Any one got an explanation or view on this?
I'll try.............
Met Vis is the LOWEST vis observered in all directions. RVR is the vis observed only in the direction of the runway (at the average pilot's eye ht.....blah)
Some examples:
(1)I am on the threshold of R/W 27 looking west. Down the R/W I can see for 2000m, to the north I can see for 4000m , to the south I can see for 4000m and to the east I can see for 4000m. Now, here the met vis would be 2000m as would the RVR be.
(2) I am, again, stood on the threshold of R/W 27 looking west. Down the R/W I can see for 4000m, to the north I can see for 2000m, to the south I can see for 2000m and to the east I can see for 2000m. In this case the met vis would be 2000m; however, the RVR would be 4000m.
Hopefully you can see from these examples that if the direction of worst vis is in the same direction as the R/W RVR will equal met vis; however, the RVR can never be less than the met vis.
No doubt somebody will get all technical about the exact definitions of met vis and RVR, but hopefully that helps?