FULLY DEVELOPED CUMULONIMBUS CLOUD SHOWING INTERNAL CURRENTS. AFTER THIS STAGE THE CLOUD WILL DECLINE.

N. H. Birch and A. E. Bramson, Pilot's Guide to Flight Emergency Procedures. Doubleday, 1978.

Rain. The problems of flying in the heavy rain associated with cumulus and cumulonimbus clouds are primarily those of reduced visibility, the risk of airframe and engine icing (dealt with in Chapter 10) and, in extreme cases, the lowering of the cylinder-head temperature.