abstract:Cumulonimbus velum (Cb vel) (from the Latin cumulonimbus, "column-rain" + velum, "veil") is a cumulonimbus cloud with a small layer of altostratus cloud wrapped around its mid area, representing an area of humid stable air created as a result of the growth of the parent cumulonimbus. The altostratus velum cloud appears dark in comparison to its parent cloud, and can persist even after the cumulonimbus has disintegrated.