A high pressure system was to roll into the region late Wednesday, bringing with it a return of pollution-trapping air inversions and colder temperatures to northern Utah's urban valleys.
On Tuesday, the Utah Division of Air Quality rated the entire state as "green," or healthy for breathability. That was forecast to deteriorate considerably by late Wednesday or Thursday, though, when Salt Lake, Davis, Utah, Weber and Cache counties were down to "yellow," or moderate for air quality.
DAQ officials said that diminished air quality was likely to continue into the weekend as smog levels grew.
Colder temperatures, too, were to hit the state, despite generally sunny skies into late this week.