"Most of the smoke we are getting is coming from fires in western Nevada, northern California, southern Oregon and southern Idaho," said Seaman, "Winds are transporting the smoke east into northern Utah, which has been the case the past few days. An area of high pressure is going to build overhead and deflect some of the smoke north. Conditions may improve a bit, but I don't think we'll sweep the smoke out entirely until sometime the middle of next week."
In northern Utah, the smoke is pervasive.
The Bonneville Salt Flats are normally a place where clear, blue skies prevail during events such as Speed Week, which ends Friday. But on Wednesday, smoke and haze cast an unfamiliar and eerie light on the Flats and the dozens of racers still trying to set land speed records.
The good news, according to Bo Call, of the Utah Division of Air Quality's air monitoring section, is that while the air might look bad, it hasn't reached the point where the agency has had to issue a red-air quality alert, the most severe. On Thursday, air quality was rated "moderate" or yellow for Salt Lake, Davis, Utah, Weber, Box Elder, Tooele and Uintah counties. A moderate rating means the air is unhealthy for sensitive groups such as people with lung disease, children, elderly and people who are active outdoors.
"What you are seeing is particulate [pollution]," said Call. "This is normally a wintertime problem with inversions."
When the particulate pollutants reach 35 micograms per cubic meter, a red-air quality alert is issued. Such alerts are based on a 24-hour average, or an eight-hour average for ozone. The particulate number has been rising steadily this week, hitting 27.4 in Salt Lake City on Thursday.
"It can look worse than the numbers indicate from our monitoring," said Call. "In the case of the fires we've had, in most cases, it looks worse than the data actually indicates is the case."
Even so, Call said that people who run, bicycle or work outdoors can often feel the effects of smoke in the air.
Seaman said high pressure will keep the smoke stable until there is a transition to a more southwesterly flow that will be enough to sweep out the smoke.
"Until then, we're stuck with the hazy conditions," he said. "It looks like they could last until the middle of next week, around Wednesday. That is six or seven days out, but things could change. The high pressure is good news, because it will shift the smoke to the north. We won't be adding any smoke to the area."
Salt Lake area temperatures are expected to reach into the 90s most of the weekend with lows dropping to the mid-60s. In St. George, highs are expected to reach the low 100s, with lows dropping to the mid-70s.