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weather) will be inserted. A minus (-)
means light, no sign is moderate, and
+ means heavy. It is described in 7
ways, such as SH (showers), DR for
drifting, FZ (freezing), MI (shallow),
BL for blowing and BC for batches.
FC=Funnel Cloud (Tornado),
TS=Thunderstorm, DZ=Drizzle,
FG=Fog (< 1 km), BR=Mist (> 1
km), GS=Small Hail, FU=Smoke,
SS=Sandstorm, VA=Volcanic Ash,
PO=Dust/Sand, RA=Rain,
SG=Snow Grains, PL=Ice Pellets,
IC=Ice Crystals, SA=Sand,
SN=Snow, HZ=Haze, GR=Hail,
DU=Dust, SQ=Squall,
DS=Duststorm.
Cloud
Up to 4 cloud groups, in ascending
order of bases, and cumulative, based
on the amount of the sky covered, in
eighths, or oktas. The cloud ceiling is the
height of the first layer that is broken
or overcast. The first group is the
lowest individual layer; the second
the next of more than 2 oktas and
the third the next higher of more
than 4 oktas. A group has 3 letters
for the amount (FEW = 1 to 2
oktas, SCT, or scattered = 3 to 4
oktas; BKN, or broken, = 5 to 7
oktas, and OVC, or overcast = 8
oktas) and 3 for the height of the
cloud base in hundreds of feet above
ground level. For clear sky, expect
SKC. VV means vertical visibility in
hundreds of feet which, if you get it
at all, means an obscured ceiling. CB
means thunderstorms and is added
as necessary. Clouds may cover the
sky, but not conceal it if transparent,
hence the term opacity.
106 JAR Private Pilot Studies
Significant Changes
In addition to ‘FM’ and the time (see
above) significant changes may be
indicated by ‘BECMG’ (becoming)
or ‘TEMPO’ (temporarily).
‘BECMG’ is followed by a fourfigure
group indicating the beginning
and ending of the period when the
change is expected. The change is
expected to be permanent, and to
occur at an unspecified time within
it. ‘TEMPO’ will similarly be
followed by a 4-figure time group,
indicating temporary fluctuations.
‘TEMPO’ conditions are expected to
last less than 1 hour in each instance,
and in aggregate, less than half the
period indicated.
Probability
Probability of a significant change,
either 30 or 40%. The abbreviation
‘PROB’ will precede the percentage,
followed by a time group, or a
change and time group, e.g.:
PROB 30 0507 0800FG BKN004
or
PROB40 TEMPO 1416 TSRA
BKN010CB
Example
EGHH 0615 VRB06KT 9999
SCT 030
was issued at Heathrow for the
period 0600-1500, with variable wind
at 6 kts, visibility more than 10 km
and 3-4 oktas of cloud at 3000 above
the airfield elevation.
METARs
Meteorological Aerodrome Reports are
compiled half-hourly or hourly while
the met office is open, about 15
minutes after observations are made.
Missing information may be
indicated by oblique strokes.
They are reports, not forecasts, but you
may see an outlook tagged on the
end after the word TEND. It
represents a two-hour period from
the time of the observation. NOSIG
means no significant changes are
expected in the following two hours.
Message Type
METAR means a routine actual
weather report. SPECI means a
significant change off the hour.
Station Identifier
4-letter ICAO sign for aerodrome,
and observation time in UTC.
Winds
The first three numbers are the
direction to the nearest 10° and the
next two the speed in knots. G
means Gusts. 000000KT is calm,
VRB means variable, less than 3 kts.
Horizontal Visibility
The minimum is in metres, followed
by one of the eight points of the
compass if there is a difference in
visibility by direction, as with
4000NE. If the minimum visibility is
between 1500-5000 m in another
direction, minimum and maximum
values, and their directions will be
given, e.g. 1400SW 6000N. 9999
means 10 km or more, while 0000
means less than 50 metres.
Runway Visual Range (RVR)
An RVR group has the prefix R
followed by the runway designator,
then an oblique stroke followed by
the touch-down RVR in metres. If
RVR is assessed simultaneously on
two or more runways, it will be
Weather 107
repeated; parallel runways are
distinguished by L, C or R, for Left,
Central or Right parallel respectively,
e.g. R24L/1100 R24R/1150. When
the RVR is more than 1500m or the
maximum that can be assessed, the
group will be preceded by P,
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