What is the required RVR observation when visibility is down to one quarter mile?

When visibility is down to one-quarter mile, the typical protocol does not require an RVR (Runway Visual Range) value to be coded in the observation. In conditions of significantly reduced visibility, such as one-quarter mile or less, weather observers typically note that the RVR may not be representative of the actual visibility conditions at the surface, particularly since such a low visibility reading often corresponds to the presence of heavy precipitation, fog, or other obscurations.

This is why the correct procedure is to note that RVR is not coded for this visibility range; it implies that either the RVR is not reliably available or is not necessary for reporting in the standard weather observation practices. Areas where RVR is typically noted usually have better visibility conditions, and guidance from meteorological standards indicates that RVR is less meaningful when visibility is extremely low. Therefore, in this specific case, no RVR is coded when visibility reaches one quarter mile.