As we inch closer to the coldest weather of the season, now is as a good a time as any to talk about frost.
Frost is ice that forms on a surface that has a temperature less than, or equal to 32°F. It occurs best in cold, clear and calm evenings.
Why? Well, when we're talking about frost forming on grass, when there is no wind to mix the atmosphere cold air sinks. Through radiational cooling, any heat, or energy from the grass that was provided during the day, is pulled into the atmosphere ultimately cooling it below freezing. Any moisture in the air will freeze on contact to the grass, thus giving us frost.
Air temperature does not necessarily have to be below freezing for a frost to occur. Remember, cold air sinks. Accurate thermometers are placed 5 feet above the ground to get an accurate measurement, without the heat, or lack thereof another surface interfering with the actual air temperature.
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