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Note: Pilots should exercise cautionwhen interpreting automated visibility,
presentweather and cloud information as data from these instruments
may not be equivalent tohumanobservations.
Wind
Wind direction is rounded to the nearest 10 degrees and is given in three
figures relating toTrueNorth.Wind speeds aregiven in two figures.When
thewind is calm, thegroup is encoded as 00000KT.
A variablewind direction is given as VRB and is usedwhen the reporting or
forecastingof ameanwind direction is not possible, such as in the following
conditions:
• Lightwinds (3 kt or less).
• When forecasting a single direction is not possible; e.g. with a tropical
cyclone, orwith thepassage of a thunderstorm, inwhich case the
forecastwindmight be, for example,VRB60KT.
Maximumwind speed is givenonlywhen it is 10 kt ormoregreater than the
meanwind speed. It is indicated by the letter Gwhich is followed by the
maximumwind speed; e.g. 280°,mean speed 20 kt,maximum speed 35 kt,
is given as 28020G35KT.
Visibility
In TAF, theprevailing visibility (thegreatest visibility coveringmore than half
the aerodrome) is always given.
InMETAR/SPECI, if the visibility is not the same indifferent directions and:
• theminimum visibility is the prevailing visibility, or
• the visibility is fluctuating rapidly, then
theminimum visibility is the only informationprovided. Otherwise, both
the prevailing visibility and theminimum visibilitywill begivenwhen the
minimum visibility is less than 5000m. In this case theprevailing visibility
is reported first followed by theminimum visibility including an indicator
to show the general direction of theminimum visibility in relation to the
observing point (themeteorological station), e.g. the visibility groups 9000
0600N indicate a prevailing visibility of 9000m and aminimum visibility of 600
m to the north.
A visibility of 10 km ormore is given by 9999.
AutomaticVisibility Information
A report from anAWSwith a visibility sensorwill include data from this
aerodrome forecasts and reports
2 – me t eorology