Je vous pose ca là les gars, c'est tiré de mes cours ATPL :
Visibility
Visibility in the METAR is represented by the next group, depicted in red in the example. In
the METAR, the reported visibility is the prevailing visibility and, may, under certain conditions,
include the minimum visibility. Here, the prevailing visibility is reported as 0800 metres.
Prevailing visibility is the visibility value which is either reached, or exceeded, around at least
half the horizon circle, or within at least half of the surface of the aerodrome. If the visibility
in one direction, which is not the prevailing visibility, is less than 1500 m, or less than 50% of
the prevailing visibility, the lowest visibility observed, and its general direction, should also be
reported.
Up to 10 km, the visibility is measured in metres. For example, 6000 means that the prevailing
visibility is 6000 metres. Once the visibility reaches 10 km or more, the code figure used is 9999.
Visibility of less than 50 metres is indicated by the code 0000. In this example the prevailing
visibility is 800 metres.
METAR EGTK 231020Z 26012G25KT 220V300 0800
In some instances, runway visibility information is given in a METAR; this is known as Runway
Visual Range (RVR.) RVR is given only when either the horizontal visibility or the RVR, itself,
is less than 1500 metres. The RVR group starts with the letter R, and then goes on to give the
runway in use, followed by the threshold visibility in metres.
In the following example, for Oxford Kidlington, we have a prevailing visibility of 800 metres,
with an RVR, at the threshold of Runway 30, of 1100 metres.
METAR EGTK 211020Z 26012G25KT 0800 R30/1100 If the RVR is more than the maximum reportable value of 1500 metres, the code P is used in
front of the visibility value, R30/P1500. If the visibility is less than 50 m then the prefix M will
be used e.g. R30/M0050
A letter can sometimes come after the RVR to indicate any trends that the RVR has shown. A U
means that the visibility has increased by 100 m or more in the last 10 minutes, e.g. R30/1100U.
A D shows that visibility has decreased by 100 m or more in that same time period, R30/1100D.
An N added to the visibility group shows that there is no distinct trend observed, R30/1100N.
Obscuration
If the sky at an aerodrome is obscured for reasons other than cloud cover, and cloud coverage
cannot easily be determined, the code VV is used in place of the cloud information. VV is
followed by the vertical visibility in hundreds of feet.
METAR EGTK 231020Z 26005KT 0300 FG VV002
(a) (
The highlighted codes in this METAR indicate that:
Visibility is 300 m in fog (a), the sky is obscured and the vertical visibility is 200 ft.
This METAR decodes as follows:
METAR for Oxford/Kidlington, observed at 1020 UTC on 23rd of the month; the surface wind
is 260° True, at 5 kt; the visibility is 300 m in fog (a); the sky is obscured with a vertical visibility
of 200 ft (
.
476
Meteorological Aerodrome Reports (METARs) 25
If the vertical visibility cannot be assessed, three forward slashes will replace the cloud height
figures, e.g. VV///.
The code CAVOK is frequently used in the METAR code, being the abbreviation for “cloud,
ceiling and visibility are OK.” If CAVOK is used, it will replace the visibility, RVR, weather and
cloud groups. There are four criteria which must be met in order for CAVOK to appear in the
METAR. These are:
• the visibility must be 10 kilometres or more.
• the height of the lowest cloud must be no less than 5000 ft, or the level of highest minimum
sector altitude, whichever is the greater.
• there must be no cumulonimbus or ‘towering cumulus’ (TCU) present.
• there must be no significant weather at or in the vicinity of the aerodrome.
METAR EGTK 231020Z 26012G25KT 220V300 CAVOK
Mais plutot que de faire mal aux mouches, j'espere passer une bonne soirée hein.
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VF-41 : "First To Fight, First To Strike"
