Play Live Radio
Next Up:
0:00 0:00
Available On Air Stations

What’s a Utah inversion and why is the air so icky?

The silhouette of Utah State Capitol is shown against the blue sky and particulates from an inversion Wednesday, Jan. 2, 2013, in Salt Lake City.
Rick Bowmer
The silhouette of Utah State Capitol is shown against the blue sky and particulates from an inversion Wednesday, Jan. 2, 2013, in Salt Lake City.

When there’s snow on the ground and smog in the air, it’s probably an inversion.

Winters aren’t the same as they were a decade ago. Blankets of snow used to cover the ground over a foot thick, and northern Utahns were able to build snow forts and snowmen and sled wherever there was a hint of a hill. But there have always been inversions. While the sparkling snow covers the mountain peaks, in the valley there is a smoggy blanket obscuring the city.

Inversions are typical during Utah winters. An inversion is a meteorological condition that is created when warmer air settles on top of a valley and traps colder air. Mountains surround the Salt Lake Valley, and other valleys throughout the state, which hold everything in place.

“What that does is keeps all the pollution and emissions and colder air under this cap, kind of like a lid,” said Bo Call, manager of the air monitoring section for the Utah Division of Air Quality.

Colder temperatures and snow exacerbate the condition.

Snow cover on the ground is often the catalyst that triggers the inversion, said Jon Meyer, an assistant state climatologist from the Utah Climate Center. When there is high pressure in the valley, snow stays in lower elevations. That snow reflects daytime sunshine and keeps the valley cool.

“All of those ingredients together allow cold air to pool in the middle of the valleys in the low elevations, and we get these temperature inversions that trap the air in the valleys,” Meyer said.

Inversion season usually starts in November and goes until the end of March. January and February, Meyer said, are the core inversion months because of the short days, long nights and increased snow cover chances.

However, over the last couple of decades, snow remains on the ground for a shorter and shorter period of time. Meyer said warming temperatures across the globe have caused the snow season to arrive later and end earlier, which makes the inversion season shorter as well.

While forecasting what the inversion season will look like is tough, Meyer said they can make some predictions.

“What we can do is connect the dots from some of the ingredients that go into the recipe of inversions,” Meyer said.

This year, like the last two years, wintertime will have the background of La Niña ocean surface temperature cooling in the central and east-central Pacific. It usually occurs around every three to five years, but will sometimes happen for several years in a row, like it has the last three years.

During La Niña, Meyer said the Southwestern U.S. tends to dry out so there aren’t as many snow storms. Temperatures are also above average. Since La Niña conditions are occurring again this year, the inversion season is likely to be similar to the last two years.

Air quality is also tied to inversions.

“The fascinating thing about inversions is it really visualizes the amount of pollution that leaves our surface on any given day,” Meyer said.

Since the pollution can’t spread into the full atmosphere, inversions cause the pollution to collect in a much smaller area right near the surface of the ground. This can have negative effects on people with respiratory conditions, but it depends on the person.

“For some people, this is just going to be an irritant,” said Bo Call. “But for others that are more sensitive, they can get into a bit of distress.”

People can also get away from inversions by staying indoors or going up into the mountains above the inversion. When someone needs to go outside, Call said they can look at the app Utah Air. It uses data to measure what the air is like in the area.

Kristine Weller is a newsroom intern at KUER. She’s only been a journalist for a year but is excited to see what the future holds.
KUER is listener-supported public radio. Support this work by making a donation today.