The Community Collaborative Rain, Hail & Snow Network (CoCoRaHS) is a non-profit, community-based network of volunteers of all ages and backgrounds working together to measure and map precipitation (rain, hail and snow). By using low-cost measurement tools, stressing training and education, and utilizing an interactive Web site, the network's aim is to provide quality data for natural resource, education and research applications.

Volunteers post their daily observations on the CoCoRaHS Web site. Observations are immediately available on maps and reports for the public to view. By providing high quality, accurate measurements, the observers are able to supplement existing networks and provide useful results to scientists, resource managers, decision makers and other users.

CoCoRaHS came about as a result of a flash flood that hit Fort Collins, Colo., in July 1997. A very localized storm dumped more than a foot of rain in several hours while other portions of the city had only modest rainfall. The ensuing flood caught many by surprise and caused $200 million in damages. CoCoRaHS was born in 1998 with the intent of doing a better job of mapping and reporting intense storms.

As more volunteers participated, rain, hail, and snow maps were produced for every storm showing fascinating local patterns that were of great interest to scientists and the public. By 2010 CoCoRaHS became a nationwide volunteer network.

The National Oceanic and Atmospheric Administration (NOAA) and the National Science Foundation (NSF) are major sponsors of CoCoRaHS.