RVR

Runway Visual Range is measured along a named runway, usually by instruments beside it, and is reported separately from the general visibility. It matters because the general figure describes the aerodrome as a whole while an approach depends on what can be seen down the strip of tarmac actually being used.

The group starts with R, then the runway designator, then a slash and the range in metres: R25L/0600 is 600 m on runway 25 left. Two prefixes bound the instrument range — M means less than, so R16/M0050 is below 50 m, and P means more than, so R07/P2000 is above 2 000 m. A trailing U, D or N reports the tendency: improving, worsening, or no change.

RVR is only included when it matters: it is reported when visibility or the RVR itself falls below 1 500 m. Its presence in a METAR is therefore itself a signal, and its absence in otherwise poor weather usually means conditions have not yet reached that threshold. Several runways may be reported in one observation, each as its own group.