# Local winds and associated weather

> Detailed analysis of local winds like Foehn, Mistral, Bora, and Sirocco for aviation meteorology.

- **Subject:** 050 — Meteorology
- **Section:** 050-08 — Climatology
- **Topic code:** 050-08-04
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/meteorology/climatology/local-winds-and-associated-weather/

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There are specific winds in various regions of the world that have significant characteristics and effects on aviation.

## Harmattan

*   **Origin**: It is a **Northeast (NE)** trade wind blowing from the high-pressure desert areas of North Africa (Sahara).
*   **Region**: West Africa (towards the Gulf of Guinea and the ITCZ).
*   **Season**: Winter (**November to April**).
*   **Characteristics**:
    *   **Cool, dry, and dust-laden** wind.
    *   **Visibility**: Can be drastically reduced (below 1000 m).
    *   The dust layer can extend up to **7,000 - 10,000 ft**.

## Foehn Effect

![Foehn wind illustration](https://upload.wikimedia.org/wikipedia/commons/0/0d/Foehn_wind_illustration.svg)
*Diagram showing windward uplift and leeward dynamic warming characteristic of the Foehn wind.*

The Foehn is a **warm, dry, and gusty** wind that descends the leeward slope of a mountain range.

### Formation Mechanism
1.  **Windward**: Air is forced to rise. It cools adiabatically (first DALR, then SALR after saturation). Moisture condenses forming clouds and precipitation, releasing latent heat.
2.  **Summit**: The air has lost much of its moisture.
3.  **Leeward**: The air descends and compresses, warming at the **DALR** (Dry Adiabatic Lapse Rate) throughout the descent.

### Result
The air reaches the leeward valley much **warmer and drier** than when it started rising on the windward side.
*   **Windward Side**: Low clouds, precipitation, poor visibility, risk of icing.
*   **Leeward Side**: Clear skies, good visibility, **turbulence**, high temperatures.

## Mistral

*   **Type**: Valley (channeled) and katabatic wind.
*   **Location**: Rhone Valley (Southern France) towards the Gulf of Lion (Mediterranean).
*   **Direction**: North / Northwest (**N/NW**).
*   **Cause**: High pressure in the Bay of Biscay and Low pressure in the Gulf of Genoa.
*   **Characteristics**:
    *   **Strong, cold, and dry** wind.
    *   Frequent in winter and spring.
    *   Usually brings clear skies but with severe turbulence.

## Bora

*   **Type**: Katabatic wind.
*   **Location**: Adriatic Sea coast (Croatia, Italy).
*   **Direction**: Northeast (**NE**).
*   **Cause**: Cold air accumulated over the Balkans/Central Europe (High pressure) falling towards the Adriatic (Low pressure).
*   **Characteristics**:
    *   **Very cold and dry** wind.
    *   Extremely gusty (gusts > 100 kt).
    *   Stronger in winter.

## Other Winds

*   **Sirocco**: South/Southeast wind in the Mediterranean, coming from the Sahara. Warm and dusty at source, becomes moist when crossing the sea.
*   **Pampero**: Outbreak of cold polar air in South America (Argentina/Uruguay).

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