The 27 meteorological states of the sky from the World Meteorological Organization Manual of Codes (Number 306, Volume I Part A, Codes 0513, 0515, and 0509)

L1 - Cumulus humilis or Cumulus fractus other than of bad weather, or both

L2 - Cumulus mediorcris or congestus, with or without Cumulus of species fractus or humilis or Stratocumulus, all having their bases at the same level

L3 - Cumulonimbus calvus, with or without Cumulus, Stratocumulus, or Stratus

L4 - Stratocumulus cumulogenitus

L5 - Stratocumulus other than Stratocumulus cumulogenitus

L6 - Stratus nebulosus or Stratus fractus other than of bad weather, or both

L7 - Stratus fractus or Cumulus fractus of bad weather, or both (pannus), usually both Altostratus or Nimbostratus

L8 - Cumulus and Stratocumulus other than Stratocumulus cumulogenitus, with bases at different levels

L9 - Cumulonimbus capillatus (often with an anvil), with or without Cumulonimbus calvue, Cumulus, Stratocumulus, Stratus or pannus

M1 - Altostratus translucidus

M2 - Altostratus opacus or Nimbostratus

M3 - Altocumulus translucidus at a single level

M4 - Patches (often lenticular) of Altocumulus translucidus, continually changing and occurring at one or more levels

M5 - Altocumulus translucidus in bands, or one or more layers of Altocumulus translucidus or opacus, progressively invading the sky; these Altocumulus clouds generally thicken as a whole

M6 - Altocumulus cumulogenitus (or cumulonimbogenitus)

M7 - Altocumulus translucidus or opacus in two or more layers, or Altocumulus opacus in a single layer, not progressively invading the sky, or Altocumulus with Altostratus or Nimbostratus

M8 - Altocumulus castellanus or floccus

M9 - Altocumulus of a chaotic sky, generally at several layers

H1 - Cirrus fibratus, sometimes uncinus, not progressively invading the sky

H2 - Cirrus spissatus, in patches or entangled sheaves, which usually do not increase and sometimes seem to be the remains of the upper part of a Cumulonimbus; or Cirrus castellanus or floccus

H3 - Cirrus spissatus cumulonimbogentius

H4 - Cirrus uncinus or fibratus, or both, progressively invading the sky; they generally thicken as a whole

H5 - Cirrus (often in bands) and Cirrostratus or Cirrostratus alone, progressively invading the sky; they generally thicken as a whole, but the continuous veil does not reach 45 degress above the horizon

H6 - Cirrus (often in bands) and Cirrostratus or Cirrostratus alone, progressively invading the sky; they generally thicken as a whole, but the continuous veil extends more than 45 degress above the horizon, without the sky being totally covered

H7 - Cirrostratus covering the whole sky

H8 - Cirrostratus not progressively invading the sky and not entirely covering it

H9 - Cirrocumulus alone, or Cirrocumulus predominant among the cirriform clouds