monday, which could further complicate fire development.

“In such high humidity, the fire will have difficulty spreading,” she said.

Zuber said the only reason for concern is that cooler temperatures could bring stronger winds, with gusts of around 20 to 25 miles per hour starting Sunday.

And the fire remains a threat. Officials said patches continue to smolder, with flames sporadically spreading up slopes and drainages, using dry vegetation as fuel.

Authorities said more than 65,000 buildings were still at risk of fire.

“Our goal is to build direct and indirect fire lines,” said Fabian Herrera, spokesman for the Line Fire Unified Command, which includes Cal Fire and the San Bernardino National Forest.

Herrera said the priority is to stop the fire from spreading to the north and keep it at a safe distance from communities.

“The weather forecast for the weekend and early next week seems very positive, but everything could change if the weather changes or the wind increases,” he said.

He added that crews battling the line, bridge and airport fires are currently sharing air resources, dropping water and fire retardant on three large wildfires.

He added that damage inspection teams had already started visiting communities to assess the impact of the fires, but the total cost of the firefighting operation had not been estimated.

So far, three structures have been damaged by the Line fire, and one has been destroyed. In the airport fire, 22 structures have been destroyed, and another three have been damaged.

Robert Rice of the California Department of Forestry and Fire Protection looks closely at the remains of the bridge fire in Mount Baldy Village on Thursday.

(Genaro Molina / Los Angeles Times)

Containment on the airport fire also increased Friday morning, rising to 8% from 5% the day before. The blaze was listed at 23,494 acres. Crews there are assessing how many homes were destroyed in El Cariso Village, tucked away in the Santa Ana Mountains, after the fire jumped Ortega Highway earlier this week and ran through the small community.

Officials began scaling back evacuations Thursday due to the favorable weather, including some residents of Lakeland Village near Lake Elsinore and Rancho Carrillo in Riverside County.

In Orange County, residents along Ortega Highway up to the Nichols Institute were allowed to return as a mandatory evacuation order was downgraded to a warning.