Poring over rain: Volunteers keep track of this year's record rainfall

lfabian@macon.comAugust 30, 2013 

Bunny Nobles faithfully checks her rain gauge every morning about 7.

“I’ve always been obsessed with it, thanks to my mother,” she said Wednesday while installing a new gauge in her Twiggs County backyard. “Growing up, it was my mother that was so obsessed with the rain.”

Eighteen years ago, when Nobles moved to her husband’s family’s farm on Ga. 358, her mother back in Macon bought her a rain gauge.

“So I could tell her how much rain I got,” she said.

When the Nobles were growing corn, cotton and peanuts before the turn of this century, the information was crucial.

The drought put them out of the farming business, but five years ago Nobles was one of the first Georgians to sign up for the Community Collaborate Rain, Hail and Snow Network, known as CoCoRaHS.

Across the nation, about 18,000 people are measuring their precipitation and recording it online.

“Every time I see another observer join, I cartwheel because I know that is going to be so helpful for our forecasting,” said George Wetzel, a National Weather Service meteorologist, who helps coordinate Georgia’s network.

Currently there are about 1,000 volunteers across the state, but most are concentrated in north Georgia.

Wetzel needs more people to sign up within 100 miles of Macon, also near Perry and Cochran.

If Nolan Doeskin had his way, there would be a CoCoRaHS rain gauge within every square mile of the country.

Doeskin, Colorado’s climatologist, founded the network the year after a flash flood killed nine people and injured about 30 others in Fort Collins, Colo., in 1997.

There was no warning of the imminent danger.

“Where the worst flood damage occurred only got a couple of inches,” Doeskin said. “But nothing that they would have ever thought would produce such a flood.”

By going door to door, asking people if they had any way to track how much rain had fallen, he learned more than 14 inches had fallen in one area.

That was like getting a year’s worth of precipitation in one storm, he said.

“The National Weather Service did not know,” said Doeskin. “They knew on radar, but not near how much was coming down.”

Through the network, Doeskin pulled up Nobles’ precipitation readings on his computer in the Climate Center of Colorado State University.

He can track all her readings since she signed on in 2008.

On Dec. 11 of that year, Nobles recorded 4.58 inches, her rainiest day on record.

“That’s her only time over 3 inches, which is surprising,” he said.

Not to Nobles.

“Macon can get 4 inches and I can get nothing,” she said while recording her zero for the day. “This area doesn’t get as much rain.”

Like all CoCoRaHS volunteers, Nobles tracks rain to the hundredth of an inch.

She uses an official gauge that consists of a plastic tube, 4 inches in diameter and about a foot tall.

A 1-inch cylinder fits into the middle and a funnel on top secures it in place. The outer tub collects rainfall over an inch that spills over from the inner tube that is calibrated to the hundredth of an inch.

The gauge comes with a mounting bracket, so the outer tube can be removed to be emptied.

In his research, Doeskin found this type gauge was the cheapest, most accurate way to measure rainfall, and it was comparable to the NWS official model that is twice as large and much more expensive.

The CoCoRaHS gauge sells for about $30 with shipping.

The funnel minimizes evaporation, more efficiently catches blowing precipitation, including snow and hail, and keeps drops from bouncing out of the gauge.

A variety of gauges are available at stores, but ones with smaller openings will be less accurate as raindrops vary in size, he said.

The larger the sampling area, the greater the precision.

“With a gentle winter rain, you’ll be OK. But with a summer storm with big, honking raindrops, you’re going to get random differences in how many raindrops happen to fall into that area,” Doeskin said.

As Georgia’s go-to CoCoRaHS man, Wetzel can guide volunteers to the proper placement of the gauges and help them create their own weather station.

He also troubleshoots problems.

His friend could not figure out why he was getting so much rain, so Wetzel made a house call.

“His neighbor’s sprinkler was hitting it and he didn’t know that because the sprinkler worked at 3 a.m.,” he said.

Gauges should be placed in open areas, away from buildings and trees, which can be tough in Middle Georgia.

As a general rule, a gauge should be as far away from a tree as the tree is tall. If there is a 15-foot tree, the gauge should be 15 feet away from it. In an open area, double the distance from an object.

Avoid hanging it on a fence, as an updraft will affect the rainfall total. Placing it on top of a deck could result in raindrops splashing up into the gauge.

The best practice is to mount it on a post. If you use a 4-by-4 piece of wood, cut the top of the board at an angle to prevent splashing.

The National Weather Service has backup gauges near its official data collecting sites, but Wetzel said having accurate readings from volunteers will help if technology fails.

They have been able to supplement information into climate reports that had missing data.

Plus, reports during significant storms can help forecasters issue life-saving warnings.

Observers are asked to supplement their regular daily readings in heavy downpours.

“Any storm can actually produce a distinctive amount of rain, 5 to 6 inches, in one storm here, while 5 miles away, again nothing,” he said.

To learn more or order a gauge, log onto www.cocorahs.org.

To contact Liz Fabian, call 744-4303.


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