Nancy Lawless, age 73, of Portland, Mich., for her question

HOW ARE CLOUDS FORMED?

A cloud's name usually describes its appearance. Cumulo means heap or pile, so cumulus clouds are piled up masses. Strato means layerlike and cirro means curl. Clouds are also grouped into classes according to their height above the ground.

Clouds can come down and press against the earth and also rise to heights of 60,000 feet.

A cloud will form when moist air rises and becomes cooler. Air can rise by convection, lifting or frontal activity.

If clouds are caused by convection, it is a result of solar radiation that heats the ground and the air next to it. The warm air then becomes lighter and convection  a flow of air  carries this warm air upward. As the air goes up, it becomes cooler. And if the air is moist, some water vapor will condense and form clouds.

warm, moist air blowing over mountains or hills is lifted to form clouds. When the air rises, it cools and cannot hold all its water vapor. The vapor then condenses ¬or changes to drops of liquid  and forms clouds over the high ground. Clouds formed with this lifting method cover the tops of some mountains almost permanently.

A third type of cloud formation can come from frontal activity. A weather front occurs when two masses of air at different temperatures come together. For example, cool air can move under warm air along a cold front. The warm air is then cooled as it rises above the cool air. Many clouds can then form along this front and at all altitudes.

A cloud can often contain both ice particles and water droplets if the temperature is between 32 degrees F. and minus 40 degrees F. Water droplets do not always freeze at the normal freezing temperature of 32 degrees but instead can remain liquid in temperature all the way down to minus 40 F.

Rain or snow forms when water evaporates from the liquid droplets and freezes on an ice crystal. The crystal grows larger until it falls out of the cloud. It will fall to earth as a snowflake unless it meets a layer of air with temperatures above freezing. If that's the case, it will then melt and come to earth as a raindrop.

Heating and cooling of the earth itself are also influenced by clouds. It's usually cooler on cloudy days because the clouds reflect much sunlight back into space.

At night, clouds help to warm the earth. The heat given off by the earth is intercepted by the clouds and much of it is sent back toward the ground. On a cloudy night, you'll discover, it is usually much warmer than on a clear night. Heat is trapped in a layer of air between the earth and clouds especially when their are low hanging clouds above the ground.