The effects of the simplest weather fronts and the clouds associated with them throughout the year. Warm and cold fronts are shown using the symbols made familiar by TV meteorologists; a handy cloud-classification chart shows the shape and height of common clouds. Each page includes a carefully selected photo of the sky and cloud cover, a vertical cross-section drawing of the clouds with their height in both feet and miles, and a line drawing showing the fronts. The photos were taken in an area of Maine called ``thunderstorm alley.'' An attractive, useful guide. Glossary; brief index. (Nonfiction. 10-12)