What is the meaning of the NDV and NCD groups in METAR/SPECI?
These groups only appear in METAR AUTO, i.e. fully automated messages. The NDV group is appended to the visibility meter value to indicate that, as we have only one visibility meter per site, there is No Directional Variation reporting capabilty (as there is with manual reports). The NCD group reports that there has been Nil Cloud Detected by the cloud sensor.
