Utahns who are sensitive to smog should stay indoors, and motorists were advised to reduce trips or take public transit on Friday as air pollution worsened along the Wasatch Front.

According to the Utah Department of Environmental Quality, Cache County’s PM 2.5 (fine particulate) level was at orange — “unhealthy for sensitive groups” — while Salt Lake County’s level dropped from orange to yellow, or “moderate,” as of 7 a.m. Friday. Davis, Utah and Weber counties also were at “moderate” pollution. Burn restrictions were in effect throughout northern Utah.

The Salt Lake City International Airport also delayed and canceled several flights, according to a tweet Friday evening, because of the low visibility from the inversion.

Conditions are unlikely to improve for at least another day or two, the National Weather Service reported.

“Persistent temperature inversions across northern Utah valleys will result in degraded air quality and patchy fog through Saturday,” a Friday weather bulletin stated.

A storm is expected to bring rain and snow to the western two-thirds of Utah starting late on Saturday and could bring some relief from the air pollution. Look for a 70 percent chance of rain in Salt Lake City and Provo on Sunday, possibly turning to snow on Sunday night, with an 80 percent chance of precipitation in Ogden and Logan. Snow accumulation is likely in the mountains.

A small storm on Thursday did little to clear the air, which returned to “orange” levels of pollution by about 7 p.m. along the Wasatch Front. But it did provide a small boost to Utah’s ski resorts, with 6 inches of snow falling at Snowbasin, 5 inches on Brighton’s crest, 4 inches at Alta and Powder Mountain, and 3 inches at Solitude, Snowbird and Park City.