FARGO, N.D. – 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 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.
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 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.
Meteorologists and disaster officials sometimes refer to major floods as “500-year” or “100-year” floods, but many argue the terms should be dropped because they’re often misunderstood to mean such a flood will occur only once in that time period.
Fargo’s second big flood fight in as many years can be largely laid at the feet of El Nino, which has affected weather nationwide. In the Upper Midwest, an unusually early warm-up meant rapid snowmelt. And with the ground still frozen, that melted snow moved quickly into streams and rivers.
Donald Schwert, a geology professor and flood expert at North Dakota State University in Fargo, pointed out that the Red River Valley is unlike most others – it’s not even much of a valley – so traditional forecasting methods don’t work very well on it.
