Thick smoke in Northwest Montana helped dampen fire growth on what had been predicted as a critical fire day.

But it was a double-edged sword, with fire officials noting that the dense smoke precluded helicopters from flying safely.

No helicopters have been able to fly since Sunday over the large Bear Creek and Trail fires burning on the Spotted Bear Ranger District of Flathead National Forest.

“We haven’t been able to get aircraft up in the air, and even when we did, like yesterday, the smoke was still hanging pretty good in the valleys and we couldn’t see it very well,” information officer Al Koss said on Monday.

“Over the last couple days we’ve been having this inversion of smoke that hasn’t been breaking until two or three in the afternoon. ... We’ve been having moderate fire behavior even through it’s been warmer and the relative humidities have been lower.”

Typically, humidities below 20 percent are seen as a risk for active fire weather, but Koss said even humidities as low as 10 percent haven’t caused significant fire growth since the heavy smoke rolled in.

At the Thompson-Divide Complex at the southern edge of Glacier National Park, the Sheep Fire had little growth by Monday afternoon. It is still estimated at about one mile south of Essex and a half-mile from U.S. 2.

Winds in the area stayed relatively calm despite the forecast, and Sonja Hartmann, a spokeswoman for the team fighting the fires in that complex, added that an inversion helped keep a lid on the fire through most of the day.

However, it complicated efforts to fly crews in to continue mop-up operations at the Thompson Fire in Glacier National Park.

“They had plans to put crews back in there, but they couldn’t do it safely with the smoke,” Hartmann said. “It’s really been with us all day. We expected the winds to come in and clear this out, but it never came — which is a good thing.”

She added that hand crews were able to work around that problem on the Sheep Fire by entering the area by train, then building fuel breaks throughout the day.

Reporter Samuel Wilson may be reached at 758-4407 or by email at swilson@dailyinterlake.com.