Which cloud-base feature is associated with a thermal's visual cue?

• A. A concave base
• B. A convex base
• C. A flat base
• D. An irregular base

Answer: (A)

A thermal shows lift in a localized core, and that vertical motion shapes the cloud base you see. When the strongest updraft is underneath the cloud, the condensation tends to begin in the center and the lower edge of the cloud base curves inward, giving a cup- or bowl-like appearance. This concave, or cupped, base is a clear visual cue that you’re in a rising-air column and can expect lift in that area, which is why this option is the best choice. A flat base would suggest a more diffuse lift, a convex base would imply a different airflow pattern, and an irregular base points to turbulence or wind shear rather than a clean core updraft.