We drove through Montana on 8/25/17 to get from Buffalo, WY to Kalispell, MT. We did the drive in 3 days making two stops.
There are several fires burning in Montana; we passed several small burned areas near the freeway and could see a lot of smoke in the air near Butte MT. While spending one night near Butte I didn’t go outside as the smoke was so thick.
Here’s a picture of how smoky the air was around Butte: