Inversion
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Hi, I'm Bryan Yeaton and this is the Weather Notebook.

Earlier this year, visitors to the Winter Olympics in Salt Lake City got a glimpse of more than just glistening gold medals. They experienced one of the city's most common weather phenomena--a temperature inversion that pulls down a blanket of dense smog over the area. Correspondent Jeff Rice explains why inversions occur there.

Inversions can occur almost anywhere, but tend to be worse in areas like the Salt Lake Valley, which is surrounded by mountains. The mountains shield the wind, and the fog and pollution remain cupped like the foam of a cappucino.

The smog blocks out the sun, and the air quality, filled with the exhaust of half a million cars, gets downright toxic.

Then locals like National Weather Service meteorolgist Larry Dunn know it's time to head to the mountains to catch some rays above the cloud layer.

LD: When we have a temperature inversion. It's very depressing. Just day after day, you'll just break right out of it into blue sky, sunny conditions, and actually above normal conditions. In fact, it's that warm air up there that's trapping the cold air down here.

The cold air is denser and heavier, so it stays close to the ground. Then , until the wind picks up, it's like closing all the doors and windows and sitting inside with the car running... And it's not just about cold air. Inversions are common in both winter And summer. Even at 80 or even 90 degrees, variable temperature layers can trap cities in a haze of fog and smog.

Correspondent Jeff Rice lives in Boise, Idaho. The Weather Notebook is a production of the Mount Washington Observatory. The program is supported in part by the National Science Foundation and Subaru of America. For more on inversions, go to our website at weathernotebook. org.