Fog, mist and haze[PDF]

Fog

Fog is ground level cloud reducing horizontal visibility to less than 1km.

Fog is a real danger for general aviation pilots, and can even be for one under certain conditions for commercial pilots.

Exemple : Fog banks are expected in the airport vicinity. During the IFR approach, VMC conditions are maintained, no fog patch in sight, manual approach is flown. Just above the threshold, at the beginning of the flare, the aircraft suddenly enters a fog patch. Visibility falls, it's to late to go around (due to inertia), but there is no visual reference to correctly flare the aircraft.

It consists of very small water droplets in suspension in the lower layer of the atmosphere. Depending on the temperature, the water may be frozen which would result in freezing fog.

For fog to form, a weak (<10kt) wind is required to keep water droplets/ice crystals in suspension. Absence or end of wind result gives dew or frost on the ground (common in the morning).

Fog symbol on charts is ≡

Mist

Mist is a phenomenon consisting of a large amount of water droplets/ice crystals present in a layer of the atmosphere. Relative humidity is generally between 60% and 100%.

Mist does not represent a real danger for commercial aviation pilots, visibility is between 1km and 5km).

Mist symbol on charts is =

Haze

Contrary to fog and mist, haze is a horizontal visibility reduction due to non-aqueous particles.

Humility of the air mass in less than 60%. Horizontal visibility less than 5km.

Particles can be dust, sand grains, pollen grains, chemical pollution, etc.

---

See also

• None

Reference

• None

Author

• VID 450012 - Creation