When you hear rainfall reports, you might wonder where they originate. There a number of different methods. One of the most common is the National Weather Service Cooperative Observation network. This system has been in place since the 1860s. Individuals go out daily and measure the rainfall, and in many cases the snowfall. They use a standard 8 inch manual gauge to report and record their observations. A more recent network is CoCoRaHS – Community Collaborative Rain Hail and Snow network. In operation since 1998, it is also a network of volunteers using a standard gauge, and reporting on-line. Finally, there are a number of automated gauging systems, including ASOS, and Kansas Mesonet. All systems are working to answer the question: How much rain DID we get last night?
Mary Knapp, Weather Data Library