h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Clouds aren't solid..they are just like big areas of steam? But they are subject to tremendous forces by air currents but seem to maintaintheir shape pretty well. How does that work then?

Ah... but they don't
If you sit and watch clouds they are contantly changing.

Keep in mind that they are _in_ the moving air, as well, so if it's all moving with the same direction and speed then they are subject to little distorting force. Analogy: When you're in a car with all the windows closed, the air inside the car is moving fast but you feel no wind because you're moving at the same speed.

What a perfect analogy - that's that cleared up then

Clouds aren't really held together by anything. A cloud entering dry air WILL dissipate. The fact that clouds are in single pieces is because of the way that they form. When warm, moist air enters an area of cool air, it cools down. When it cools down it can hold less moisture. The moisture begins to condense, and you have a cloud. The edge of a cloud is simply the edge of what used to be the warm air. When the air around a cloud can hold more moisture than it already has, the cloud will evaporate. Have you ever seen a day when the edge of the clouds is fuzzy? Those clouds are evaporating. On a day when the edge of the cloud is sharp, the cloud is still forming. As long as the air around a cloud is at 100% humidity, the cloud will not evaporate.