This product displays radar derived precipitation estimates that are calibrated using actual rain gauge observations. This is helpful because the radar data has important shortcomings due to how the radar works. The algorithm used to display the radar-derived precipitation data assumes the radar beam is intercepting every bit of falling precipitation and that every bit of precipitation intercepted by the radar beam makes it to the ground. Both of these assumptions are valid near the radar however they become progressively more of a stretch as you head farther away from the radar tower and higher up into the atmosphere. Rain gauge observations can fill this gap and turn unreliable data into information you can depend on.
