SALT LAKE CITY (ABC4) – While Mother Nature still can’t decide if Utah should feel like Autumn or Winter, the one consistent season we’ve entered in Northern Utah is inversion season. Inversions are the strongest in Utah from December to February, but conditions can show up as early as November and as late as March. It’s the time of year we see inversion conditions take over, and in many of our valleys we see air quality decline as result. Prolonged inversion periods lead to an increase in particulate matter and that leads to high levels of fine particulate pollution. As that particulate matter rises, the ABC 4 Weather team alerts you to those changes. You will see graphics and maps like this giving you the current and forecast air quality conditions.

How does this happen? Well, an inversion occurs when our normal atmospheric conditions become inverted. Typically, temperature decreases with height, but when an inversion occurs temperature increases with height, and we have a dense layer of cold air trapped on the valley floor and a warmer layer above it. Our warm layer then traps pollutants within the cold layer and our air quality declines. Valley floor pollution becomes visible as haze first, then smog and no one particularly enjoys breathing that in.

High pressure allows for building inversions because as a high moves in, the gradual sinking of the warmer air acts as a cap over the cooler air, so we get a capping layer that appears liek the lid of a Tupperware. While we tend see periods of inversion building underneath areas of high pressure, that’s not the only ingredient for building haze. We also have light winds which reduce the mixing of cold and warm air, clear skies which increases the rate of cooling near the surface, longer nights which means the ground stays cooler longer and the sun angle. When the sun is lower on the horizon, it supplies less warmth to the ground and more warmth to the atmosphere and we see our benches and higher elevations warm up as a result. Areas with snow on the ground will also see inversion conditions set up more quickly, as snow on the ground enhances colder temperatures at the surface.

Nothern Utah’s topography also provides an ideal set up for strengthening inversions. The Salt Lake valley, and other valleys Cache Valley, the Uinta Basin and even in Cedar CIty, allow for those pollutants to settle close to the ground. For example, the Salt Lake Valley is surrounded by the Wasatch Mountains, Oquirrh Mountains and Traverse Mountains, so there really is nowhere for pollutants from vehicles and industrial areas to escape.

An active storm pattern is our friend this time of year, as passing systems promote mixing and moisture helps clean out pollutants. A strong storm offers relief and the clear skies and clean air we know and love.

To stay on top of our air quality, inversions and storm pattern, stay with Utah’s Most Accurate Forecast. You can follow along with us both on-air and online.

For more information on air quality in Utah and current air quality, click here.