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The variation groups TEMPO and INTER areused to indicate significant
variations of a temporary or intermittent nature. The change groups FM and
BECMG are used to specify changes that aremore lasting in nature. The
indicators are the beginning of a self-contained forecast.
When reduced visibility due to fog,mist, dust, smokeor sand is forecast, but
the probability is assessed at between 30% and 40%, the terms PROB30 or
PROB40 are used. The termmay also be addedbefore a TEMPOor INTER
statement to express probability assessments of thunderstorms. If greater
than, or equal to, 50%probability is forecast, reference ismade to the
phenomena in the forecast itself and not by the addition of the statements
PROB30 or PROB40.
The termsNSW (nil significantweather), SKC andNSCmay be included
following FM or BECMG to indicate significant improvements expected.
If a TAF or TTF includes a forecast of turbulence, its commencementwill
be indicated by the abbreviation FM, and its cessationwithin the forecast
coveragewill be indicated by the abbreviation TILL. Start and finish times are
given in the format ddhhmm (day ofmonth, hour,minute).
Temperature
Aerodromeweather reports contain both air temperature anddewpoint in
whole degrees celsius.
Up to four forecast values of air temperature aregiven in TAF, for the times
HH, HH+3 hours, HH+6hours andHH+9 hours, whereHH is the time
of commencement of theTAF validity period. These forecasts arepoint
forecasts for these times but are valid for:
• in the case of the first value, ninetyminutes after the timepoint HH; and,
• for subsequent values, ninetyminutes each sideof the time point.
The temperature forecasts are prefixed by the letter T. Negative values are
indicatedby the letterM before the numeral.
QNH
QNH is given inwhole hectopascals using four figures.
In aerodromeweather reports, QNH is prefixedby the letter Q (e.g. Q0999).
Observed intermediate values are rounded down (e.g. 1001.9 is reported as
1001).
Up to four forecast values of QNH are given inTAF, for the timesHH,
HH+3 hours, HH+6hours and HH+9 hours, whereHH is the time of
2 – me t eorology
aerodrome forecasts and reports