Over the last weekend, the foehn prevented all air traffic in the Valley. This impacts heavily on the PGHM and their resources.
Saturday, 01 Feb 2014, the PGHM rescue team had to make all the emergency rescue operations on foot, due to the unusual strong effect of the foehn that prevented PGHM's helicopters from taking off.
The first call of the was to assist a skier with a dislocated shoulder at the domaine du Balme, above Le Tour. The next call came from le Brevent where another team went into the assistance of a women with a sprained ankle. Later in the afternoon, a team responded to a call for assistance at Pré du Rocher (below Plan de l'Aiguille) where two people had become disorientated. Another incident took place on the Pas de Chèvre, an off-piste route situated between Aiguille des Grands-Montets and Vallee Blanche. A groupe of five skiers became strainded in a crevasse field and required assistance to make a safe exit to the Mer de Glace.
The Foehn continued into Sunday, 02 Feb 2014, and the PGHM was called upon once again. This time was just a short drive from their base in Chamonix. At 3.30pm, a young Norwegian paraglider pilot missed the winter landing field and became entangled in a tree at Moussoux. The ash tree had already been damaged in a recent storm so that it was not possible for a rescuer to climb the same tree. Sebastien Lucena climbed an adjacent tree, secured a rope to the tree an threw the other end to the stranded pilot, he clipped in, took the slack out of the rope and then the pilot unclipped from her paraglider. Sebastien controlled her swing so that no injury was inflicted on the flyer and she was lowered to the ground after her frightening experience.
Flying a paraglider during the foehn is never recommended.
The Foehn Effect is notorious amongst pilots and mountaineers, not only in the Alps, but in other mountain ranges across the world for its elevated temaperatures tat cause a repid thaw, the turbulent wind that makes flying dangerous or impossible and the constant small pressure changes, which if sustained over several days, can cause headches, nausea and poor coordination in some people.
A Foehn is a dry, warm, down-slope wind that occurs in the lee (downwind side) of a mountain range when the air is forced to flow against and over a mountain range in a short period of time. The air cools as it rises up the mountain, but at a reduced rate because water vapor with latent heat condensates allowing precipitation. Close to the summit, the air is dry and relatively warm for the altitude and it's been driven over the mountain by the ongoing effect. As the air descends, it falls into a chaotic flow which pilots call rotar. Flying in severe rotar is impossible, because lift cannot be sustained.
This is why the PGHM could nort use helicopters over the weekend and why the paraglider pilot, who landed in the tree, should not have taken off.
