Wall cloud - Towering cumulus with rain-free base.
A wall cloud, a lowering of the cloud base underneath main storm
updraft, forms in this thunderstorm. Tornadoes can form out ot the wall clouds.
Image ID: nssl0044, NOAA's National Severe Storms Laboratory (NSSL) Collection Photo Date: 1982 Credit: NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL)