I understand that METARs from 25th Nov will have the visibility stated as
the 'prevailing' visibility - i.e the value that is at least the visibility
for half of the station horizon circle.
If there is reduced vis of less than 1500m or 50% of the value above that
will also be stated
i.e 7000 2000E
Could someone tell me what the current criteria is for quoting 2 visibility
values.
Thanks
Phil

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http://homepage.ntlworld.com/phil.layton/meteo.htm

Phil,
The change will only affect METARs from CIVIL airfields. The military are still
discussing the implications and may not make the change until sometime later.
Currently any double reporting of visibility again only occurs at Civil
airfields. military airfileds always report the worst visibility.
i believe civil METARs report two visibilities when they affect the runways