No guarantees in forecasting floods | NevadaAppeal.com

No guarantees in forecasting floods

FARGO, N.D. (AP) – A year ago, weather forecasters changed their estimate late in the game of just how high the Red River would rise, stoking an 11th-hour sandbagging flurry in Fargo that proved unnecessary in the end because the new prediction was wrong.

Now, as the Red swells again toward an expected crest on Sunday, tens of thousands of Fargo residents are weighing the latest National Weather Service forecasts, well aware that predicting what happens on the river is anything but an exact science.

Forecasters analyze a numbing array of factors when making their predictions. Hydrologists use computer models that account for soil moisture, frost depth, snowpack, temperatures, rate of snowmelt and more. Then there are the unknowns like how much rain might spill into the river.

All of these play out over thousands of square miles of Red River Valley so flat that the flooding here can best be described as spilling a glass of water on a pool table. On Friday, the weather service changed its crest level prediction again, lowering it a half-foot to 19.5 feet above the flood stage on Sunday.

“I think they do a wonderful job, provided that they’re looking into their crystal ball with all the wisdom they have,” said Fargo resident Richard Thomas, 61.

Thomas – for now – is not too worried about flooding, with a home that sits 2 feet above Sunday’s projected crest. A year ago, he weathered the crest of nearly 23 feet above flood stage thanks to a special water-filled tube. He’s got it on standby if crest predictions go higher this year.

The record high water of 2009 helped forecasters by giving them new data on how the river behaves at those levels, said Greg Gust, warning coordination meteorologist at the weather service in Grand Forks. That makes the weather service more confident this year, he said.

“I wouldn’t say we’re relaxed,” Gust said. “We’re more relaxed, or less hectic than other years, and that’s simply because the planning process has enabled us to get some more things in place.”

Gust said forecasters have been getting a better handle since 1997 on how to predict flooding. That disaster ripped out many river gauges, Gust said. Much of the replacement equipment is stronger and less vulnerable, and the data often flows via satellite instead of fragile phone lines. Forecasters also have developed better ways of determining the mathematical probabilities of flooding, Gust said.

Knowing those odds, helps people make better dollars-and-cents decisions. Gust pointed to Fargo’s decision a few weeks ago to try to stockpile 1 million filled sandbags ahead of time, which gave the city a head start when a stretch of unusually warm weather accelerated flooding projections.

Thanks to increases in computing power, Gust said, forecasters can run alternative scenarios fairly quickly, something they couldn’t do in 1997.

“Every year there’s a different wrinkle that shows up on the terrain,” he said.