weather theoryFAA-published question bank (Private Pilot, 2008)
What is the approximate base of the cumulus clouds if the surface air temperature at 1,000 feet MSL is 70 °F and the dewpoint is 48 °F?
A
4,000 feet MSL.
B
5,000 feet MSL.
C
6,000 feet MSL.✓ Correct Answer
Explanation
Unsaturated rising air and its dewpoint converge at about 4.4 degrees F per 1,000 feet. The spread is 70 - 48 = 22 degrees F, and 22 / 4.4 = 5, so the base is about 5,000 feet above the surface; with the surface at 1,000 feet MSL, the cumulus bases are near 6,000 feet MSL.
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