Which side of a rocky knoll, surrounded by vegetation, should a pilot find the best thermals?

• A. On the side facing the sun
• B. On the shadowed side
• C. On the leeward side
• D. On the top of the knoll

Answer: (A)

Thermals form where the ground is heated by sunlight, creating rising warm air. A rocky knoll heats unevenly, and the sun heats the side facing it much more quickly than the shaded side. That sunlit surface drives stronger convection, so a vertical column of rising air develops there and is more usable for a glider. The shadowed side stays cooler and produces weaker updrafts. The top of the knoll can be turbulent due to wind over the ridge, making it less reliable for catching a smooth thermal. So the best place to find thermals is on the sunlit side of the knoll.