Visibility, RVR and Obscuration Codes
Updated: 2026-09-27 · First published: 2026-09-27 · About this site
Visibility is the one weather element that can put an aerodrome below minima on a cloudless day. It is reported twice in a METAR — once as prevailing visibility for the aerodrome, and, when it is low enough to matter, again as runway visual range for a specific runway — and it is qualified by the weather group that explains why it is low. Fog, mist, haze, smoke, dust and sand all reduce visibility; they do it differently, last differently and clear differently.
Prevailing visibility
Outside the United States visibility is reported in metres: 4000 is 4 km; 0400 is 400 m; 9999 is 10 km or more. The steps are 50 m up to 800 m, 100 m up to 5 km, 1 km up to 10 km. In the US and its territories it is in statute miles: 1 1/2SM, 10SM, and in a TAF P6SM (more than 6 SM). "Prevailing" means the visibility reached or exceeded in at least half the horizon circle; when one sector is much worse, it is added with a direction — 4000 1200NE — so you know which approach is the bad one. //// means it could not be assessed.
Note what is not measured: slant visibility from the cockpit on final, which is often worse than surface visibility in shallow fog and better in haze. A runway that is visible from 3 km along the ground may disappear under a 200 ft layer on the approach; hence RVR.
Runway visual range
RVR is measured by transmissometers or forward-scatter sensors alongside the runway and represents the distance a pilot on the centreline can see the runway surface markings or lights. It is reported when the prevailing visibility or the RVR itself is below 1,500 m, one group per runway:
R24L/0650V1100D R24R/P1500 R06/M0050N
- R24L/0650V1100D — runway 24 Left, RVR varying between 650 and 1,100 m over the previous 10 minutes, tendency downward.
- R24R/P1500 — more than 1,500 m (above the reporting range).
- R06/M0050N — less than 50 m, no change. Nothing is landing on 06.
The tendency letter (U up, D down, N no change) is worth as much as the value: 650 m and rising is a different approach from 650 m and falling. Approach and take-off minima below about 1,500 m are always expressed in RVR, and where RVR is not available a conversion from visibility may be permitted by your operations manual — with a factor that depends on the lighting and the time of day.
The obscuration codes
| Code | What it is | Reported when | Behaviour |
|---|---|---|---|
| FG fog | Water droplets | Visibility < 1,000 m | Clears with heating or wind; see the fog guide |
| BR mist | Water droplets | 1,000 m ≤ vis < 5,000 m | Often the hour before or after fog |
| HZ haze | Dry particles (pollution, salt, smoke residue) | Vis < 5,000 m, humidity below saturation | Does not clear at sunrise; needs a change of air mass or wind |
| FU smoke | Combustion products | Any | Follows the wind from the fire; can be very local |
| DU dust / SA sand | Lifted mineral particles | Any; BLDU / BLSA when blowing | Wind-driven; DS/SS are dust storms and sandstorms with vis < 1,000 m |
| VA volcanic ash | Ash | Any | Engine hazard regardless of visibility |
| PO dust whirls, SQ squall, FC funnel cloud | Other phenomena | When observed | — |
Prefixes refine fog and precipitation: MI shallow (below 2 m — the runway markings vanish but the tower sees over it), BC patches, PR partial (covering part of the aerodrome), VC in the vicinity (5–8 km, not on the field), FZ freezing (fog depositing rime), BL blowing and DR drifting for snow, sand and dust.
Reading the combination
The visibility number and the weather code should agree, and when they do not, the disagreement is information. 2000 HZ at 32/12 is dry haze that the morning will not touch. 2000 BR at 14/13 is an hour from fog if the temperature keeps falling. 0300 FG VV001 is a closed airport. 9999 VCFG is a warning that the fog bank is over the fields next door and the wind may bring it in; check the neighbouring stations. Automated stations measure visibility at one point with a forward-scatter sensor, so a report of 9999 from an AUTO station at a fog-prone field, with a spread of 1 °C, should be read with the spread rather than the number. Every airport page on this site shows the visibility in your chosen unit, the RVR groups decoded per runway, and the obscuration type explained in plain language, so the combination is spelled out rather than left to the reader — try a foggy winter morning at EDDM Munich or LIMC Milan Malpensa.
Frequently asked questions
What does 9999 mean?
Prevailing visibility of 10 km or more. It is the top of the scale in metres, not a measurement of 9,999 m. US stations report in statute miles: 10SM is the equivalent, and P6SM in a TAF means more than 6 statute miles.
What is the difference between visibility and RVR?
Visibility is the distance a dark object can be seen against the sky, assessed by an observer or a forward-scatter sensor at one point. RVR (runway visual range) is measured by transmissometers beside a specific runway and describes how far a pilot on the centreline can see the runway lights or markings. RVR is used for approach and take-off minima below about 1,500 m.
What does R24L/P1500 mean?
RVR on runway 24 Left is more than 1,500 m — the P means the value exceeds the instrument's reporting range. M0050 would mean less than 50 m. A trailing U, D or N gives the tendency: up, down, no change.
When is BR reported rather than FG?
By visibility. Fog (FG) is water droplets reducing visibility to below 1,000 m; mist (BR) is the same droplets with visibility of 1,000 m to below 5,000 m. Haze (HZ) is dry particles, not water, and can be reported with any visibility below 5,000 m.
What does 4000 1200NE mean?
Prevailing visibility 4,000 m, but only 1,200 m in the north-east sector. The minimum directional visibility is added when it is less than 1,500 m or less than half the prevailing value. It tells you which approach direction is worse.
Read next
- How to Read METAR Reports: A Pilot's Guide — Learn to decode a METAR line by line: station, time, wind, visibility, weather, clouds, temperature, QNH and trend. Worked example plus the mistakes that catch pilots out.
- VFR vs IFR Flight Categories Explained — What the four flight categories mean, the exact ceiling and visibility thresholds, how to derive them from a METAR or TAF, and how they differ from flight rules and European colour states.
- How to Read a TAF Forecast — Decode a TAF: validity period, FM, BECMG, TEMPO and PROB groups, what each change group promises, and how to pick the worst period for alternate planning. Worked example included.
- Crosswind Component and Runway Selection — The sine rule, the clock-face shortcut, gust handling and a worked example. How crosswind, headwind and tailwind components decide which runway to use and when to divert.
- QNH, QFE and QNE: Altimeter Settings Explained — What each altimeter setting measures, when to use which, how to convert hPa and inHg, what a wrong setting does to your altitude, and how transition altitude and level work.
- All pilot guides — the full library, 15 articles.
- Airports by country — live METAR and TAF for every reporting station
- World weather rankings from the observation archive