Foehn Advisor - Alps

Foehn is the wind that crosses the Alps driven by a pressure difference between the two sides of the range. Air rises on the high-pressure side (windward), descends warm and dry on the low-pressure side (lee) - and it is on the lee side that mountain wave, rotors and turbulence, at times severe, affect the Alpine valleys and the arrivals/departures of that side's airports.

South Foehn: higher pressure in Milan (LIMC) than on the north side - turbulence on the Geneva (LSGG), Zurich (LSZH) and northern-valley side. North Foehn: higher pressure on the north side - turbulence on the Milan/Lugano side and LIMC arrivals.

Manual criterion: a difference greater than 5-8 hPa between LSZH and LIMC is a strong indication of turbulence; flying 5,000-8,000 ft above the highest point of the range is recommended.