A lot of the ‘prediction’ part of the weather gets into the difficult stuff. We often use computers to make a ‘simulation’ of what the weather will end up as, based on the current weather conditions around the country, together with the winds that are attempting to blow it around. The trick is trying to figure out precisely what the weather is “Right Now”…which is near impossible to be 100% accurate because we don’t have a thermometer every 2 feet. What weather guys do is often vary the initial conditions of a computer model, and see how it affects the output of the simulation…if most ‘solutions’ to the forecast of a storm track are clustered around one certain location and intensity, then we’ll have a higher degree of confidence in the forecast. We often track the storms themselves using Radar (based at the ground looking up to see rain/snow/ice), and satellites (based in outer space looking down on the Earth to identify clouds and their movement).