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(CNN) -- After a day of progress against a huge wildfire, crews in Arizona were bracing for Saturday's predicted higher winds and low humidity -- conditions that will make underbrush a tinderbox.
"The weather conditions will be going back to less favorable conditions," said John Helmich, spokesman for the Southwest Interagency Incident Management team.
Wind gusts of up to 30 miles per hour were possible in some areas of the massive fire, forecasters said.
Thousands of firefighters were able to concentrate Friday on "burnout fires," intended to burn ground fuel that feed the large fire, officials said.
Crews were able to keep the fire from crossing into New Mexico.
And, Helmich said, they continued their "absolutely fantastic" effort to build containment lines and save thousands of residences and structures.
The flames have consumed 29 homes, 22 of them in the evacuated city of Greer. More than 5,200 homes are threatened, according to officials.
Jim Whittington, another spokesman, said Saturday will be a challenge.
"High winds, low humidity are all of the conditions necessary for large fire growth," Whittington said. "We know that the winds are going to come up on Saturday, so we have until then to get as much work done and to get to the point where we feel comfortable to where we can sit there and deal with what the winds throw at us."
Only 5% of the wildfire was contained by Friday evening, officials said. The Wallow Fire has scorched more than 408,876 acres, leaving a giant bear-paw-like burn mark on the map of eastern Arizona.
Air and ground crews concentrated on protecting residences and structures in and near the evacuated cities of Springerville and Eagar.
More than 3,000 people are working to douse the fire, from the ground and air. About 221 fire engines and 14 helicopters were in use.
Power companies said Friday that they are still watching the huge fire and its potential impact on crucial transmission lines that supply power to hundreds of thousands.
El Paso Electric said the fire is about 15 miles from lines that serve nearly 400,000 people.
The utility is working with partners and other companies on other sources of power if the lines are closed, company spokeswoman Teresa Souza told CNN. If that occurs, customers in southeastern New Mexico and El Paso, Texas, could see rolling blackouts.
Tucson Electric Power has two lines about 8 miles from the fire. Those lines carry electricity through the region to Tucson.
"We're watching it carefully," spokesman Joe Salkowski said.
If the lines are closed or damaged, the company will be able to prevent outages by using other power sources, Salkowski said.
Tucson Electric Power has a coal-powered plant about 12 miles northeast of Springerville, which is evacuated. Officials are safeguarding the plant, but its distance from the fire and the grassy terrain make it "reasonably protected," the spokesman said.
Meanwhile, authorities were discussing damage caused by the fire with residents in particularly hard-hit communities.
Authorities were notifying residents in the community of Greer, where the wildfire destroyed 22 homes and damaged five others, according to information from the Apache County Sheriff's Office posted on the InciWeb incident information site.
Officials were also notifying residents in Alpine and Nutrioso, where five homes had been destroyed, the site said.
Arizona Gov. Jan Brewer declared a state of emergency earlier in the week to mobilize funds for the wildfires in Apache and Greenlee counties.
The blaze -- about the size of Houston -- has caused authorities to evacuate thousands of people since the wildfire began sweeping through the Apache National Forest on May 29.
Journalist Craig Johnson contributed to this report.