The term ‘weather’ is used to describe visible phenomena apart from clouds. Weather includes smoke, fog, thunderstorms, rain, and drizzle but it does not include cumulus or cirrus. It is possible for weather to be experienced inside or outside of cloud.
RE (recent) is used to describe weather that has been observed since the last report but is no longer present.
VC (vicinity) is used to describe weather observed between 8km and 16km from the airport, but not at the airport.
Reports and forecasts that refer specifically to an aerodrome will only include cloud types when they are towering cumulus (TCU) or cumulonimbus (CB). All other cloud types will not be mentioned, only the amount of the sky covered by cloud.
However all cloud types may be included in other forecasts, such as area forecasts or the UK MetForm 214 (more on these later). Cloud types are referred to by their abbreviation. Thankfully, these are fairly simple once you get the hang of it:
Cumulus = Cu
Towering Cumulus = TCu
Cumulonimbus = CB
Stratocumulus = Sc
Altocumulus = As
Cirrocumulus = Cc
Convective clouds (cumuliform) are associated with showers of rain – abbreviated to SHRA or SH.
Stratus = St
Nimbostratus = Ns
Altostratus = As
Cirrostratus = Cs
Cirrus = Ci
Non-convective clouds (stratiform) are associated with continuous or intermittent rain or drizzle – abbreviated to RA or DZ.
Cloud cover is described by dividing the sky into eighths and stating how many eighths of the sky contain cloud. These eighths are called oktas. For example, if half the sky is covered we say there is 4 okats of cloud cover – because 4/8th’s of the sky is covered. These eighths are reported by the following abbreviations:
SKC/NCD = Sky Clear/No Cloud Detected
FEW = Few (1 to 2 oktas)
SCT = Scattered (3 to 4 oktas)
BKN = Broken (5 to 7 oktas)
OVC = Overcast (8 oktas)
LYR = Layers of clouds exist
The amount of cumulonimbus (CB) clouds is described as:
ISOL = Isolated
OCNL = Occasional, well separated
FRQ = Frequent, hardly or not at all separated
EMBD = Embedded in other clouds
In messages relating to an aerodrome, cloud heights are described by three numbers giving the cloud base above aerodrome level in hundreds of feet.
001 = 100ft above aerodrome level
010 = 1,000ft above aerodrome level
100 = 10,000ft above aerodrome level
In messages not relating to an aerodrome (e.g. area forecasts), cloud heights are given in altitude above mean sea level (AMSL).
These are then also described by how many oktas of the sky are covered, such as:
This would then decode to:
1-4/8 = 1 to 4 oktas of cover (FEW to SCT cloud)
CUSC = Cumulus and Stratocumulus
2500-3500FT/7000 = Cloud bases between 2,500ft – 3,500ft and cloud tops up to 7,000ft AMSL