At approximately what altitude above the surface would the pilot expect the base of cumuliform clouds if the surface air temperature is 82 degrees Fahrenheit and the dewpoint is 38 degrees Fahrenheit?

• A. 10,000 feet AGL
• B. 6,000 feet AGL
• C. 8,000 feet AGL
• D. 12,000 feet AGL

Answer: (A)

The base of cumuliform clouds is governed by the lifted condensation level (LCL), which depends on how warm the surface air is and how moist it is. The larger the difference between surface temperature and dewpoint, the higher the cloud base will be.

With a surface temperature of 82°F and dewpoint of 38°F, convert to Celsius: 82°F ≈ 27.8°C and 38°F ≈ 3.3°C. The temperature-dewpoint spread is about 24.5°C. Use the approximate formula for the LCL height in meters: LCL ≈ 125 × (T - Td) = 125 × 24.5 ≈ 3060 meters. Converting to feet gives roughly 10,000 feet above the surface.

So the base of the cumulus clouds would be around 10,000 ft AGL. The lower or higher options don’t match this estimate given the 24.5°C temperature-dewpoint difference.