Weather Whys; Inversion

This is weather wise. An inversion occurs when the air near the ground is colder than the air above it. That's considered a stable situation because cold air is denser than warm air and so it doesn't tend to rise as easily. Therefore, if an inversion occurs over a city, all of the pollutants produced by the town will essentially be trapped there. That can create dangerously poor air quality and people with respiratory and heart problems can experience serious difficulties. Some cities like Los Angeles and Denver are notorious for having persistent inversions and frequent air pollution problems. There are several atmospheric conditions necessary for an inversion to develop. One of the most important is a lack of wind. If there's a good breeze, the warmer air above gets mixed with the colder air below, basically evening out the temperatures and preventing development. Clear skies help spur on an inversion.

A thick deck of clouds or even high humidity can act as an insulating blanket, keeping a lot of the earth's heat from escaping. That keeps the surface relatively warm and works against an inversion. Inversions can be tricky. The temperature can vary quite a bit over just a few feet. A thermometer hanging at eye level may give the reassuring news that the temperature is still a few degrees above freezing, but next to the ground where the plants live, it can be an entirely different story. We'd like to know what you think of Weatherwise. Please write us at Weatherwise, K-G-O-U radio, the University of Oklahoma, Norman, 73019-025-0. Weatherwise is made possible with the assistance of the National Weather Service Forecast Office on the National Severe Storms Laboratory, both in Norman, Oklahoma. For Weatherwise, I'm Drew Marlon.