FARGO, N.D. - A year ago, 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 an 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 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 flood stage on Sunday.
Fargo resident Richard Thomas, 61, 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 with a special water-filled tube. He's got it on standby if crest levels go higher this year.
The record-high water of 2009 helped forecasters by supplying 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.
Recent history in the Red River Valley has been painful for the weather service. In 1997, forecasters knew there would be record flooding on the Red River in 80 miles north of Fargo in Grand Forks, but they didn't realize just how bad it would be in time for the city to build its dikes high enough. The Red swelled to a record 26 feet above flood stage and the defenses failed, forcing most of the area's 60,000 residents to evacuate.
Last year in Fargo, after forecasters belatedly increased their crest prediction to 25 feet above flood stage, the city raced to pile its sandbags higher. The estimate proved to be about 2 feet too high, though the dikes held when the Red topped off.