They can exist as individual towers or form a line of towers called a squall line. Fueled by vigorous convective updrafts (sometimes in excess 50 knots), the tops of cumulonimbus clouds can easily reach 39,000 feet (12,000 meters) or higher.

Cirrus clouds are one of three different genera of high-étage (high-level) clouds. High-étage clouds form at 5,000 m (16,500 ft) and above in temperate regions. The other two genera, cirrocumulus and cirrostratus, are also high clouds.

troposphere
6.2 Ice Clouds. Ice clouds, also called cirrus clouds, are made up of ice crystals and start to form at altitudes of 5.5 km in temperate regions and of 6.5 km in tropical regions, making them the highest clouds in the troposphere. A small seed particle, or INP, is needed for heterogeneous ice nucleation.

Cirrus form very high in the atmosphere. Only at very high altitudes or latitudes do Cirrus produce rain at ground level. But if you notice that Cirrus begins to cover more of the sky, and gets lower and thicker, this is a good indication that a warm front is approaching.

Cirrus clouds
Cirrus clouds are the highest of all clouds and are composed entirely of ice crystals.

High clouds form in the highest and coldest region of the troposphere from about 5 to 12 km (16,500 to 40,000 ft) in temperate latitudes. At this altitude water almost always freezes so high clouds are generally composed of ice crystals or supercooled water droplets.

Lenticular clouds indicate great instability in that layer of the atmosphere, and form in areas of mountain waves. Like ocean waves, these waves of air bouncing over the mountains are anything but stable. It makes sense that it would be a “rough ride”.

Cirrus clouds are wispy, feathery, and composed entirely of ice crystals. They often are the first sign of an approaching warm front or upper-level jet streak. Unlike cirrus, cirrostratus clouds form more of a widespread, veil-like layer (similar to what stratus clouds do in low levels).

Cirrus clouds. All high clouds are a type of cirrus, a common cloud that can be seen at any time of the year. Height of base: 20,000 – 40,000 ft. Shape: Layered, tufty or patchy. Latin: cirrus – lock or tuft of hair. Precipitation: None. Cirrus clouds are short, detached, hair-like clouds found at high altitudes.

High-level clouds occur above about 20,000 feet and are given the prefix “cirro.” Due to cold tropospheric temperatures at these levels, the clouds primarily are composed of ice crystals, and often appear thin, streaky, and white (although a low sun angle, e.g., near sunset, can create an array of color on the clouds).

The three main types of high clouds are cirrus, cirrostratus, and cirrocumulus. Cirrus clouds are wispy, feathery, and composed entirely of ice crystals. They often are the first sign of an approaching warm front or upper-level jet streak.