Cumulus clouds are normally flat on the bottom and fluffy on top. They are commonly found below 6,000 feet but can sometimes be found at higher altitudes. Cumulus clouds are not usually signs of precipitation, but they can sometimes form thunderheads. It is more common to see cumulus clouds floating overhead with bits of clear blue sky between the clouds.
Cirrus clouds are commonly found at higher altitudes usually above 10,000 feet. They blow across the sky from west to east, and the wind blows them into long wisps. Blue sky can usually be seen between the wisps that often form a curl at the end. They are nicknamed mares' tails because of the long wisps that they form. Cirrus clouds can also combine with cumulus and stratus clouds and create more thin and ripply clouds in the sky.
Stratus clouds are flat and can be white or gray. They often cover big areas in the sky and may even block out the sun enough to make it hard to determine where it is located in the sky. Stratus clouds often represents an overcast or rainy day. They most commonly occur below 6,000 feet but can be found at higher altitudes. Fog is a form of stratus cloud that occurs near the ground.
Nimbus clouds are clouds that produce precipitation. These clouds will start out as cumulus or stratus clouds. Cumulonimbus clouds are thunderclouds that produce thunderstorms with common downpours of rain or other precipitation. Nimbostratus clouds will produce steady rains or snow that are not accompanied by thunder and lightening.
The names of the clouds can be mixed to represent specific situations such as; cumulonimbus which refers to cumulus clouds that produce precipitation or stratocumulus clouds which form in rows or patches. Alto is a prefix that is used in combination with cloud names. It is used to describe clouds that are higher in altitude. Alto clouds are usually found to range from heights of 6,000 feet to 20,000 feet.