TUCSON, Ariz. (AP) — Hundreds of people were under an evacuation order and 1,200 more were to prepare to go Friday as firefighters worked to keep a wildfire from moving downhill from canyons and ridges in mountains in a national forest on the outskirts of Tucson, Arizona.

Most of the western United States is experiencing extreme dryness or drought, creating challenging conditions for wildfire season, Bryan Henry, meteorologist with the National Interagency Fire Center, said in a recent fire season outlook.

Authorities have said southern Arizona's dry, hot weather and the steep, rocky topography have been the main challenges in fighting the fire. Friday was the hottest day yet for crews battling the blaze, with temperatures forecast to reach 107 (41.6 Celsius) in the afternoon.

National Weather Service forecasters said temperatures were projected to remain in the triple digits through the weekend with a 10% chance of dry thunderstorms or potentially dangerous downbursts that bring only a trace of moisture but can kick up gusts of wind that feed flames.

“We do have some weather concerns," said incident meteorologist Gary Zell, who was stationed Friday at now-closed Catalina State Park.

“These guys are heroes, working all day in up to 107 degrees (41.6 Celsius)," said Zell, who has worked wildfires around the West for two decades. “This is the first time I've worked a fire in my hometown so I'm pretty vested in making sure everything goes well.”

Authorities said the fire’s growth slowed overnight Thursday but that it remained a threat. Flames have been visible from Tucson at night, and smoke from the fire plumed over a suburb Friday morning.

The firefighting effort will get help from Federal Emergency Management Agency, which officials say has granted Arizona’s request for federal funds.

The fire, sparked June 5 by lightning, was only 10% contained as of Friday morning. The National Wildfire Coordinating Group said in its daily operation plan that containment may not be achieved for weeks.

Pima County officials on Thursday issued an evacuation notice for approximately 300 homes in a area south of the Coronado National Forest. Residents of some 1,200 other homes were told to prepare to evacuate as well, said Deputy James Allerton, a sheriff's department spokesman.

As of Friday, the fire had burned 11 square miles (29 square kilometers) of mostly brush and tall grass. Specialized crews were assessing potential threats to homes and other structures to identify access routes and develop contingency plans in case the fire spreads into residential areas.

In the neighborhoods closest to the fire, sheriff's deputies checked IDs to confirm that people trying to enter were residents, as helicopters dropped water on hot spots.

Sheriff's officials went door to door in neighborhoods on Thursday to notify residents of the evacuation notice, which a sheriff's spokesman said Friday wasn't mandatory.

“People are not required to leave, however we are telling people we may not be able to come back and assist if things start to burn," said Deputy James Allerton.

No injuries or structural damage was reported, Allerton said.

Travis Mayberry, an operations section chief for the fire management team, said Friday much of the fire was burning in terrain too rugged for grounds crews to work safely, particularly if they needed to escape quickly.

”Ït's not a great place for us to put people in to safely work," he said. “Ït's just too steep.""

In Oro Valley, on another side of the Santa Catalina mountains, dozens of people parked their vehicles Friday afternoon alongside State Route 77 to watch three helicopters battling flames descending the slopes as smoke poured into the sky.

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Anita Snow reported from Phoenix. Paul Davenport in Phoenix also contributed.