On which side of a sunlit rocky knoll should a pilot find the best thermals?

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

Answer: (C)

Thermals form when the sun heats the ground, warming the air above it and making that air buoyant enough to rise. On a sunlit rocky knoll, the side that faces the sun absorbs more heat, so the air there becomes lighter and rises more strongly, creating the best lift for a glider. The shaded or shadowed side stays cooler and produces weaker or no thermals because there isn’t as much heat to drive buoyant updrafts. The top of the knoll can be windy and may generate other forms of lift, like ridge or rotor effects, but they aren’t the steady, buoyant thermals pilots look for. So the optimal place to find the strongest thermals is the side facing the sun.