AIM
4/3/14
7−1−66
Meteorology
(a) Amount.
The amount of sky cover is
reported in eighths of sky cover, using the
contractions:
SKC
clear (no clouds)
. . . . . . . . .
FEW
>
0 to
2
/
8
. . . . . . . .
SCT
scattered (
3
/
8s
to
4
/
8s
of
. . . . . . . . .
clouds)
BKN
broken (
5
/
8s
to
7
/
8s
of clouds)
. . . . . . . . .
OVC
overcast (
8
/
8s
clouds)
. . . . . . . . .
CB
Cumulonimbus when present
. . . . . . . . . .
TCU
Towering cumulus when
. . . . . . . . .
present
NOTE
−
1. “SKC” will be reported at manual stations. “CLR” will
be used at automated stations when no clouds below
12,000 feet are reported.
2.
A ceiling layer is not designated in the METAR code.
For aviation purposes, the ceiling is the lowest broken or
overcast layer, or vertical visibility into an obscuration.
Also there is no provision for reporting thin layers in the
METAR code. When clouds are thin, that layer must be
reported as if it were opaque.
(b) Height.
Cloud bases are reported with
three digits in hundreds of feet above ground level
(AGL). (Clouds above 12,000 feet cannot be reported
by an automated station).
(c) (Type).
If Towering Cumulus Clouds
(TCU) or Cumulonimbus Clouds (CB) are present,
they are reported after the height which represents
their base.
EXAMPLE
−
(Reported as) SCT025TCU BKN080 BKN250 (spoken as)
“TWO THOUSAND FIVE HUNDRED SCATTERED
TOWERING CUMULUS, CEILING EIGHT THOUSAND
BROKEN, TWO FIVE THOUSAND BROKEN.”
(Reported as) SCT008 OVC012CB (spoken as) “EIGHT
HUNDRED SCATTERED CEILING ONE THOUSAND
TWO HUNDRED OVERCAST CUMULONIMBUS
CLOUDS.”
(d) Vertical Visibility (indefinite ceiling
height).
The height into an indefinite ceiling is
preceded by “VV” and followed by three digits
indicating the vertical visibility in hundreds of feet.
This layer indicates total obscuration.
EXAMPLE
−
1
/
8
SM FG VV006
− visibility one eighth, fog, indefinite
ceiling six hundred.
(e) Obscurations
are reported when the sky
is partially obscured by a ground−based phenomena
by indicating the amount of obscuration as FEW,
SCT, BKN followed by three zeros (000). In remarks,
the obscuring phenomenon precedes the amount of
obscuration and three zeros.
EXAMPLE
−
BKN000 (in body)
“sky partially obscured”
. . . . . . . .
FU BKN000 (in remarks)
“smoke obscuring five
−
. . .
to seven
−eighths of the
sky”
(f)
When sky conditions include a layer aloft,
other than clouds, such as smoke or haze the type of
phenomena, sky cover and height are shown in
remarks.
EXAMPLE
−
BKN020 (in body)
“ceiling two thousand
. . . . . . . .
broken”
RMK FU BKN020
“broken layer of smoke
. . . . . . . .
aloft, based at
two thousand”
(g) Variable ceiling.
When a ceiling is
below three thousand and is variable, the remark
“CIG” will be shown followed with the lowest and
highest ceiling heights separated by a “V.”
EXAMPLE
−
CIG 005V010
“ceiling variable
. . . . . . . . . . . .
between five hundred and
one thousand”
(h) Second site sensor.
When an automated
station uses meteorological discontinuity sensors,
remarks will be shown to identify site specific sky
conditions which differ and are lower than conditions
reported in the body.
EXAMPLE
−
CIG 020 RY11
“ceiling two thousand at
. . . . . . . . . . .
runway one one”
(i) Variable cloud layer.
When a layer is
varying in sky cover, remarks will show the
variability range. If there is more than one cloud
layer, the variable layer will be identified by
including the layer height.
EXAMPLE
−
SCT V BKN
“scattered layer variable to
. . . . . . . . . . . . .
broken”
BKN025 V OVC
“broken layer at
. . . . . . . . .
two thousand five hundred
variable to overcast”