What with "scattered showers" and even more mercurial "isolated showers," a state can never have too many rain gauges.

That's the premise of CoCoRaHS, or the Community Collaborative Rain, Hail and Snow Network. It is, as billed, a bunch of volunteers who check their rain gauges each morning and report what is — and even what isn't — inside.

"Be a hero, report your zero," reads the note taped to Pete Boulay's computer in the Minnesota State Climatology Office in St. Paul. He's a climatologist with the Minnesota Department of Natural Resources, and also coordinates CoCoRaHS here, maintaining that "everyone's a meteorologist at heart."

It's a known fact that bedrock Minnesotans are buoyed by knowing how much rain fell the previous night, able to step onto any elevator and fill the conversational vacuum.

But CoCoRaHS has an even higher calling: compiling as much data as possible, which enables researchers to learn more about weather patterns, which ultimately helps farmers plant the right variety of crops, contractors use the proper building materials, and friends schedule picnics.

Karl Stoerzinger, 31, joined the CoCoRaHS network about three years ago after he began tinkering with rain barrels. He devised a system of redirecting water from a filled barrel into another, and another, instead of letting the rain in a topped-off barrel dribble away.

Karl Stoerzinger made various versions of filters to collect any debris that runs off the roof. This is one of his most successful.

"When I did the math, I was shocked at how much rain ran off a roof," he said.

How much? One inch of precipitation sheeting off a 10-by-10-foot roof can fill a 55-gallon rain barrel.

With that in mind, he sought a finely tuned rain gauge that could measure to the 100th of an inch. Searching for a source online, he discovered CoCoRaHS, which sells gauges made to National Oceanic and Atmospheric Administration standards by a company in Fergus Falls, Minn.

"I thought, 'Well, shoot, that'd be fun,' " Stoerzinger said, being part of a national network, but also being able to track how his readings compare with others'.

While rain totals always are reported by city, "there can be such different levels by neighborhood, or even street," he said. "There really is an edge to every storm."

Stoerzinger's gauge is strapped to a post with an old bike inner tube; he's a bike mechanic by trade. On a recent morning, it registered .17 of an inch of rain, which he reported on his phone via an Android app as he walked through his back yard to go to work.

"They ain't paying me nothing to be a volunteer," he said, laughing. "But they can use all the information we all can give them."

Low-tech still works

In this age of high technology, it's almost charming that a plastic back-yard rain gauge still performs a pivotal service.

CoCoRaHS began in Fort Collins, Colo., after a flash flood in 1998 revealed that there were too few rain gauges in place to track what happened, said Henry Reges, the national coordinator. He led a movement to install more gauges along the Front Range of the Rockies, which grew into more gauges being installed in nearby states.

"We just launched in the Virgin Islands this week," he said, bolstering the network of about 20,000 volunteers, making CoCoRaHS the largest provider of daily precipitation measurement in the United States.

People join "because they really enjoy having a responsibility," he said. "What's nice about this project is that your observations get used, and used in real time by so many different folks.

"The more observations we have, it's like the pixels on a photo," he said. "The more there are, the better the picture is. I think of it as a citizen science project, building more climate literacy."

The 7 a.m. check-in

CoCoRaHS networks are in every state. Minnesota actually was among the last to sign on, mostly because our inherent weather geekiness had spawned other systems, such as the High Spatial Density Precipitation Network, which also measures rainfall.

But having all states on board with CoCoRaHS enabled federal funding, so joining was the neighborly thing to do, Boulay said.

Anyone can sign up on the website and complete a brief online training program, which includes how to measure snow and make your own hail mat, although how deeply you get involved is up to you. Just reporting rain is enough.

Observers must buy a standard 4-inch-diameter rain gauge, which costs about $35.

Ideally, volunteers register their readings at 7 a.m. to give some consistency to the precip portrait. "But really, anytime between 4:30 and 9:30 a.m. is fine," Boulay said.

The gauge holds up to 12 inches of rain, he said. "If it gets to the point where it's going to overflow, you've got bigger problems than being able to take a measurement."

But deluges happen. Hokah, Minn., in the southeast corner of the state, got 15.10 inches on Aug. 19, 2007, the largest 24-hour rainfall total ever officially measured in Minnesota.

Boulay is seeking more volunteers, particularly outside the Twin Cities. But he'll accept anyone from anywhere. His pitch: "You learn a lot about the weather by doing it."

To learn more, visit www.cocorahs.org.

Kim Ode • 612-673-7185