When no motion of air is detected, the wind is reported as calm. A calm wind is coded as 00000KT.

Visibility is a measure of the opacity of the atmosphere. It is defined as the greatest horizontal distance at which selected objects can be seen and identified, or its equivalent derived from instrumental measurements.

Prevailing visibility is the reported visibility considered representative of recorded visibility conditions at the manual station during the time of observation. It is the greatest distance that can be seen throughout at least half of the horizon circle, not necessarily continuous.

Surface visibility is the prevailing visibility from the surface at manual stations or the visibility derived from sensors at automated stations.

The visibility group is coded as the surface visibility in statute miles. A space is coded between whole numbers and fractions of reportable visibility values. The visibility group ends with SM to indicate that the visibility is in statute miles. For example, a visibility of 1½ SM is coded 1 1/2SM. Most other countries use meters.

U.S. automated stations use an M to indicate “less than.” For example, M1/4SM means a visibility of less than ¼ SM.

The RVR is an instrument-derived value representing the horizontal distance a pilot may see down the runway.

RVR is reported whenever the station has RVR equipment and prevailing visibility is 1 SM or less, and/or the RVR for the designated instrument runway is 6,000 ft or less. Otherwise, the RVR group is omitted.

RVR is coded in the following format: The initial R is code for runway and is followed by the runway number. When more than one runway is defined with the same runway number, a directional letter is coded on the end of the runway number. Next is a solidus (/) followed by the visual range in feet, and then FT completes the RVR report. For example, an RVR value for Runway 01L of 800 ft would be coded R01L/0800FT. Most other countries use meters.

In the United States, RVR values are coded in increments of 100 ft up to 1,000 ft, increments of 200 ft from 1,000–3,000 ft, and increments of 500 ft from 3,000–6,000 ft. Manual RVR is not reported below 600 ft.

For U.S. airports only, the touchdown zone’s (TDZ) RVR is reported. For U.S. airports with multiple runways, the operating runway with the lowest touchdown RVR is reported. RVR may be reported for up to four designated runways in other countries.

When the RVR varies by more than one reportable value, the lowest and highest values will be shown with V between them, indicating variable conditions. For example, the 10-minute RVR for Runway 01L varying between 600 and 1,000 ft would be coded R01L/0600V1000FT.

If RVR is less than its lowest reportable value, the visual range group is preceded by M. For example, an RVR for Runway 01L of less than 600 ft is coded R01L/M0600FT.

If RVR is greater than its highest reportable value, the visual range group is preceded by a P. For example, an RVR for Runway 27 of greater than 6,000 ft will be coded R27/P6000FT.