The pilot hiked to the top of the North Side and noticed the wind at the top had switched from 4mph out of the northwest to 3mph out of the Southwest. After kiting along the road at the top the pilot launched downwind. Soon after launching the pilot encountered leeside thermic lift. Not expecting lift the pilot turned west. The lower wind sock was showing light northeast wind. Despite the lower wind sock direction the pilot noticed his approach landing speed was above 30mph. Suddenly the pilot's glide angle dropped more quickly the last 20 feet and unable to complete a flare he hit the ground hard.
Switching base wind with leeside thermals pulling localized wind toward the thermal core made a complex mix of convoluted air for the pilot to fly through. From his description it is likely that he was flying in zero to light downwind air into stronger down wind air with the transition causing the sudden drop similar to flying through a wind gradient.
Strong thermals will always mess up what we believe the local wind direction to be. Nonetheless, the safest conditions are with base winds consistent in both strength and direction or no wind at all. The highest risks come with high winds followed closely by switching winds.
From the book of risk:
Turbulence can be knowable with some education in weather and wind effects. Study the weather a lot, read a lot of books about weather especially that related to paragliding and hang gliding:
Understanding the Sky by Dennis Pagen
Thermal Flying by Burkhard Martens
Mastering Thermaling by Kelly Farina
Weather for Dummies
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