There’s little good news in the winter forecast.
The odds favor a wetter-than-normal winter in the upper Missouri River watershed, and weather experts are advising people to brace for the likelihood of additional flooding by next spring.
“The setup is bleak, as far as I’m concerned,” said Kevin Low, a hydrologist with the National Weather Service who specializes in the Missouri River watershed.
The problem, he said, is that the Missouri River basin already is primed for spring flooding, based on late-summer conditions: overly wet soils and high stream levels. The region is more water-logged now than it was a year ago at this time, he said.
On Monday, the National Weather Service elaborated on some of the discouraging conditions that could occur by spring, including the potential for some rivers to freeze above flood stage and for flooding to freeze in place in fields. Depending upon what happens this winter, there’s a risk of “widespread ice jams, including on some rivers that are not usually affected by ice jams,” the weather service noted in an update on conditions in the Missouri River watershed.
Compounding the concern is the winter forecast, issued last week by the U.S. Climate Prediction Center. The odds slightly favor higher-than-average precipitation this winter across much of the northern U.S., according to the prediction center.
If that happens, the upper Missouri River watershed could accumulate above-average mountain and plains snowpack by spring, Low said.
Holding back runoff from upper basin snowpack is the reason that six massive dams were built along the Missouri River. Together they compose the largest reservoir system in North America. Without those dams, the river routinely flooded its valley twice a year.
Upper-basin runoff was the cause of 2011’s historic flooding, though not the flooding this year.
Those reservoirs are overly full, too. The U.S. Army Corps of Engineers has committed to getting the reservoirs back to their normal flood-storage capacity by the winter freeze. That’s why the agency is releasing water at more than twice the normal rate from the dams.
Undammed rivers north of Omaha also are running overly high. Some of those, notably the James River in the Dakotas, may not drop below flood stage between now and the start of next year’s flood season, Low said.
Seasonal forecasts are notoriously difficult to make for the interior of the continent, and meteorologists are making no bets on whether winter will be colder or warmer than normal in this part of the country.
The Climate Prediction Center’s projection for a wetter-than-normal winter is based on long-term trends in computer models, said Mike Halpert, deputy director of the agency. The last 12 months have been the wettest in 124 years of record-keeping for the U.S.
And anything can happen with the weather. After historic flooding in 2011, the region saw an intense, flash drought in 2012.
Forecasters have said a recurrence of the catastrophic flooding that occurred in March is unlikely, given that it stemmed from an extraordinary confluence of events, including a bitterly cold end to winter. The trigger was an unusually intense and massive mid-March storm that engulfed the central U.S. and unleashed heavy rains that melted a frozen landscape.
A major worry is the weakened state of the Missouri River’s levees, which were shattered this spring. The corps has said breaks in federal levees will be filled by the start of next spring’s flood season, but not all will be built back to their normal height.
The agency has said it expects it will spend $1 billion and need two more years to fully fix the levees.
Worse though, in terms of flood risk, is that holes in some nonfederal levees along the river may be left open for lack of funding to make repairs.
Damaged levees are the reason for ongoing flooding of farm fields and recent closures of Interstate 80 and Interstate 680.
In terms of temperature, there’s no clear sign of what winter may bring for Nebraska and Iowa. For all but the north-central U.S, the Climate Prediction Center said the odds favor a warmer-than-average winter. Even if winter averages warmer than normal, there are still likely to be periods of extreme cold, the center said.