The temperature inversion in the Great Salt Lake area, more commonly referred to as the inversion by locals, is typically at its worst in January and February, when the air is cold, there is snow on the ground, and the wind is still.
It happens when a high-pressure system hovers over the Wasatch Mountains and compresses cold air down upon the valley, where pollutants from automobile fumes and fireplaces are produced. When combined with these pollutant, the area fog (which forms from ice crystals in the cold air) becomes smog and takes on a brownish hue. Often the amount of pollutants in the air exceeds the EPA's health standard.
On windless days, this mixture is denser than the warmer air layer above it and thus cannot escape.
So what results is a cold layer of smog under a warmer layer of air.
When this occurs, the smog crystals fall out of the air throughout the day, clinging to
objects and producing hoarfrost. At times, it appears to be snowing. But unlike real snow, this stuff leaves a residue.
Having snow on the ground can make things worse, because the whiteness reflects heat back up into the sky, instead of absorbing it and warming the ground.
A good snowstorm or strong wind is what is needed to restore the balance.
Usually the higher you go into the mountains, the colder the air, but during the temperature inversion, this is not the case. Conditions can be such that the valley is around ten degrees (Fahrenehit) and blanketed with a cream soup fog, while the mountain temperature is thirty-five degrees (Fahrenehit) with sunny skies. So an easy way to get a little relief from the smog and cold air is to drive up one of the canyons. Looking down into the valley from up above, the inversion looks like a layer of fluffy clouds.