Page 276 - PPL-engelsk 2025
P. 276
Meteorology
3.6 Clouds
One of the worst conditions for the VFR pilot is the humidity in the air. It
reduces visibility, and one may be forced to fly at low altitude to remain below
clouds. This increases the risk of getting close to obstacles – maybe too close!
If there is a forecast for poor visibility, turn around – do not continue into
something uncertain!
3.6.1 Formation of clouds
When air is lifted, it cools down. The invisible water vapor condenses, and when
the humidity reaches 100%, some of the water vapor will condense into clouds.
A cloud is a collection of very fine water droplets that condense around
microscopic dust particles small enough to stay floating. If several water
droplets merge into larger ones, they can fall as rain.
If condensation occurs at temperatures below freezing, the water vapor may
sublimate into ice crystals, forming wispy clouds.
Much rain starts as ice crystals in the upper layers of the atmosphere, and if it
is cold enough, they can reach the ground as snow. At higher temperatures,
they melt on the way down and merge with the water droplets of lower clouds.
A form between snow and rain is hail, which forms when melting ice crystals
and water droplets are lifted by updrafts to temperatures below freezing,
where they freeze into ice.
3.6.1.1 Condensation level
All cloud formation and potential precipitation occur because the air
temperature is lowered below the dew point. This typically happens when the
air rises for some reason.
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 276
