Middle Cloud Classifications
The following
schematic is in pdf format. If you are using Netscape 3.0, the file will automatically
load for you for viewing and printing if you've installed Acrobat Reader as
a plug-in.
If needed, you can download Acrobat Reader for free here.
• Middle Clouds:
Altocumulus, Altostratus, and Nimbostratus
1
1 is the highest priority and 11 is the lowest priority in designating CM
if more than one type is present.
CM
Code
Priority1
Nontechnical
Cloud Type Description
0
11
No Altocumulus,
Altostratus or Nimbostratus
1
1
Altostratus,
the greater part of which is semi-transparent; through this part the sun
or moon may be weakly visible, as through ground glass.
2
2
Altostratus,
the greater part of which is sufficiently dense to hide the sun or moon,
or Nimbostratus.
3
102
Altocumulus,
the greater part of which is semi-transparent; the various elements of
the cloud change only slowly and are all at a single level.
4
8
Patches
(often in the form of almonds or fishes) of Altocumulus, the greater part
of which is semi-transparent; the clouds occur at one or more levels and
the elements are continually changing in appearance.
5
7
Semi-transparent
Altocumulus in bands, or Altocumulus in one or more fairly continuous
layers (semi-transparent or opaque), progressively invading the sky; these
altocumulous clouds generally thicken as a whole.
6
6
Altocumulus
resulting from the spreading out of Cumulus (or Cumulonimbus).
7
5,
9, 103
Altocumulus
in two or more layers, usually opaque in places, and not progressively
invading the sky; or Altocumulus together with Altostratus or Nimbostratus.
8
4
Altocumulus
with sproutings in form of small towers or battlements, or Altocumulus
having the appearance of cumuliform tufts.
9
3
Altocumulus
of a chaotic sky, generally at several levels.
/
??
Altocumulus,
Altostratus and Nimbostratus invisible owing to darkness, fog, blowing
dust or sand or other similar phenomena, or more often because of the
presence of a continuous layer of lower clouds.
2 If no CM 1, 2, 4, 5, 6, 7, 8 or 9 is present, priority is determined by whatever type has the greatest sky cover.
3
This classification changes depending on what cloud type is most prevalent.
As and Ns have a higher priority than Ac at two or more levels, and Ac at
two or more levels has a higher priority than opaque Ac. (see flowchart for
clarification).
Scientific contact:
Professor Sandra Yuter, Project
Science Coordinator