Why Was There Ice If We Weren’t Below Freezing?

This is a good question from Steve noticing we weren’t officially below freezing Wednesday or Tuesday throughout much of Southeast Texas, but we did have a lot of frost on the ground and ice on the cars. 

Official temperature readings are taken 6 feet up so that things that occur on “ground surfaces, or any surface” doesn’t affect the outside temperature.  A car that has any moisture on the windows or roof will get what’s called evaporational cooling.  Evaporational cooling is similar to perspiration. When you work out your body sweats to cool itself. Moisture being evaporated will make a surface colder.  The air temperature may have been 37 degrees this morning, but grass or a car with moisture would have been below 32 degrees. Factors such as these are why it’s colder on surfaces than the surrounding air on a morning like this.

This is also a good example why official temperature reading are taken 6 feet in the air, away from tall buildings, with grass surrounding the weather station.  Most temperature records go back to the late 1800s, and accuracy is key to monitor how our environment is changing or not changing.  Imagine if a temperature gauge was near I-10 in the summer, we would set a high temperature record every day the sun is out. 

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One Response

  1. Thanks Anthony, I knew I was asking the right person. I never would have thought of the evaporative cooling effect.

    Sorry I missed thr broadcast this morning… you’re the best.

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