How long Utah's smoggy and foggy weather is expected to last

SALT LAKE CITY — Utah's capital looked almost apocalyptic Monday as the tops of its tallest buildings were barely visible from the city sidewalks, not all of which is related to an ongoing inversion event worsening air quality across Wasatch Front and northern Utah.

The inversion has cooled temperatures enough that fog has descended into many Utah communities over the past few days, which has worsened visibility, particularly between evenings and mid-morning, said Jon Wilson, a meteorologist with the National Weather Service. The fog blends into the haziness in the sky.

"It's really both," he explained to KSL.com Monday. "You're essentially seeing everything that's literally getting put into the atmosphere. You're seeing the fog, which is being formed naturally from the moisture in the low levels but you're also seeing car exhaust, emissions from plants — it's everything that gets put into it."

The latest inversion

Utah's latest temperature inversions began late last week, following a few days of stormy activity. These events tend to form after a storm, when the air on the valley ground is cooler than higher up in the atmosphere, as noted by the Utah Department of Environmental Quality.

For example, the temperature in Alta, at a location near 9,000 feet, reached 42 degrees Monday morning, while the temperature at Salt Lake City International Airport, located 4,500 feet below in elevation, remained at 28 degrees, KSL meteorologist Matt Johnson said.

Haze develops as pollution from the valley gets trapped in the temperature inversion layer, causing air quality to plummet. Salt Lake City's air quality was rated as the 22nd worst among 110 cities in the world that IQAir tracks, as of Monday afternoon.

What's behind the fog?

The lower valley temperatures have also resulted in dense fog building up, worsening visibility in parts of the region. This tends to happen after a long inversion event, Johnson explained. Water vapor from the soil, snowmelt and the Great Salt Lake build up in the atmosphere, leading to fog.

Wilson adds that, in some cases, it's cold enough that snow-like conditions emerge in areas like bridges and overpasses.

"With that inversion, there's just enough moisture near the surface that what you're getting is that moisture condensing and because it's below freezing, like it has been the last few mornings, that's causing the fog to form what we call freezing fog," he said. "It almost looks like it's lightly snowing, but it's not."

How long will it last?

This trend of fog and smog is expected to last at least another day, according to Wilson. It's unclear how long the fog conditions will build up beyond Monday night or Tuesday morning because this is harder to forecast. Inversion conditions, however, are expected to linger through at least Friday.

The Utah Division of Air Quality forecast lists Salt Lake and Davis counties as having air quality levels reach orange, or levels that are unhealthy for sensitive groups, through at least Tuesday. Moderate air quality levels are forecast across the Wasatch Front, as well as northern and eastern Utah through at least Wednesday.

A storm system off the Pacific Coast is producing cloud cover in Utah, but a high-pressure system over the state is blocking it from clearing out the inversion, he said. A storm system is expected to arrive this weekend, to knock the bad air out and provide more snow, but there is also some "uncertainty" about that, too.

"Not all models are saying yes on that," Johnson said.

So, poor air quality — and possibly visibility — are expected to be mainstays this week. Full seven-day forecasts for areas across Utah can be found online at the KSL Weather Center.

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