Page 287 - PPL-engelsk 2025

Meteorology

In order to be called fog, the humidity in the air must reduce visibility to less

than 1000 meters. If visibility is reduced to between 1 and 10 kilometers

(without precipitation), it is called mist.

When fog is present, it is indicated in weather reports as FG (for "Fog").

Fog can form in various ways, such as:

- Radiation fog

- Advection fog

- Orographic fog

- Front fog

- Rime fog

- Sea smoke

3.6.6.1 Radiation fog

Radiation fog often forms at night or early in the morning over land when the

ground quickly loses heat to space (radiation), and the nearest layer of air cools
to the dew point.

Wind will be 1-5 knots (for distribution of fog, no wind = dew or rime).

A. In the afternoon, the ground's heat radiation becomes greater than

incoming radiation.

If turbulence is weak, the constant temperature decrease with height

cannot be maintained.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 287