3533. Small, visible mound-like protuberances on the bottom of cumulonimbus clouds, that are potential breeding grounds for waterspouts and tornadoes, are called __________.

Mamma clouds are mound-like protrusions on the underside of cumulonimbus clouds, often indicating potential for waterspouts and tornadoes. Ice prisms are ice crystals, rime is ice accretion on surfaces, and thunderheads refer to the entire cumulonimbus cloud, not the specific protrusions described.