Knuckles
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- Slang for lumpy protrusions on the edges, and sometimes the underside, of a thunderstorm anvil. They usually appear on the upwind side of a back-sheared anvil, and indicate rapid expansion of the anvil due to the presence of a very strong updraft. They are not mammatus clouds. See also cumuliform anvil and anvil rollover.
NOAA National Weather Service - Cite This Source - This Definition - Anvil, Anvil Dome, Anvil Rollover, Back-sheared Anvil, CB, CBMAM, Cumuliform Anvil, Mushroom, Orphan Anvil, SPRD