Taf...9000vdn

[cavortingcheetah]

:hmm:

If anyone down here has a clue what might be the significance of 9000VDN on a TAF at Annecy on 21.03, won't you please just pop up to Questions and out them out of their misery.
Mind you, having consulted Meteo France, Baroness Orczy and Marcel Proust, I would be interested in the answer as well.
:ooh:

[kwachon]

It's french for "vol de nuit", a french only abbreviation on TAF's therefore 9000vdn = vis 9000 at night. :ok:

[roljoe]

Hi,

it's not 9000VDN to be red but 9000NDV

The NDV stands for a situation where the visibility sensors are located in a way that no variation of direction could be indicated...

so to be red as No Direction Variation...which means that you could have a better value then indicated, just because the system does not enable a 360° look out..

ps..nothing to do with "vol de nuit" wich must remains "the book to read" from Saint-Exupéry...

[blue monday]

I asked the same Question at the weekend http://www.pprune.org/forums/showthread.php?t=319244

[PPRuNeUser0215]

ICAO Annex III

4.9.1.2 Recommendation.— In automated METAR and
SPECI, visibility should be reported in accordance with provisions
relevant to METAR and SPECI included in Section 4.2.
However, when visibility sensors are sited in such a manner
that no directional variations can be given, visibility value
reported should be followed by the abbreviation “NDV”.