When we find Yan Giezendanner in Chamonix, at his home at the foot of Mont Blanc, he is in transit between the Himalayas, Aconcagua and Fitz Roy. As a weather router, he devotes his life to moving from one continent to another, from one high peak in the world to another, throughout the seasons. Without leaving his office at Les Pèlerins. Yan’s history with weather forecasting and mountains is not new. In the 1950s, his father briefly moved to Chamonix to climb and ski. Should we see a sign there? In any case, the young boy, born in Paris and who lived in Switzerland, has always been interested in nature and changing skies. His walks and hikes allow him to be as close as possible to this constantly renewed palette of sensations.
In the mid-1970s, at a time when the weather had perhaps not yet become the contemporary obsession we know, the young man joined the National School of Meteorology in Saint-Cyr (established since 2021 in Toulouse). Upon leaving his training in 1977, he obtained, somewhat by chance, a position as a forecaster at Météo-France Chamonix. A happy coincidence because the Chamonix valley and the surrounding reliefs will quickly occupy a special place in his love of nature. This attraction led him to travel the mountains, in the summer on foot, in the winter on skis. Running to high mountain peaks? It’s not really his cup of tea. The forest and mountain pastures are preferred. “I am a contemplative. Nothing like seeing the clouds running over the summit of Mont Blanc”. Having a little perspective to see the big picture is better.
The most listened to answering machine in France
The weather forecast offices are located at the Maison de la Montagne, above the offices of the Compagnie des Guides and a few dozen meters from the Haute Montagne Gendarmerie Platoon. The young forecaster is directly in contact with those who make the heart of the world capital of mountaineering and skiing beat, from Frison-Roche to the stars of the moment, Boivin, Profit, Escoffier, including the anonymous people who ski and climb. For everyone, the weather report from the center of Chamonix for Haute-Savoie is an unmissable event, three times a day. The center was created on the initiative of Maurice Herzog, following several tragedies in the Mont-Blanc massif (notably the Vincendon and Henry affair). At the foot of the highest peak in Europe, it is an emblematic place for mountain weather. “At certain times, the answering machine was one of the most consulted in France”remembers Yan. In the evening, we gather in front of the window of the pharmacy on rue Vallot to see the bulletin typed on carbon paper. “I felt a certain pressure not to make a mistake, a pressure linked to frequenting the mountains and tourist activity. The issue of credibility is high. And at the beginning, the digital models available did not exceed 48 hours…”.
“I am a contemplative. Nothing like seeing the clouds running over the summit of Mont Blanc”
Yan’s experience draws on numerous feedback from those who are in the field and experience the realization of the forecast up close. He also trained with the site manager Jean-Jacques Thillet, one of the pioneers of mountain weather, who brought him knowledge of the massif and the demand for precision, rigor and conciseness that the profession requires. “Weather situations were perhaps simpler to analyze than today. The winter was long, more marked, with very heavy snowfalls even in the valleys, followed by marked anticyclones and temperatures down to -15°C, -20°C regularly. Today with global warming, it is very different. Rainy autumns and springs, snow accumulations at high altitudes in spring, a summer that comes very quickly, rapid changes. Besides, I’m not sure that the people who have settled in the valley in recent years would tolerate the rigor of the winters before. I also remember the big avalanches in the winters of the 80s…”.
Shipments in demand
From the mid-1990s, Yan’s gaze, through his screens, was drawn towards the distant massifs. The increase in the number of shipments and the multiplication of commercial shipments are already being observed, together with a technological revolution called the Internet. Weather maps begin to circulate and are quickly sent to miniaturized phones that teams carry on expeditions. They are fond of forecasts on the evolution of conditions in order to determine the right slots, in particular that of the famous summit push.
“Little by little, I will be seconded for one month a year, then several months, to be the contact person for these expeditions who subscribe to this weather routing service. It is preparation work, upstream, which intensifies over the course of the experience. The typical schedule is one bulletin per day during the acclimatization phase. Then it accelerates until it becomes almost permanent. It’s all the easier since today, information is exchanged by SMS.” Little by little, Yan accumulates experience. It is made up of hours spent in front of his computers and his weather maps, in front of Google Earth and especially with his clients on the highest peaks in the world, despite the handicap which immobilizes him in his wheelchair.
From K2 to El Niña
Now retired from Météo-France, the weather router continues his independent activity in his Pèlerins office. Around twenty expeditions around the world keep him busy for around eight months a year, from the Himalayas to Patagonia via Denali, in Alaska. This year he was at K2 with Liv Sansoz, Zeb Roche and Benjamin Védrines who paraglided from the summit on July 28. “Each area has its own specificities. For example, Patagonia is complicated, the periods of bad weather are long and the windows are very short, you have to seize them”. Obviously, mountaineers know that in these high altitude territories, even more than elsewhere, forecasts are…just forecasts. The relevance of a forecast and its ability to be used well also depends on non-weather factors, notably the context in which the group operates on the ground and its constraints. “I manage to have a certain finesse, I surprise myself”says Yan, smiling. The forecaster has one certainty: with his experience, he knows in which contexts he can be wrong. A habit of probabilities linked to field experience. And tomorrow with AI, things will become even more refined.
“The relevance of a forecast and its ability to be used well also depends on non-weather factors, notably the context in which the group operates on the ground, its constraints”
Our interview is coming to an end. Yan looks up from his computer. On the Goûter needle, a cloud unravels in this gentle autumn. Addicted to the weather, one question burns on our lips: “And for this winter in the Alps, what do you see? ». The models tell him about El Niña. He would not necessarily be surprised by a snowy winter in our Alps. We would like to be.
