It rolled in heavy and smelly, but the smoke that suddenly blanketed the Missoula and Frenchtown valleys Friday evening didn't come from Montana.
Two prescribed burns on the Nez Perce-Clearwater National Forest, on the Idaho side of the Bitterroot Mountains, are to blame.
“You can certainly see on satellite two separate burns coming over the top right into us,” said meteorologist Travis Booth of the National Weather Service station in Missoula.
The Lolo National Forest said on Facebook and Twitter that a prescribed burn Friday on the Ninemile Ranger District was cancelled. The fire crew spent the day monitoring and securing the edge of Thursday’s burn.
“The smoke settling in the Frenchtown Valley is coming from out of area,” the Lolo forest's message said.
Air quality at Frenchtown jumped two levels between 4 p.m. and 6 p.m., from Moderate to Unhealthy. The air monitor in Missoula spiked from Good to Unhealthy for Sensitive Groups between 6 p.m. and 7 p.m.
The Nez Perce-Clearwater gave notice of the burns and said residents of Missoula and the Bitterroot Valley “are likely to see smoke from the prescribed fire on the North Fork and Lochsa Ranger Districts.”
“Prescribed fire produces smoke, but the smoke is typically visible for a short duration, 3-4 days, and managed to minimize impacts to communities,” the message said. “Prescribed fire and other fuels treatments help to reduce the severity of wildfires and minimize long-term adverse smoke impacts on public health and safety.”
Booth said most of the smoke was likely to drift southward Friday night into the Bitterroot Valley so there was likely to be some improvement in Missoula.
“I would imagine we’ll still have haze or patchy smoke tomorrow,” he said.
How long it’ll last “probably depends on prescribed burning,” Booth added. “We do have a cold front coming in, but overall we’re still going to have westerly wind flow.”