What you're really asking is how high thunderstorm bases are above the ground, since “lightning clouds” refers to a cumulonimbus cloud. read more
Clouds found 100 feet off the ground are not “lightning clouds”; they may be accessory clouds to the thunderstorm such as scud or wall clouds, but lightning forms much higher up in the storm, usually between 15,000 and 25,000 feet, and then works its way down to the surface. read more
The ground in turn warms the air directly over the ground. Air, when warmed becomes less dense and lighter than the air around it. The air around it pushes in from the sides and the warm air rises. read more
Clouds are classified into four basic categories, depending largely on the height of their bases above the ground. High-level clouds, called cirrus clouds, can reach heights of 20,000 feet (6,000 meters) and are typically thin. read more