High
clouds, CH
base usually 20,000 ft or above
over British Isles) |
| Type |
Precipitation
(ppn) etc. |
Range
of cloud base |
C
code |
| Cirrus
(Ci) |
No ppn. Halo may occur.
Dense patches may veil or hide the sun
|
Usually 20,000-40,000 ft
|
0
|
| Cirrocumulus
(Cc) |
No ppn. Position of sun/moon
can usually be seen
|
If at a non-aviation station
the height cannot reasonably be estimated,
the British practice is to use a nominal
height of 25,000 ft, and 35,000 ft
for any higher cloud
|
1
|
| Cirrostratus
(Cs) |
No ppn. Halo often occurs.
Outline of sun normally visible
|
Cs may thicken to become
As
|
2
|
|
Medium
clouds, CM
(base usually between 6,500 and 20,000 ft
over British Isles, although Ns may lower
to near earth's surface) |
| Type |
Precipitation
(ppn) etc. |
Range
of cloud base |
C
code |
| Altocumulus
(Ac) |
Ac Castellanus
occasionally produces ppn. Can be thick enough
to hide sun/moon |
Usually 6,500-20,000 ft.
If at a non-aviation station the height cannot
reasonably be estimated, the British practice
is to use a nominal height of 10,000 ft,
and 15,000 ft for any Ac or As above |
3 |
| Altostratus
(As) |
Often
continuous ppn reaching the ground with sun/moon
hidden. Thinner As shows sun/moon as ground
glass appearance |
Altostratus
may thicken with progressive lowering of the
base to become Ns |
4 |
| Nimbostratus
(Ns) |
Normally continuous
ppn (sometimes moderate/heavy) with sun/moon
hidden |
Usually between
the surface and 10,000 ft |
5 |
|
Low
clouds, CL
(base usually below 6,500 ft over British
Isles) |
| Type |
Precipitation
(ppn) etc. |
Range
of cloud base |
C
code |
| Stratocumulus
(Sc) |
Normally no
ppn, but slight ppn possible over coasts/hills.
Can be thick enough to hide sun/moon |
Usually between
1,000 ft* and 4,500 ft but may often
be observed to 6,500 ft |
6 |
| Stratus
(St) |
Near
coasts/hills, ppn can be considerable, but
it may be falling from higher cloud such as
Ns. Can be thick enough to hide sun/moon.
However when thin, sun/moon can be clearly
visible |
Usually
between the surface and 2,000 ft but
may sometimes be observed to 4,000 ft |
7 |
| Cumulus (Cu) |
Light showers
are possible |
Usually between
1,000 ft* and 5,000 ft, but may
sometimes be observed to 6,500 ft. After
initial formation, a rise in temperature often
leads to a rise in cloud base |
8 |
| Cumulonimbus
(Cb) |
Always
reported when showers/thunderstorms/hail occurs.
Squally winds are also common |
Usually
between 2,000 ft* and 5,000 ft,
but may sometimes lower to near surface, or
be as high as 6,500 ft |
9 |
| *At
stations substantially over 500 ft above
sea level the base will often be less. |
|
|
|
|
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