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132

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