Fire managers northwest of Helena say the Horsefly Fire grew to 1,294 acres overnight.
Firefighters focused on protecting homes and structures in the Flesher Acres and Flesher Pass area Tuesday night.
As of Wednesday morning, no structures have been reported as lost or destroyed.
According to the fire information site Inciweb, the fire grew to the east-southeast. It continues to burn through beetle-killed timber.
Fire managers say if behavior becomes extreme over the next 24 hours, there is the potential for the fire to cross Highway 279. However, if cloud cover and higher humidity continue, fire spread should be limited.
Firefighters are watching for the potential for thunderstorms on Wednesday and Thursday and say that could drive the fire or create new fire starts.
Highway 279 is closed to bicyclists and previous evacuation orders remain in place. People traveling in the area need to be alert for firefighters and firefighting equipment.
The Horsefly Fire started on Monday, August 5 northwest of the Black Diamond Fire and consumed that fire. The cause of the fire has not been determined.
The public can call 406-458-4992 for information about the fire.