Under what conditions is RVR reported in a METAR?

RVR, or Runway Visual Range, is reported in a METAR primarily when visibility is 1 statute mile or less. This is crucial for pilots and air traffic controllers as it provides information about the actual visual range available to pilots for takeoff and landing operations, especially during periods of low visibility. When visibility drops to this level, the reported RVR is generally considered more accurate than the horizontal visibility, as it directly informs flight operations related to specific runways.

The other conditions presented do not warrant RVR reporting for a METAR. For instance, visibility at 2 statute miles or greater is usually sufficient for regular visibility reporting and does not necessitate the more specific RVR data. Factors like icy runway conditions and cloud cover also don't dictate the need for RVR reporting; instead, they may affect operational considerations but do not change the visibility measurement requirements for METARs. Thus, B is the correct context for understanding when RVR is included in meteorological reports to ensure safe aviation operations.