US Trends

what is freezing fog

Freezing fog is a type of fog that occurs when tiny liquid water droplets are suspended in the air while the air temperature at ground level is at or below freezing, so those droplets can freeze on contact with surfaces.

What freezing fog is

  • Fog itself is simply a low cloud made of tiny liquid water droplets close to the ground, formed when air becomes saturated as it cools or gains moisture.
  • In freezing fog, the air temperature is at or below 0°C (32°F), but the droplets are “supercooled” – still liquid despite being below freezing.
  • When these droplets touch surfaces at or below freezing, they freeze into a thin coating of ice called rime, often giving trees, signs, and other objects a white, feathery look.

How it forms

  • It usually develops on cold, calm, clear nights when the ground loses heat, cooling the air near the surface until it reaches saturation and fog forms.
  • If that fog forms while temperatures are below freezing, the droplets stay supercooled and become freezing fog, typically in a temperature range roughly between 0°C and about −20°C.
  • Meteorological reports label freezing fog as “FZFG” in aviation weather observations (METARs).

Why it’s hazardous

  • Like normal fog, it sharply reduces visibility, which can lead to dangerous driving conditions and travel delays.
  • Moisture from the fog can freeze on roads, bridges, and walkways, creating black ice that is difficult to see but extremely slippery.
  • Ice can also build on trees, power lines, and aircraft, sometimes causing damage or requiring de-icing before flights.

Quick safety tips

  • Slow down, increase following distance, and avoid sudden braking or sharp turns when freezing fog is in the forecast.
  • Use low-beam headlights (not high beams) in fog, and be prepared for hidden icy patches, especially on bridges and overpasses.
  • If travel is optional during a freezing fog advisory, waiting for conditions to improve is often the safest choice.

In short, freezing fog is regular fog happening in sub-freezing air, with the added twist that those invisible droplets can freeze on contact and turn surfaces into an icy hazard.

Information gathered from public forums or data available on the internet and portrayed here.