However, there are exceptions:

* High clouds like cirrus can form as high as 13,000 meters (43,000 feet).

* Low clouds like stratus can form as low as 2,000 meters (6,500 feet), sometimes even touching the ground as fog.

* Cumulonimbus clouds, the thunderheads, can extend from low levels to as high as 18,000 meters (59,000 feet).

The specific altitude depends on factors like temperature, humidity, and air currents.