COCORAHS – Who they are, how they improve weather forecasting and how you can become one

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DES MOINES, IOWA — It is the first thing every Iowan wants to know after a summer or winter storm: how much precipitation did we get? Unfortunately, there isn’t always a reliable report available from your town or neighborhood. The reason? Not enough COCORAHS.

COCORAHS is an acronym for ‘Community Collaborative Rain, Hail and Snow Network. It was developed by the Colorado Climate Center in 1998, the year after a significant flood in nearby Fort Collins.

“The basic idea for the network is to have a more robust precipitation monitoring network, given the increased variability that we’re seeing in rainfall events across the United States,” says State Climatologist Justin Glisan. That level of variability was also seen in the Des Moines metro during the flash flooding event in 2018.

“My cocorahs rain gauge in Beaverdale had five and a half inches in three hours. You go three miles north, anywhere from six to eight inches,” says Glisan, “So that shows you how the rainfall variability is changing. So having a broader network, with more gauges in it allows us to get a better idea of where rain is actually falling as opposed to having to interpolate between the stations.”

Rainfall, snow and hail reports are used in many ways. Local forecasters – like the WHO 13 weather team – use them to verify and improve forecasts. FEMA uses them for federal disaster declaration following snow storms. They are even used by local insurance companies to verify whether storms were present on days when damage claims were filed. In the ag sector, they can affect commodity prices as well as strategies for marketing and investment.

Becoming a COCORAHS observer is easy. Go to www.cocorahs.org, order a four-inch rain gage and register it with the network. You’ll then get to report your findings every morning at 7:00 a.m – even if there is no rain, snow or hail to report. 

“Even if we don’t get rainfall, report those zeros because that produces a consistent record, and then that data is actually put into the federal record with the National Weather Service, so we can actually use it for drought or wetness monitoring,” says Gilsan.

For the most accurate reports, place your rain gage in an area where it won’t be blocked by a tree, fence or house.

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