Local weather & Aerology
Local aerology
The main aerological phenomena in the Arve Valley are the foehn and the Sallanches valley breeze.
Foehn
The Arve Valley and the surrounding valleys are regularly affected by foehn conditions.
This occurs when atmospheric pressure is higher on the Italian side of the Mont Blanc massif than on the French side. This pressure difference forces air to flow across the mountains and rise. On the leeward side, this results in rotors and very disturbed air.
Needless to say, flying in these conditions should be avoided, as turbulence can be severe.
To anticipate foehn conditions, you can check the atmospheric pressure difference between the Aosta Valley and Annecy. This can be done manually using forecasts from your favorite weather website, or by using the graph provided by Atmosoar. Foehn is generally considered likely when the pressure difference reaches −4 hPa or more. Positive values do not concern us, as in that case the Italian side is affected.
Other indicators include:
- High-resolution model forecasts at the exit of the Mer de Glace (watch for strong easterly gusts),
- Weather stations at Prarion, refuge du Requin, and ENSA in Chamonix (the latter is not always reliable in the presence of an inversion layer).
Valley breezes
The valley breeze enters from the Sallanches side, where it can be very strong, often making landing at the lake impossible during the day. It gradually weakens as it turns toward Passy. The breeze flow splits a first time around Mont d’Arbois and a second time at the entrance of the Saint-Gervais valley.
Sometimes, the return flow is very pronounced and comes back from the east / south-east on the Varan side.
Weather and aerological forecasts
Here are a few links to weather websites that are useful for paragliding flights in the Mont-Blanc area.
Weather analysis for beginners
Here are a few reminders of the key elements to take into account in your weather and aerological analysis.
You’ll find excellent resources to help structure your weather analysis on the Rocherbleu website, as well as a dedicated page: Flying in calm conditions.
Rocher bleu
Local weather forecast
In addition to the usual weather websites listed below, Chamonix Météo publishes daily forecasts. It is a reference source for local weather in the Chamonix valley. A daily bulletin is published every morning, with a 3-day forecast and a 5-day trend.
The Situation générale et évolution section at the beginning of the bulletin provides an overview of atmospheric pressure, synoptic wind and temperatures across the Alpine arc.
The day-by-day local forecasts detail cloud cover, precipitation, wind and temperatures at different altitudes.
These forecasts focus on the Chamonix Valley, the Mont-Blanc massif and the Aiguilles Rouges. However, extrapolating them to the Mont-Blanc plain (Passy / Sallanches), the Val Montjoie (Saint-Gervais / Les Contamines-Montjoie), the Aiguilles de Warens, Platé and the Fiz range is fairly straightforward and generally gives a reliable trend.
Classic weather forecast websites:
General situation: isobaric charts
Several resources provide isobaric charts that help you get a clear picture of the overall weather situation.
To learn how to interpret these charts, you can find tutorials here:
Weather wind stations
The weather stations at the Grandes Platières (accessible from spring to autumn) and at the Aiguille du Midi give a good indication of the synoptic wind at altitude, especially for north and south trends.
For west or east trends, you’ll need to look at the Prarion station, and possibly those at the Col de Balme and Tête de Balme.
All of these stations are available on Spotair.
Spotair
Emagrams
Several websites provide emagrams, which are very useful for planning a thermal flight!
You can find excellent resources to understand and interpret emagrams on the Rocherbleu website.
Precipitation and cloud radar
In addition to the usual radar tools you can find on meteoblue, MétéoFrance, météociel or windy, the Swiss website Search.ch, based on MeteoSwiss data, provides fairly reliable forecast radar for the valley.
View the weather radar on search.ch