Water plays an important role in weather, not only as a liquid in rivers, lakes, oceans, and clouds, but also as a vapor in the atmosphere and as a solid in snow, glaciers, ice, and clouds. The total quantity of water in all forms in Earth’s hydrosphere can be considered to be constant, even as water moves through the environment, changing phase from liquid or solid to vapor and back to liquid or solid again, in a process called the hydrologic cycle, or water cycle.

This Reading provides background information on the underlying concepts in the Activities included in the Project Earth Science: Meteorology, Revised 2nd Edition. The Reading goes beyond what is found in the background information in the activities. The Reading can be used as supplementary information for the teacher, or to enhance classroom discussions.