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Altostratus clouds are classified as:
  • A
    high level clouds.
  • B
    medium level clouds.
  • C
    low level clouds.
  • D
    convective clouds.

Refer to figure.

ALTOSTRATUS (AS) – are mid-level, gray or blue-gray clouds that usually cover the whole sky - giving a “ground glass” effect around the sun or moon. Usually composed of a mixture of water droplets and ice crystals.

  • Base normally between 6500 ft and 23 000 ft above ground level.

CLOUD HEIGHT BANDS

LOW LEVEL CLOUDS

BASES 0 ft – 6500 ft
WATER DROPLETS

STRATUS ST
STRATOCUMULUS SC
CUMULUS CU
CUMULONIMBOS CB
NIMBOSTRATUS NS – may also be classified as medium level.

Cumulus and cumulonimbus will, however, have significant vertical development and will extend from LOW to HIGH levels.
CB could extend into lower stratosphere.

MEDIUM LEVEL CLOUDS

BASES 6500 ft – 23000 ft

ALTOSTRATUS AS
ALTOCUMULUS AC
NIMBOSTRATUS NS

Characterised by prefix “Alto”

HIGH CLOUDS

BASES 16500 ft – 45 000 ft
ICE CRYSTALS

CIRROSTRATUS CS
CIRROCUMULOS CC
CIRRUS CI

Characterised by prefix “Cirro”.

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