We found a neat little book that teaches about clouds, warm and cold fronts and how to predict the weather by watching a sequence of cloud formations. The book: The Weather Sky by Bruce McMillan. 

For instance, in winter when a warm air mass approaches a cold air mass, high cirrus clouds will first appear.

 As the warm air mass drops lower, the clouds thicken and become layered cirrostratus clouds.

This is followed by a layer of cirrostratus clouds and then a layer of alto cumulus clouds. The sky looks overcast.  Alto stratus clouds may be dropping snow that changes into more water vapor as it falls, meaning more clouds.

When the warm front finally arrives, the clouds are a solid nimbostartus cloud layer. The sky is a solid sheet of gray. It may start snowing. It will continue to snow until the clouds move on to another place or until the clouds don't have any more moisture left. Next, will appear a thin layer of stratus clouds and the sky will lighten and then clear.

You can read more about clouds here:

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/home.rxml