A "thunderhead" is a rounded mass of cumulus or cumulonimbus clouds which often appear before a thunderstorm.

Texas artist Florence McClung donated 37 works of art to the Dallas Museum of Art including this work by Charles T. Bowling.

National Weather Service, Albuquerque
Learn more about clouds in this 2013 video tutorial on cloud types.

US Army Meteorology Cloud Identification
Check out this 1966 army training video "Know Your Clouds" on YouTube.