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Meteorology
3.6.2.2 Alto – middle-level clouds
These clouds form between 6500 and 23000 feet but can extend higher. They
consist of both water droplets and ice crystals.
• AC = Altocumulus
o Small supercooled water droplets. Ice crystals below -10°C.
o Normally does not produce precipitation.
o Often shows color variations at the cloud edges.
• AS = Altostratus
o Small water droplets and ice crystals.
o Large horizontal and vertical development.
o Associated with fronts, precipitation begins from AS.
o Persistent rain or snow.
3.6.2.3 Cirro – high-level clouds
These clouds are found high in the atmosphere, above 16500 to 45000 feet,
where the temperature is very low.
They can extend very high in the atmosphere and consist mainly of ice crystals.
• Ci = Cirrus
o Ice crystals.
o No precipitation.
o Signals bad weather within 18-36 hours.
• CS = Cirrostratus
o Ice crystals.
o No precipitation.
o Forms when warm air rises over colder air.
o Signals worsening weather with falling air pressure.
• CC = Cirrocumulus
o Ice crystals.
o No precipitation.
o During formation, it consists of small, heavily supercooled droplets.
o In summer, signals thunderstorms in the afternoon or evening.
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 279
