Frost


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Note: "freezing occurs when the temperature of air falls below the freezing point of water (0 °C, 32 °F, 273.15 K). This is usually measured at the height of 1.2 m above the ground surface.

There is a rather subjective scale to show several degrees of frost severity:

slight frost: 0 to −3.5 °C (32.0 to 25.7 °F)moderate frost: −3.6 to −6.5 °C (25.6 to 20.3 °F)severe frost: −6.6 to −11.5 °C (20.2 to 11.3 °F)very severe frost: below −11.5 °C (11.3 °F)A temperature at or below freezing is not necessary to get ground frost or hoar frost; they can form even if air temperature is above freezing point if the sky is clear. This is because the ground loses heat due to radiation. It radiates its heat to the sky/space. When you "feel" a very cold surface, it is because you are radiating your heat to that cold surface, the cold surface becomes warmer, and you become colder. The amount of heat that radiates is proportional to the difference in temperature between the two objects. At night, the atmosphere is not being warmed by the sun and the sky/space can approach absolute zero (-469 degrees F, -273 degrees Celsius). On a clear night the ground can become colder than the air because it radiates its heat to the sky, and frost can form." - (en.wikipedia.org 20.06.2020)

[Last update: 2020/06/20]