Skip to content

Volunteers take important rainfall measurements

Volunteers take important rainfall measurements

Posted: Thursday, April 5, 2012 8:00 pm

Associated Press
NASHVILLE (AP) — A volunteer effort that sprang from a devastating flood has grown into a nationwide network of weather observers whose data is used every day.
The Community Collaborative Rain, Hail & Snow network — also known as CoCoRaHS — plays an important part in collecting precipitation data and alerting the National Weather Service to significant rainfall.
Ralph Troutman, the Observing Program Leader with the NWS in Nashville, is the Tennessee coordinator. He said the state has CoCoRaHS observers in all but three counties and is recruiting more.
“The primary value is the precipitation reports,” Troutman said. “We’ve learned so much about the variability of rainfall. Our official observation points are on a 25-mile grid.”
As national CoCoRaHS coordinator Henry Reges pointed out, those official measuring points often don’t tell the whole story.
Such was the case in Fort Collins, Colo., in 1997 when flooding killed five people and destroyed 200 homes in what was described as a 500-year flood. The event provided the spark that matured into the national network of volunteers, Reges said.
A flash flood struck Fort Collins on July 28, 1997, after some parts of town got 2 inches of rain while others just five miles away were deluged with 14.5 inches.
That led Nolan Doesken, now the national director of the program, to form a chain of observers on the front range of the Rockies. It spread a couple of years later to Wyoming. And then it took off. By 2009, CoCoRaHS was operating in all 50 states. Doesken is the Colorado State Climatologist.
“We didn’t expect it to become a national project, but it just gained in popularity,” Reges said. “A lot of people just enjoy doing this kind of stuff and then the information became really important to the entities that use it.”
CoCoRaHS supplies information to the National Weather Service and cooperates with the agency extensively, but is run by the climate center at Colorado State University and is funded primarily by grants from the National Science Foundation and the National Oceanographic and Atmospheric Administration, the parent agency of NWS.
A number of users get the information it supplies. Among them are farm service agencies, soil conservation districts, municipalities and river navigation and recreation entities. Other users include mosquito control agencies, because the ponding of water that may lead to West Nile outbreaks, and golf courses.
Observers file their reports around 7 a.m. local time, online. The figures represent a 24-hour observation.
There is another way observers are important and it’s in real time. When heavy rain, snow or heavy rain threatens, they can send what is called a “significant weather report” that goes not only to CoCoRaHS, but also alerts the NWS office for their region.
“That one critical observation, where NWS did not that rainfall information somewhere upstream, could lead to the issuance of a flash flood warning,” Reges explained.
People interested in becoming observers can go to the CoCoRaHS website at to learn more and sign up. Training is minimal and can be done online. The only investment is a $30-dollar specific high capacity rain gauge. There is a short informational video on You Tube at
Troutman said a lot of observers like being part of record keeping that began in Tennessee in 1854, when the first weather observation station was opened in Clarksville.
“It’s a fun way for people to be involved with weather and their data becomes part of the historic record.” Troutman said.
In addition to rainfall, CoCoRaHS observers report snow and hail. In states where the latter data is collected, observers put down Styrofoam pads wrapped in foil and send photos of the dents or the pad itself to CoCoRaHS.
Observers are encouraged to file a hail report for hail of any diameter, whether or not they have a hail pad. Reports of hail one inch or more in diameter are helpful criteria to the NWS for issuing a severe thunderstorm warning.
Asked which Tennessee counties don’t yet have observers, Troutman said Cannon, Lake and Scott counties do not.
While he would like to find volunteers there, he would be equally glad to have more of them from anywhere. Observations have pointed out different rainfall amounts even in the same city block.
Troutman said the information the observers supply is solid. He has been comparing CoCoRaHS reports with those of trained NWS observers in the same area and the research so far is encouraging.
“It really reinforces the validity of the volunteer observers’ data.” Troutman said.
“We really, really need more observers in every state,” Reges added. “No experience is necessary. It’s fun, easy and takes only five minutes a day.”

Published in The Messenger 4.5.12