Ash rain reported in Treasure Valley due to smoke from wildfires

If you thought Boise’s air quality couldn’t get much worse, think again.

The National Weather Service in Boise received reports of ash falling from the air Tuesday morning in the western Treasure Valley, including in Weiser, Nampa and the west side of Boise Bench.

The Treasure Valley has spent most of July under a blanket of smoke, while the Cow Valley and Durkee Fires continue to rage in eastern Oregon. The Cow Valley Fire is 78% contained, but the Durkee Fire continues to grow just west of Interstate 84 and has been responsible for sending heavy smoke across the Gem State over the past week.

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The rapidly growing Durkee fire and associated smoke have been exacerbated in recent days by strong east winds blowing thick plumes of smoke toward Boise.

The Idaho Department of Environmental Quality on Tuesday issued its first red air quality advisory of the year. The advisory, labeled “unhealthy” and the fourth-highest advisory level of the six, warns that children, the elderly and people with heart or lung conditions should avoid prolonged or strenuous exercise.

But how did it get so bad that ash was falling from the Treasure Valley sky?

Ash rain from above in Idaho

It is very unusual for ash to fall from the sky when there is no active forest fire or, in most cases, fallout from a volcanic eruption.

However, there were multiple conditions Monday and Tuesday that allowed the Durkee fire to produce “pyrocumulus clouds,” National Weather Service meteorologist Stephen Parker told the Idaho Statesman on Tuesday.

“It was what we call extreme fire behavior yesterday,” Parker said. “That’s when the fire becomes plume-dominated, and we were so unstable (in the atmosphere) that the fire was able to essentially create its own thunderstorm overhead and create pyrocumulus clouds.”

The searing temperatures inside the fire can carry the ash high into the atmosphere, Parker said. From there, the hot air condenses and forms clouds, but the ash is still trapped at a much higher altitude than normal.

Normally, ash would fall near the fire. However, pyrocumulus clouds cause the ash to drift far from the source of the fire before eventually falling on unexpected people below.

How long will the air quality in Boise remain bad?

If you’re someone who struggles with poor air quality… bad news.

Parker expects the smoking situation to get worse before it improves.

“The latest information is that we’re going to stay like this for most of (Tuesday), but tonight (Wednesday) it should get worse,” Parker said. “Thursday should at least be a little bit better, but these forecasts are only for 48 hours because it’s very hard to predict.”

Weather Service meteorologist Josh Smith said the best chance for thunderstorms this week is Wednesday night, which would help push smoke out of the Treasure Valley. There is only a 20 percent chance of storms for Boise, but rain from 70 mph could bring brief heavy downpours and small hail.

On Wednesday, the air quality in the Treasure Valley could at times fall into the purple “very unhealthy” category. The “very unhealthy” category warns that children, the elderly and people with heart or lung conditions should avoid all outdoor activities, while everyone else should avoid prolonged or strenuous exercise.

Michael Toole, regional air quality coordinator for the Idaho Department of Environment, told the Statesman that a red air quality advisory is likely, but that worse air quality sometimes cannot be ruled out.

“We could see hourly values ​​in purple,” Toole said. “The forecast itself is over a 24-hour period, so the way the air quality index and the forecast works is for particulate matter like smoke, we’re forecasting for the entire 24-hour period. So essentially we’re saying that this is what we expect it to average out to be over this 24-hour period.”