Definition
A type of fog composed of tiny ice crystals suspended in the air, forming when the air temperature is well below freezing (typically -10°C or colder) and water vapor sublimates directly into ice rather than condensing into liquid droplets. It commonly occurs in arctic and polar regions and produces a dense, sparkling haze that significantly reduces visibility.
Plain English
Fog made of tiny ice crystals instead of water droplets. It forms in very cold air, when it's so cold that the moisture skips the liquid stage and turns straight into ice in the air.
Context Anchor
Seen in cold-weather weather discussions, especially when planning taxi, takeoff, or landing at airports in very cold regions.
Derivation
Ice comes from the Old English word for frozen water; fog comes from a Danish term for mist or spray. Together they point to the crystalline rather than droplet composition.
Why Pilots Care
Ice fog can reduce visibility to near zero on runways and taxiways while also increasing the risk of carburetor or airframe icing.
Grounding Statement
Picture a very cold, calm morning where moisture in the air becomes tiny ice crystals hanging over the runway instead of staying as invisible vapor.
Intuition Check
Ice fog is not just ordinary fog that has frozen onto an airplane. It is fog made of ice crystals already floating in the air.
Example Sentence 1
The pilot delayed departure from Fairbanks when ice fog reduced visibility on the runway to less than a quarter mile.
Example Sentence 2
In the far north, ice fog often forms after sunset and can linger until the sun returns or winds pick up.