Ask Storm Team 11: How does frost form?


Thursday’s Ask Storm Team 11 question was, “How does frost form?”

Frost typically occurs when temperatures fall below 36F degrees. 

When the temperature is cooled to the dewpoint temperature, condensation occurs and water comes out of the atmosphere as dew or frost.

But temperature isn’t the only factor in the formation of frost. 

You also need clear skies. This allows for radiational cooling to occur at the surface.

Calm winds are needed as well to prevent any mixing of the atmosphere. 

How does frost form when temperatures are above freezing? Keep in mind, temperature changes with height too. Although the temperature at a weather station, which is typically 4-5 feet above the surface, is about 36F degrees, at the very surface it may be 30F degrees. 

Here are some general guidelines from the NWS on temperature and frost coverage:

  • 38F – 42F: patchy frost
  • 33F – 37F: areas of frost 
  • 32F and below: widespread frost/freeze

Other factors such as topography, soil moisture, and stage of vegetation all affect the development of frost.

Ask Storm Team 11 your questions!

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