Stratus clouds are formed when an upward-moving current of air collides with a thinner layer of air above it, causing water drops to form. The name "stratus cloud" derives from the shape of the cloud formation, where the clouds produce one or more layers of cloud cover.
- The vertical movement of an air current
An air current takes an upward turn and begins to rise above the ground level. As the air rises, it begins to cool.
- Colliding with another layer of air
The upwardly rising air current collides with another, higher, layer of air. This meeting of the rising air current and the layer of air above it causes the higher layer of air to change in temperature and humidity. The temperature difference between the rising air current and the layer of air above it causes condensation.
- Water droplets form
Once the air current meets the layer of air above, the resulting uplift of the air current and subsequent temperature and humidity changes cause water droplets to form. These water droplets are what the stratus cloud is comprised of. Cirrostratus and altostratus clouds form at altitudes above 6,000 feet in elevation, while nimbostratus and cumulostratus clouds form below 6,000 feet.