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Hoar Frost
From SKYbrary Wiki
| Article Information | ||
|---|---|---|
| Category: | Weather | 
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| Content source: | SKYbrary | 
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| Content control: | EUROCONTROL | 
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| WX | |
|---|---|
| Tag(s) | Weather Phenomena Icing |
Description
Hoar frost occurs when a sub-zero surface comes into contact with moist air. The water vapour turns directly into ice by sublimation forming a white crystalline ice coating which can normally be brushed off. Hoar frost will form in clear air when an aircraft has been parked overnight in sub-zero temperatures and will form when an aircraft flies from sub-zero temperature air into warm moist air, such as in descent or climbing through a temperature inversion layer. Hoar frost is not as dangerous as clear ice but may affect the lift characteristics of the wings. Frost remaining on the wings at take-off is especially dangerous.
Further Reading
For information on other types of icing, the hazards associated with icing, the types of cloud that may be associated with icing, and solutions, see the main articles on icing and Cloud Types.