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respectively. When an individual layer (mass) or cloud is composed of cumulonimbus
and towering cumulus with a common cloud base, the type of cloud is reported as
cumulonimbus only.
Cloud details will be written as one word for each layer being reported; eg 8/8ths of
stratus at 500FT will be given as “OVC005” and not “OVC 005”
Whenever cumulonimbus cloud is forecast, the degree of associated thunderstorm
activity or probability of occurrence is included.
Cloud information is not included if there is no cloud. When the sky is obscured,
the group is omitted in a report and included in a forecast only if cloud is forecast.
Vertical visibility is never included.
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AVIATION FORECASTS
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SIGNIFICANT VARIATIONS
Aerodrome forecasts may include an indicator of significant variation if changes in one,
or more of the elements of wind, visibility, weather or cloud, which would satisfy the
amendments criteria, are expected. These relate to improvements as well as
deteriorations.
The terms TEMPO and INTER are used to indicate significant variations of a temporary
or intermittent nature. The term FM Is used to indicate changes which are more lasting
in nature. The indicator is the beginning of a self-contained forecast or trend.
When reduced visibility due to fog, mist or dust is forecast, but the probability is
assessed at between 30% and 40%, the term PROB (percent) is used. The term may
also be attached to TEMPO and INTER conditions.
The terms WX NIL,NO SIG WX and SKC may be included following a significant
variation indicator, to indicate significant improvements expected.
If a TAF or TTF includes a forecast or turbulence, its commencement will be indicated
by the word “FM”, and its cessation within the forecast coverage will be indicated by
the word “TILL”
TEMPERATURE
Aerodrome weather reports contain both temperature and dewpoint.
Forecasts of air temperature are given at three-hourly intervals for a maximum of nine
hours, from the time of commencement of validity of the forecast. The temperature
groups are prefixed by the letter “T”.
QNH
QNH is given as a whole number of hectopascals, with observed intermediate values
being rounded-off downward. QNH is always given using four figures, prefixed by the
letter “Q”, eg: Q0997
SUPPLEMENTARY INFORMATION
In METAR/SPECI, supplementary information is used to provide reported wind shear
information on a take-off or landing runway. Additionally, weather observed since the
time of the last report, but not at the time of the observation, is reported using one or
more of the groups on page 134.
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AVIATION FORECASTS
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TREND TYPE FORECAST (TTF)
TTFs are prepared for the following locations:
Adelaide, Amberley, Brisbane, Darwin, Cairns, Canberra, East Sale, Launceston,
Melbourne, Nowra, Oakey, Pearce, Perth, Rockhampton, Sydney, Townsville and
Williamtown.
Note: The provision of TTF at some aerodromes is limited to routine flights only.
METAR/SPECI is normally available outside these hours.
TTF is defined as an aerodrome weather report (METAR/SPECI) to which a statement
of trend is appended. The TTF relates to weather conditions expected to affect the
aerodrome of origin for three hours following the time of the report.
The TTF supersedes the TAF for its validity period of three hours commencing at the
time of the observation and is the current forecast for pilots of aircraft whose arrival
time falls within the three-hour period. For aerodromes where the TTF service is not 24
hour service, or the meteorological watch ceases, the TAF will supersede the remaining
portion of the TTF validity for which a meteorological watch is not available. The time
at which the TAF supersedes the TTF will be included in the remarks section of the TTF.
Note: For pilots whose arrival time falls outside the three-hour period, the TAF is the
current forecast.
Where applicable, TTF replaces TAF and present weather in VOLMET broadcasts.
AUTOMATIC WEATHER STATIONS WITH CEILING AND VISIBILITY
INFORMATION
Automated cloud and visibility elements of an AWS will not be included in the body
of METAR and SPECI, but will be included in the remarks section of the report.
Cloud will be reported as SCT, BKN or OVC for amount, whilst visibility is a measure
of the average visibility for a small area. Pilots should regard automated cloud and
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