# Visibility-Reducing Phenomena in Aviation

> Operational overview of visibility-reducing phenomena in aviation, including fog, haze, volcanic ash, dust, smoke, and precipitation effects.

- **Subject:** 050 — Meteorology
- **Section:** 050-09 — Flight Hazards
- **Topic code:** 050-09-09
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/meteorology/flight-hazards/visibility-reducing-phenomena/

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

![Volcanic Ash Cloud](https://upload.wikimedia.org/wikipedia/commons/0/09/Eyjafjallaj%C3%B6kull_volcanic_ash_15_April_2010.png)

## 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.

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.