(CNN) -- Firefighters fared better than they expected battling the raging blaze in Arizona on Friday due to high humidity, cloud coverage and lower winds than expected, a fire department spokeswoman told CNN.
Light showers on the southwest flank of the fire also aided the firefighters, said Barbara Bassler, the public information officer for the fire department. The department estimates that the fire will be fully contained on July 2, she said.
Forecasters predicted that winds could fan a raging blaze that has torched more than 15,000 acres in northern Arizona, but U.S. Forest Service spokesman Willie Begay said earlier Friday that firefighters were "confident they can hold the lines today."
Crews had gained traction against the Schultz Fire in rugged, mountainous terrain near Flagstaff on Thursday, raising the containment level to 50 percent, mostly on the northeast, east and southeast flanks of the blaze. The gains included conquering two spot fires outside the perimeter and a successful overnight controlled burn to eliminate potential fuel on the fire's southwest side, fire spokesman Eric Neitzel said Friday.
Begay said the area was covered by clouds most of Friday morning, and then the sun started to break through. He said the winds had been steady in speed but erratic in direction. Firefighters were hoping the wind wouldn't shift and blow the blaze toward the vulnerable western flank.
Weather forecasters had predicted winds from the southwest winds with a slight chance of isolated afternoon storms. CNN meteorologist Sean Morris warned there may be gusty winds up to 30 mph overnight into Saturday.
Fire crews were working Friday to construct, improve and burn out fire lines on the southwest and northwest sides of the fire, while patrolling and mopping up the contained areas, Neitzel said. On the west side, where flames were licking at wilderness areas, Neitzel said firefighters would be using "minimum impact suppression tactics" to lessen impact on the land.
"No bulldozers. No machines," he said. "Trying our best not to disturb [the wilderness] but take care of the fire."
More than 900 firefighters from several Western states have been working on slopes up to 10,000 feet high since Sunday. Those slopes can funnel winds and worsen fire conditions.
The fire started Sunday from an abandoned campfire and the Forest Service is offering a $2,500 reward for information about who may be responsible. As of Friday morning, it had cost more than $5 million to combat the blaze, according to the Incident Information website.
The flames have threatened homes, critical watersheds and wilderness administered by the Coconino National Forest. Hundreds of people were evacuated from the fire's east flank after the blaze started, but many were allowed to return Wednesday.
CNN's Mark Morgenstein contributed to this report