By Keith Coffman

(Reuters) – A lightning-sparked wildfire burning for more than a month in western Montana has flared anew, prompting the evacuation of nearly 750 homes on Thursday as firefighters braced for more hot and windy weather forecast for the weekend, authorities said.

The so-called Lolo Peak fire, burning about 12 miles south of Missoula, has scorched more than 15,000 acres of timber since it erupted in mid-July, as tinder-dry conditions challenged efforts to contain the blaze.

“When the winds kicked up last Sunday, it made a run of one and a half miles in an hour and has been growing since,” U.S. Forest Service spokesman James Stone said.

Erratic winds pushed flames close to housing subdivisions in two counties on Thursday, prompting mandatory evacuations of residents from 743 homes, said Jordan Koppen, a spokesman for the fire management command.

Fire retardant drops from helicopters and fixed-wing aircraft have been deployed to douse the flames in an effort to assist some 500 firefighters on the scene.

No property losses have been reported, but a 29-year-old member of an elite “hotshots” firefighting crew from California was killed this month when a falling tree struck him.

Koppen said weather forecasters have issued red-flag warnings for the area on Friday, and he expects the burned acreage to increase when the fire is mapped again Thursday night.

The northern Rocky Mountain region has been in the grips of a prolonged drought, and this year wildfires have blackened 393,000 acres in Montana and parts of neighboring Idaho, Stone said.

In Oregon on Thursday, Governor Kate Brown authorized the state’s fire marshal to mobilize additional resources to aid local firefighting efforts near the Cascade town of Sisters, where a wildfire threatened more than 400 structures. An estimated 1,200 residents of the area were advised to stand by for possible evacuation notices.

(Reporting by Keith Coffman in Denver; Editing by Steve Gorman and Leslie Adler)