Freezing fog is a type of fog that occurs when air temperatures are at or below freezing, and the fog is made of tiny liquid water droplets that are “supercooled.” These droplets can freeze instantly when they touch surfaces that are at or below 0°C (32°F), creating a coating of ice.
How it forms
Freezing fog forms like regular fog: moist air near the ground cools until the water vapor condenses into tiny droplets, creating a low cloud that reduces visibility. When this happens in subfreezing temperatures, the droplets remain liquid but are unstable and ready to freeze on contact with cold surfaces.
Effects and hazards
When the supercooled droplets hit roads, sidewalks, trees, power lines, or vehicles, they can form a thin, often hard-to-see layer of ice, including black ice on roadways. This can make driving and walking very hazardous and may also lead to ice buildup on structures, vegetation, and aircraft, sometimes producing rime ice with a white, feathery appearance.
