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Trapped: Madison under the Clouds

Southern Wisconsin remains under a “Temperature Inversion” - meaning more clouds & fog tomorrow.
Warmer air aloft keeps cooler air and a layer of clouds trapped near the surface.
Warmer air aloft keeps cooler air and a layer of clouds trapped near the surface.(WMTV NBC15)
Published: Jan. 6, 2021 at 5:52 PM CST
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MADISON, Wis. (WMTV) - It’s been a gloomy, yet pretty last few mornings thanks to to the ice which has formed on trees & branches. But, why have the fog & clouds settled in? Why have we seen so little sunshine?

You can thank what we call a “Temperature Inversion”. It’s the meteorological term for increasing temperature with height.

Normally, the atmosphere gets progressively cooler with increasing height. However, this week, there’s been a change in the norm. Cooler air near the surface (from nighttime cooling and influence from the snow pack) has been trapped by a layer of warmer air aloft. It’s more common in Winter than during any other time of the year.

Wednesday morning’s surface temperatures hovered in the 20′s while temperatures a few thousand feet up were above freezing. This “inversion” creates a boundary which traps moisture near the surface. As the afternoon took hold, early morning fog dissipated and temperatures climbed into the upper 20′s - very near the temperatures several thousand feet up. Although the inversion was weaker during the day, a layer of clouds persisted - blocking out the sun.

After the sun sets, temperatures cool to the dew point - the temperature at which the air condenses out moisture. This has led to our repeated rounds of overnight and early morning fog - often freezing.

To get rid of the fog, clouds, and the inversion, a weather system or frontal boundary needs to clear the high-pressure and light winds. It looks like that will happen over the weekend as a cold front sweeps across southern Wisconsin. While not knocking out all the clouds, it should clear out low-level moisture - reducing chances for low clouds and fog.

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