Published: March 16, 2008 12:27 am         

Weather data providing more than a drop in the bucket

PALESTINE, Texas — Checking daily rainfall at his Lost Prairie Lake home isn’t the most time-consuming thing on Jack Coleman’s plate.

As a certified public accountant, Coleman spends much of his time these days preparing clients’ taxes.

But keeping track of, reporting and comparing his daily precipitation, whether rain, snow or hail, with others around the state has become addictive, said Coleman, who electronically shares his findings with weather researchers as part of the Community Collaborative Rain, Hail & Snow Network, or CoCoRaHS.

“The more I’ve gotten involved, the more I look at the (CoCoRaHS) Web site, the more interested I’ve become,” Coleman said.

Begun by Colorado State University researchers after severe flooding in Fort Collins, Colo., in 1997, CoCoRaHS is a grassroots effort to provide more actual precipitation data than is available from the National Weather Service reporting sites.

The organization’s goal is to have at least one weather observer every six square miles, filling in gaps left between NWS reporting sites. The organization has received grants from the National Science Foundation and the National Oceanic and Atmospheric Administration (NOAA) which have helped CoCoRaHS expand beyond Fort Collins and into 29 states.

The idea is, the more data that’s available, the truer picture available for meteorologists and researchers to see what’s really going on with storms and flooding.

“By getting more on-the-ground ‘truth’ reports, even though we’ve got a very good government radar system, it helps calibrate the radar,” said Troy Kimmel, CoCoRaHS state coordinator for Texas and a lecturer in studies of weather and climate for the University of Texas at Austin’s Department of Geography and the Environment.

With precipitation readings provided by CoCoRaHS volunteers, researchers can compare what filled rain gauges with what the Doppler and Nexrad radars estimated to see not only how accurate the radar estimates were but also how storms evolved over their life cycles.

“Radar is nice, it’s great, it’s one of the biggest advancements,” Kimmel said. “But there’s nothing like having that ground truth report, backing up the radar and supplying information to the National Weather Service.”

Meteorologist Greg Story, a forecaster for the NWS’ West Gulf River Forecast Center who also serves as the CoCoRaHS North Texas coordinator, said that the ground observations help forecasters more accurately predict flooding.

“What we have to do to make the most accurate flood forecast is know how much rainfall there is in various spots,” Story said. “Even after all the quality control efforts, it’s still just an estimate. We do direct comparisons with rain gauge estimates from CoCoRaHS and others.

“We compare the ground truth with what it was estimated to be. If the estimate is not correct, it allows us to go back and raise or lower our estimate for our (flood) forecasts. It’s a very important piece of data that will allow us to make better flood forecasts.”

In addition, as more volunteers put up rain gauges and log in their daily totals, the information may prove true something that long-time residents in certain areas had said for years — which areas seem to attract bad weather.

“There’s always that talk, ‘Oh, you don’t want to build out there.’ This precipitation data gives some idea of what’s taking place,” Coleman said, noting that he’s known storms taking a certain track seem more likely to hit his property than others. “If you look at the storm tracks, something that hits the north side of Palestine catches us.”

Kimmel agreed, recalling seeing television weather reports with data from only one or two sites.

“We’re used to seeing one rain gauge report,” Kimmel said. “For years we’ve known how much fell there but knew that another part of town was different. By filling in the gaps, we’ll get more complete ground truth.”

Becoming involved requires only a rain gauge and dedication to record amounts at the same time on a daily basis, ensuring comparable data.

“This gets people involved in weather forecasting,” Kimmel said. “It’s simple but at the same time, it becomes part of the national database. I can go back and look at rainfall amounts all over Texas.

“I’ve seen junior high and high school students involved, and people from all walks of life involved,” he added. “It’s truly satisfying.”

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Beth Foley writes for The Palestne (Texas) Herald-Press.



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On the Net:

Community Collaborative Rain, Hail & Snow Network (CoCoRaHS), http://www.cocorahs.org

National Weather Service Fort Worth Office, http://www.srh.noaa.gov/fwd/