What is Frost?

Most of the area saw their first frost on Saturday morning as temps fell to near freezing away from Lake Michigan. There are a lot of misnomers about what exactly creates frost.

Frost is not frozen dew. Dew occurs when the temperature at the surface cools to the dew point and condensation occurs. Frost is actually created as water vapor freezes on objects. This is called deposition. Frost normally occurs on clear nights and happens on roofs, cars, grass, and other plants. Temperature sensitive plants can die if a frost occurs.

Another question I always hear is, “how can you get frost when the temperature is above freezing?” The official height of a thermometer is 5.5 feet above a grassy surface. On a clear and calm night, the closer you get to the earth’s surface the colder it gets. At 5.5 feet the temperature can be five degrees warmer than at the surface. This is why frost can occur even when the temperature at the height of the thermometer is above freezing.

Mark Baden


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