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Rime Ice and Hoar Frost

Rime ice occurs when liquid droplets from fog freeze when they make contact with trees or other objects. The water droplets go from a gas state to a solid state with no melting in between.

Hoar frost is a deposit of interlocking ice crystals (hoar crystals) that form on objects that are exposed to the air, such as tree branches, plant stems and leaf edges, wires, poles, etc. Frost is not frozen dew.

Oelwein, Iowa

Possible Guiding, Compelling and/or Anchoring Questions

  • What weather conditions allow for different types of precipitation to occur, including hoar frost, rime frost, sleet, hail, fog and snow?
  • What forms of precipitation go through the process of sublimation?
  • What is the difference between hoar frost and soft rime ice?

Classroom Suggestions

  • If condensation or sublimation of the water vapor occurs directly at or near to the surface of the Earth, it is the deposited precipitation such as dew or hoar frost.
  • Research the weather conditions at the location and time this photo was taken.
  • Lab: Create rime ice.

Related Resources


Iowa Core Alignment

Earth and Space Science
Disciplinary Core Idea
ESS2: Earth’s Systems

Credit Info

Submitted by Jill Kelly.


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