A new community weather network is helping to measure Arizona’s rainfall totals in an effort to improve weather data and research across the state.

Arizona is the 48th state to join the Community Collaborative Rain, Hail and Snow Network, called CoCoRaHS. Nancy Selover, ASU research professor and the Arizona State Climatologist, helped bring the program to Arizona.

Selover said the CoCoRaHS extension into Arizona provides much-needed assistance to a region with a sporadic amount of rainfall and few methods of measuring it.

“We always say every drop counts,” Selover said. “There are places where, within a mile, you’ll have well over an inch of rain and then less than 1/10 of an inch.”

Measuring these levels using a widespread network can help more accurately record rainfall as well as predict storm patterns, she said.

Volunteers first sign up through the CoCoRaHS Web site, where they are directed to buy a standard 4-inch diameter plastic rain gauge that measures at each 1/100 of an inch.

Once they take measurements with the gauge, observers can enter their daily calculations online.

Selover said she tries to adapt to the specific needs of a diverse pool of observers.

Two observers don’t have Internet access, Selover said, so they call her directly and leave voicemail messages with their observations. She enters their calculations every morning along with her own.

“We want to be fair to people, and we also want to include people who need a little help,” she said.

The cost of a standard rain gauge, at $23, may be a problem for some, Selover said. She hopes to curb this cost in the future through sponsorship.

CoCoRaHS also provides a training session for new observers, helping them to locate the best place for their rain gauge and to take more accurate measurements.

Observers range from retired Arizonans to elementary students working on classroom projects to people Selover refers to as “weather geeks.”

That’s where CoCoRaHS provides an unexpected service — social networking.
“Whether we call ourselves ‘weather geeks’ or ‘weather weenies,’ people who observe weather really like to talk about the weather,” she said.

Following training sessions, Selover said participants often share their observations, predictions and thoughts with fellow “weather geeks.”

As of Sept. 21, the program had 358 participants registered. But Selover said that though many may sign up for the program, not all observers commit.

“If you get about 50 to 60 percent active observers, you’re doing well,” she said.

States like Colorado, where CoCoRaHS first started, have an estimated 300 to 400 active observers.

Matthew Pace, a graduate student in meteorology and climatology and a weather observer for CoCoRaHS, said the network is an important tool for improving public safety.

“It’s important to get an accurate distribution of rainfall since we have such scattered storms,” he said. “We can help the National Weather Service issue flood and flash-flood warnings and get the information out to the public.”

Pace said ASU students in particular can help enrich the process.

“It would be nice to see more students involved, especially if they live in Tempe, so we could get a more dense network,” he said.

Valerie Meyers, a meteorologist with the National Weather Service, said CoCoRaHS helps advance the weather service’s outreach.

“Public networks like CoCoRaHS really make our products and services much better,” she said. “The human eye and the human element are very valuable.”

Reach the reporter at jessica.testa@asu.edu.