Mackerel Sky Sunset Photograph by John Leslie/Alamy A "mackerel
sky" adds to a striking sunset scene in Grimsby, Lincolnshire,
England. Ripples of altocumulus or cirrocumulus
clouds—resembling the markings of a king mackerel—give the
phenomenon its name. Altocumulus Undulatus Clouds Photograph by
Steven Haggard/Alamy Fluffy altocumulus undulatus clouds stain
the sky red above a row of trees. These mid-level clouds, which
form above 6,500 feet (2,000 meters), often herald an
approaching storm. Golden Gate Bridge in Clouds Photograph by
Tom Tracy Photography/Alamy San Francisco's Golden Gate Bridge
appears to float on a sea of surrounding clouds. Such low-level
clouds, called stratus clouds, occur below 6,500 feet (2,000
meters) and often bring rain or snow. Clouds that touch the
ground are known as fog. Photograph by Arco Images/Alamy The
summit of Washington's Mount Rainier lies hidden beneath a stack
of horizontally layered lenticular clouds. These clouds are
formed by high winds blowing over rough terrain a