A pyrocumulus cloud forms over the School Fire in the northern Blue Mountains, nearly 100 miles south of the Spokane area, where this picture was taken in August 2005. The heat from the fire was sufficient to lift the air to great heights which resulted in the formation of a pyrocumulus cloud. A pyrocumulus cloud forms if there is enough moisture and atmospheric instability over the intense heat source. Although not common, these clouds can grow large enough to produce lightning and possibly some light precipitation. Credit: NOAA