Inversions likely to plague Wasatch Front for most of week

As chilly temperatures mark the start of Utah’s holiday season, they also bring an unwelcome visitor to the state’s northern valleys — inversions and the dirty air trapped inside them.

A thin haze already sat within Salt Lake City’s skyline Monday, and it’s likely only going to get denser over the next few days.

“We’re getting into that time of year, climatologically,” said Hayden Mahan, a Salt Lake City meteorologist with the National Weather Service. “Late November through mid- to late February is sort of our quote-unquote inversion season.”

He said the smoggy conditions come when temperatures drop at night and cold, dense air funnels into the bottoms of valleys, stagnating like cold water trapped at the bottom of a filled sink.

“Areas at higher elevations will end up getting warmer typically throughout the day, while the cold air sort of just stays in place at the bottom of the valley,” Mahan said.

Then, as that trapped air stays longer and longer, it becomes more and more polluted and unhealthy for certain populations to breathe, especially in urban areas.

The Utah Department of Environmental Quality’s three-day air quality forecast showed Salt Lake and Davis counties’ air quality is likely to be “unhealthy for sensitive groups” on Tuesday and Wednesday.

In those and several other counties, there are mandatory prohibitions on open burning and solid-fuel burning.

According to Mahon, things could be worse. One silver lining: a lack of snowpack.

“That can make it worse, because it kind of exacerbates that cold pool on the ground,” he said. “That would just strengthen your inversion, and that can also provide some moisture to develop some fog or some low clouds.”

There also is hope that storm systems near the end of the week could clear or at least partially alleviate the pooled air.

“We’ve got some high pressure building off to our west, and we might get a little bit of a reprieve on Friday,” Mahan said. “We have a weak storm that’s going to be passing by to our east.”

He is doubtful that will entirely deliver those in Utah’s chilly valleys from their trapped and dirty air, but a larger storm late this weekend could.

“There’s still quite a bit uncertainty,” Mahan specified. “There’s basically a minority of our model guidance that has a storm on Sunday.”

If that storm doesn’t come, the inversions could continue to stick around.