Record-breaking heat hammered the northern Rockies on Tuesday and smoke from dozens of large wildfires drove pollution to unhealthy levels — a grim but increasingly familiar situation for a region racked by drought.

Unhealthy air was recorded around most of Montana’s larger cities — Billings, Butte, Bozeman and Missoula — and in portions of northern Wyoming and eastern Idaho, according data from U.S. government air monitoring stations.

More than 40 large fires were burning in the three states, and smoke was also pouring in from blazes on the West Coast.

Meanwhile, dangerously hot conditions baked communities across eastern Montana and northern Wyoming.

Billings reached 106 degrees Fahrenheit (41 degrees Celsius), topping the previous record for the day set in 1947. It was the fourth record daily high tallied in Montana’s largest city so far this month. Miles City and Sheridan, Wyoming also set records.

Even before Tuesday it ranked as one of the hottest Julys on record, National Weather Service forecaster John Wetenkamp said.

“Without the smoky skies we probably would have been a few degrees higher,” he said.

Across the U.S. West, firefighters have confronted an unusually large number of early season wildfires this summer as drought grips a region that’s also warming due to climate change. That’s making it harder to control and put out fires that have been blanketing much of the nation with smoke in recent days.

Residents of the Rocky Mountains are accustomed to some smoke during the summer. But air quality this year has worsened earlier than usual — and persisted.

A June heat wave that coincided with several major fires dried out the vegetation in forests and set up the landscape for more fires as the summer has advanced, said air quality specialist Benjamin Schmidt with the Missoula City-County Health Department.

Large fires sometimes burn into October. If that happens this year, Schmidt said, the Missoula area could experience its longest smoke season recorded to date, exacerbating public health impacts.

“If you have medium levels of smoke for two days, that’s totally different from two months of smoke,” he said. “Now you’re starting to get headachy more easily and for people who have inflammation-type diseases, it affects the heart, respiratory system, everything.”

The smoke can take a little edge off the heat if it gets thick enough to block out sufficient sunlight to keep temperatures down, Schmidt said. But that also can create conditions that prevent mixing between different layers of the atmosphere, allowing the smoke to linger.

The hot and dry conditions contributed to a fire southeast of Cascade in central Montana doubling in size overnight. The blaze in the Harris Mountain area has burned nearly 30 square miles (77 square kilometers), prompting an evacuation order for 60 homes.

Crews successfully defended the homes from encroaching flames Monday night and were expected to do so again Tuesday, fire operations spokesperson Sara Rouse said.

“Point protection around and near structures has been occurring and will be ongoing,” she said.

More than 200 firefighters have responded to the lightning-ignited fire Friday. They were among about 5,000 firefighters deployed across the Northern Rockies as of Tuesday.

Cooler temperatures were forecast for later in the week. But potential thunderstorms could bring winds, stirring up blazes, and lightning to start new ones.

Pollution levels were high enough over a 24-hour period that Montana officials issued an air quality alert and recommended people limit prolonged activity in Bozeman, Broadus and Hamilton. Children, the elderly and people with heart disease or respiratory ailments are most at risk, state officials said.

An air quality alert also was issued for Lemhi County, Idaho.

Growing scientific research points to potential long-term health damage from breathing in microscopic particles of smoke.

N95 masks can protect against wildfire smoke but need to fit properly to be effective. When the smoke gets bad, health officials recommend keeping doors and windows closed, and running an air filter to clean inside air.

The number of unhealthy air quality days recorded in 2021 by pollution monitors nationwide is more than double the number to date in each of the last two years, according to Environmental Protection Agency data. Wildfires likely are driving much of the increase, officials said recently.

(AP)