Warm season scattered thunder-storms are omnipresent in northern California. They can be quite severe and often come without precipitation reaching the ground. Lightning strike under such conditions is extremely hazardous often initializing forest fires. Such a rapidly growing thunderstorm cloud, called cumulo-nimbus is photographed at its light to shadow boundary.
Pentax K2, Sigma 70-300mm, f/5.6, 1/1000sec, Kodak Ektachrome E6, ISO 100, polarization filter