Cumulonimbus has a deep vertical structure. Its upper part usually becomes smoother or fibrous and often spreads into an anvil or plume. In the sunset photograph, the broad upper spread is more revealing than its dramatic colour.
It makes the list because the top matters as much as the base when separating a towering cloud from ordinary cumulus. A nearby view may hide that top, so a single photo can leave the identification uncertain. This guide is for recognition; use official forecasts and warnings for decisions about thunderstorms.
Photo: Thennicke · CC BY-SA 4.0. Resized and recompressed; image retains its source license.
