Visibility-Reducing Phenomena in Aviation

050-09-09Pablo Asensio Martínez2026-04-012 min

Aeronautical visibility can be reduced by various meteorological phenomena, which are classified into hydrometeors (water) and lithometeors (solid particles).

Volcanic Ash Cloud

Obscurations

  • Fog (FG): Suspended water droplets. Horizontal visibility less than 1000 meters.
  • Mist (BR): Suspended water droplets. Horizontal visibility from 1000 to 5000 meters.
  • Haze (HZ): Suspended dry particles (dust, salt, smoke). Scatters sunlight, giving the sky an opalescent hue.
  • Smoke (FU).
  • Volcanic Ash (VA).
  • Widespread Dust (DU).
  • Sand (SA).

Precipitation

Precipitation reduces visibility depending on its intensity and type:

  • Drizzle (DZ): Typical visibility between 500 m and 3000 m.
  • Rain (RA):
    • Moderate: 3000 m to 5500 m.
    • Heavy: Can drop below 1000 m.
  • Snow (SN): Reduces visibility much more than rain.
    • Moderate: ~1000 m.
    • Heavy: 50 m to 200 m.

Wind-blown Snow

  • Drifting Snow (DRSN): Snow raised by the wind to a height of less than 2 meters (6 feet). Mainly affects taxiing, but usually does not obstruct vision at the pilot's eye level in flight.
  • Blowing Snow (BLSN): Snow raised to a height of 2 meters (6 feet) or more. Severely reduces horizontal visibility (can reach less than 1 meter) and is a major hazard to flight.

Sand and Dust Storms

  • Moderate: Visibility between 200 m and 600 m.
  • Heavy: Visibility less than 200 m.

Effect of Sun and Haze (Sun Glare)

Flight visibility (especially slant range visibility) degrades significantly when looking into the sun in hazy or misty conditions, due to light scattering by suspended particles.

  • Landing/Takeoff towards the West (Runway 27) at sunset: Worst visibility.
  • Landing/Takeoff towards the East (Runway 09) at sunrise: Worst visibility.

Shallow Fog (MIFG)

It is a thin layer of fog near the ground (usually radiation fog).

  • Hazard: From above (on approach), the pilot can clearly see runway lights and markings through the thin layer. However, when descending for landing (during the flare), horizontal visibility is suddenly lost upon entering the fog layer.