One of the great wonders of the universe is that our planet is surrounded by a unique blend of compounds, including water in its vaporous state. Actually, water is pretty big on the surface of our planet itself. More than 75 percent of the earth's surface consists of water. Maybe this should be called planet Ocean rather than planet Earth. There really is water everywhere, and the big forecasting challenge each day is to determine whether some of that invisible vapor will transform into falling rain. "To rain, or not to rain …" really is the question weather forecasters deal with daily.