frost point

noun
1.
the temperature of the air at which hoarfrost begins to form.
Examples from the web for frost point
  • Frost crystals form when water vapor freezes upon contact with a surface that is below the frost point.
  • Temperatures below the frost point are occasionally seen in the winter polar stratosphere.
  • Frost typically forms if the temperature on a given surface cools to the frost point.
Encyclopedia Article for frost point

temperature, below 0 C (32 F), at which moisture in the air will condense as a layer of frost on any exposed surface. The frost point is analogous to the dew point, the temperature at which the water condenses in liquid form; both the frost point and the dew point depend upon the relative humidity of the air

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