They are very weak in terms of rain, because of their fog-like nature, but they can sometimes cause moisture and brief condensation to fall. They form when vertical air currents lift a thin layer of air to a point where condensation is possible. Cirrus clouds are the thin clouds that usually stretch from west to east across a sky. They resemble a beard, and many ancients thought they were the hair of deities in the sky. These clouds always form above 18,000 feet, and are non-rain in nature.
Cumulus clouds form when strong air currents point upwards.
These look like cotton balls, and have flat bottoms. These clouds form pretty low-from 5,000 to 6,000 fee up, and are relatively gentle. However, they are also the clouds of thunderstorms. Sometimes the right combination of clouds and wind can cause threatening clouds and conditions. A hurricane is often characterized by a gigantic swirling of cumulus clouds that reach to high altitudes.