Nearly four months before the heart of wildfire season, thousands of Bend residents woke up Monday morning to a layer of smoke over parts of the city.

The smoke was the result of a 324-acre controlled burn near Bend’s western edge Sunday, combined with a weather pattern that caused it to linger over the city. While the smoke disappeared as quickly as it arrived Monday morning, it left Bend with several hours of air-quality numbers reminiscent of last year’s wildfire season.

At its peak Monday morning, the level of particle pollution in the air was comparable to what Bend saw in September, when the Milli Fire burned 24,000 acres outside Sisters.

“Those are the values we see during a severe wildfire,” said Greg Svelund, spokesman for the Oregon Department of Environmental Quality’s eastern region, which includes Deschutes County.

Going into the weekend, fire specialists from the Deschutes National Forest intended to ignite only about 150 acres of forest near the Rimrock trailhead, a mile southwest of Bend’s urban growth boundary off Cascade Lakes Highway. Because of favorable weather, the Forest Service got permission to burn the entire parcel.

The prescribed burn was part of the Forest Service’s effort to reduce fuel for wildfires later this summer. Alex Enna, prescribed fire manager for the Deschutes National Forest, said the burn was particularly vital, given the parcel’s proximity to Bend and the amount of fuel that had built up in the area.

“Those areas are the most important for us, but they’re some of the most difficult,” he said.

The Forest Service had planned another controlled burn Monday, on a 77-acre parcel on the north side of Skyliners Road, but Tom Jenkins, a meteorologist with the Oregon Department of Forestry, said the agency didn’t authorize another burn with smoke still in the air.

Enna said the Forest Service was still planning to burn about 109 acres on Tuesday, across the road from the Rimrock burn, if weather conditions hold. While the burn would not be as ambitious as Sunday’s, he said, it could still impact Bend residents.

“There’s still going to be some amount of smoke,” Enna said.

The forecast Sunday included clear skies with winds out of the northeast, which would push smoke away from Bend. In other words, it was a great day for prescribed burns.

“The weather pattern that we had … was about as favorable as the weather gets in spring,” Jenkins said.

Because of that, Jenkins said the state forestry agency gave the Forest Service permission to ignite the full 324-acre parcel. Enna added that completing the entire project in a single day prevents the Forest Service from closing the trail twice and saves the agency time and money.

The result was a robust column of smoke that was visible from a lot of Bend on an otherwise clear Sunday afternoon. For much of the afternoon and evening, the air quality in Bend remained relatively normal as prevailing winds carried the smoke away from the city.

However, an inversion — a weather pattern that occurs when temperatures near the ground are cooler than temperatures higher in the air — settled over Central Oregon that night. Jenkins said inversions aren’t uncommon in the region during spring, and they tend to push smoke toward low-elevation parts of the city, including the Deschutes River corridor.

Svelund said the smoke accumulations peaked around 9 a.m. Monday, with levels that have not been seen in Bend since summer, when smoke from the Milli Fire forced organizers to cancel events and left much of Central Oregon with unhealthy air for parts of August and September.

While the smoke impact Monday was minimal by comparison, Svelund emphasized that breathing unhealthy air even for 90 minutes can cause dry eyes, coughing and shortness of breath. People with asthma and related conditions can expect to see those conditions worsen.

After the sun rose and the air began to warm, the smoke in Bend dissipated fairly quickly. By noon Monday, the air quality was back within the normal range, Svelund said.

— Reporter: 541-617-7818, shamway@bendbulletin.com