Local winds and associated weather

050-08-04Pablo Asensio Martínez2026-04-012 min

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 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).