CoCoRaHS

What is CoCoRaHS?

CoCoRaHS stands for the Community Collaborative Rain, Hail, and Snow Network. It is a volunteer network made up of people just like you who report the precipitation that falls in their own backyard! Like the name implies, they report rain, hail, and snow!

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​Map of 1997 Fort Collins, CO flash flood. At point A, nearly 15 inches of rain fell. At point B, which is only about five miles away, less than 2 inches of rain fell. Five people were killed and millions of dollars in damage was done. ​(Click the images to enlarge)

Can you think of a time when you got a lot of rain, but someone you know relatively close by barely got a drop? Or how about a time you received little snow, but a location a couple miles away received a lot more? This happens all the time as precipitation is highly variable and can vary a lot even over short distances!

CoCoRaHS was founded in 1998 in response to the July 27, 1997 Fort Collins, CO flash flood. The rainfall was localized primarily on the west side of the town which received nearly 15 inches of rain in just 30 minutes. But just five miles to the east, only light rain was observed. This flash flood event was not reported to the local NWS office, and five people were killed. This event highlighted the need for a high-density, high-quality precipitation network that can be used in real-time. Thus, CoCoRaHS was born! Over the years, observers all across the country have been helping meteorologists, researchers, educators, and more by submitting their precipitation reports.

CoCoRaHS first came to Tennessee in April 2007, and over the years we have welcomed hundreds of volunteer weather observers. Today, over 200 people across NWS Nashville's area are active CoCoRaHS observers.

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CoCoRaHS precipitation map highlighting where the highest rainfall totals were on August 21, 2021 or the day of the Waverly flash flood event. (Click image to enlarge)

Daily precipitation reports help NWS Nashville meteorologists with event analysis by being able to map out where the highest rain and snow totals fell across the area. We can also use CoCoRaHS data in real-time to aid in warning operations! When submitted, hail reports come to the NWS office immediately which can let forecasters know whether or not a thunderstorm is severe. Significant weather reports also come to the NWS office in real-time which gives vital information in whether or not heavy rain, flooding, or even heavy snow is occurring at the time.

A significant weather report issued by a CoCoRaHS station near Brentwood on May 1, 2010. This station received over 8 inches of rain and highlighted extreme flash flooding at their location. (Click image to enlarge)

A hail report issued by a CoCoRaHS station near Green Hill. This station reported quarter to ping pong size hail on February 28, 2021. (Click image to enlarge)

Please feel free to reach out with any CoCoRaHS questions to NWS Nashville meteorologist and Middle Tennessee CoCoRaHS Coordinator Alyssa Clements at alyssa.clements@noaa.gov.