The Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) is an informal science education project where volunteers and researchers work together to measure, map and track patterns of rainfall, hail and snow. Participants include students, teachers, senior citizens and anyone with an interest in the weather of their region. Volunteers use low-cost rain gauges and specially designed hail pads to collect and report data showing the frequency, quantity and spatial patterns of rain, hail and snow. CoCoRaHS has grown from a local endeavor in 1998 with a few tens of participants in Fort Collins, CO to a statewide project in 2004 with over 1000 active volunteers trained in the collection of precipitation measurements. The project is currently expanding into the nearby rural regions of WY, western, NE, and western KS where weather observations in general, and precipitation measurements in particular, are scarce and people's livelihoods are greatly impacted by changes in precipitation patterns.

In addition to providing critical information to local, state, and federal agencies (including the National Weather Service) on regional water resources, one of the strengths of the project has been the ability to provide important information to research scientists who then use the data in applications ranging from validating radar-based rain and hail estimates to regional climate studies. Another strength has been the engagement of citizens resulting in the increased scientific awareness of the volunteer participants.