Clouds are classified by different levels: high, middle, low and towering.
High clouds, known as cirrus clouds, are thin, feathery and hair-like. They are too thin to produce any precipitation, and can often precede a low pressure system. They can also produce a halo around the sun and moon. Mid-level clouds are known as altocumulus clouds, which make for a pretty sky cover.
Low clouds, known as stratus clouds, produce fog. Fog is a cloud at ground level that can occur during the summer when warm, humid air moves over cooler ocean waters. It can also form when warm, moist air moves over a cold snow cover.
This can have a large impact on travel, especially affecting the vision of airplanes landing and taking off. Stratus clouds can produce drizzle, but not rain, because the water droplets are not large enough to do so. These clouds occur when the temperature cools to the dew point, which causes the saturation to form the stratus clouds.
When the sun hits the ground, the warm air rises, and as it rises, it cools. It eventually cools to the dew point, which causes saturation, and this continued process eventually transforms a cumulus cloud into a big cumulonimbus cloud (‘nimbus’ means rain). A cumulus cloud is not as large as a cumulonimbus cloud, which makes it difficult to produce rain, and in turn making the cumulonimbus cloud’s raindrops bigger.
The cumulonimbus cloud is towering cloud with a flat, anvil top. This is caused by the air diverging (spreading out) at the top of the cloud. Convergence (air coming together) occurs at the base of the cumulonimbus cloud. This cloud produces thunderstorms, which if severe, could form a tornado. A tornado is a funnel-shaped cloud that reaches the ground, but sometimes a funnel cloud may stay aloft and never actually reach the ground.
In conclusion, clouds are caused by warm air rising from the heat of the sun. When this warm air rises, it cools due to expansion. It eventually cools to the dew point and totally saturates the air, forming clouds. Second clouds also form when the temperature cools to the dew point, only there is no upward vertical motion to the air. An example of this is the formation of stratus clouds. Because there is no upward vertical motion to stratus clouds the water droplets in these clouds are not large enough to cause rain.