More Than a Sunny Day
In the Alps, a clear blue sky can be deceptively inviting. While it's a basic requirement, it's not a guarantee of safe flying conditions. The real story of alpine weather is written by unseen forces: thermal updrafts, valley winds, and other micro-climates
that can change with startling speed. Unlike flying over flatlands, mountainous terrain creates its own weather, a dynamic system where temperature differences between sunny slopes and shaded valleys generate powerful air movements. Most paragliding accidents are not caused by equipment failure but by human factors, with misjudgment of weather being a leading cause. Therefore, understanding these invisible currents is the first and most critical step for any pilot, from the seasoned expert to the first-time tandem passenger.
The Unseen Forces of the Air
Several key weather phenomena define alpine flying. The most common is the 'valley wind'. As the sun heats the mountain slopes during the day, the warmer air rises. To replace it, cooler air is pulled up from the valley floor, creating an uphill wind that can be gentle and useful for gaining height but can also become strong and turbulent in narrow valleys by the afternoon. At night, the process reverses, with cool air sinking from the peaks into the valleys. Then there are thermals—columns of rising warm air that act like invisible elevators for paragliders. While essential for long flights, they can be powerful and, on days with strong temperature differences, can create turbulent conditions. The most notorious alpine wind is the 'Foehn'. This is a warm, dry wind that occurs when air is forced over the main alpine ridge, dropping its moisture and then descending rapidly on the other side. Foehn conditions create extreme turbulence and high wind speeds, making flying impossible and extremely dangerous. Experienced local pilots know to recognize the signs, such as a wall of clouds over the ridge or unusually clear, warm air, and will never fly.
Your Pre-Flight Checklist
Thoroughly checking the weather is non-negotiable. This means going beyond standard consumer weather apps, which often fail to capture the local, small-scale conditions of the Alps. Pilots in Switzerland rely on specialized resources. The official source, MeteoSwiss, provides detailed forecasts. Subscription-based apps like Burnair or the free AI-powered Wingcast offer highly specific analyses for hundreds of launch sites, detailing wind speeds, thermal strength, and Foehn risk. A pre-flight check should include looking at the general pressure systems, wind speeds at different altitudes (not just the surface), and any alerts for phenomena like Foehn. The pressure difference between the north and south sides of the Alps is a key indicator for Foehn; a significant gradient means staying on the ground. Many launch sites also have webcams and local wind stations that provide real-time data, which must be consulted right before takeoff.
Reading the Signs In-Flight
Weather observation doesn't stop once you're airborne. Pilots must constantly read the sky. Small, puffy cumulus clouds with flat bases often indicate good, usable thermals. Conversely, clouds that grow rapidly upwards into cauliflower shapes (cumulus congestus) are a sign of instability and a potential thunderstorm, a signal to land immediately. Lenticular clouds, which look like stationary lenses, indicate very strong winds at altitude, even if it feels calm lower down. A pilot's decision to fly, or to cut a flight short, is based on this continuous assessment. Commercial tandem pilots in Switzerland undergo rigorous training and licensing through the Swiss Hang Gliding & Paragliding Association (SHV-FSVL), which heavily emphasizes meteorology and risk management. Their decision to cancel or postpone a flight is always based on safety and must be respected.
