The air in the Treasure Valley is still expected to improve this weekend, but it took a dramatic turn for the worse Friday afternoon in Boise, earning a Department of Environmental Quality rating of very unhealthy (purple) for several hours, said Michael Toole, airshed coordinator for Idaho DEQ.
The agency had forecast Friday air quality two levels better than that — orange, or unhealthy for sensitive groups, an improvement from the red ratings that dominated most of this week because of smoke from the Walker Fire near Idaho City.
The DEQ’s Michael Toole said the worsening of Boise’s air “caught us a little off-guard,” but a strengthened inversion and continued smoke from the forest fire combined for the lowest air quality in recent memory.
“In the 15 years I’ve been here I have not seen a purple hourly reading on these meters,” Toole said.
Those readings prevailed on hourly averages from 11 a.m. to 2 p.m., but at 3 p.m. there was slight improvement to red.
While Boise air rated purple, Meridian readings came in as orange and those in Nampa were at yellow, Toole said.
“For most of the Valley, that forecast we issued for orange is going to hold very true,” he said.
Hopes for improved air quality over the weekend remain in place, he said, because of cooler temperatures and possible rain Saturday and Sunday. The National Weather Service has said that rainfall is likely Saturday evening and Sunday.
The air quality forecast is for orange on Saturday, and Toole said the forecasts will likely be more optimistic for Sunday and beyond. The forecast estimates overall air quality, so a smoky haze is quite likely, particularly in the Boise area, DEQ said. Hourly levels therefore still could hit red on Saturday.