3-week period could be crucial for flood crest
The top 10 biggest floods ever recorded in Fargo-Moorhead have come in a three-week "magic time" window from late March to mid-April when spring comes in a rush to the Red River Valley, National Weather Service records show.
It's a problem typical of rivers that flow north like the Red, experts say.
"When spring arrives here, it arrives more or less all at once," said Donald Schwert, a professor of geology at North Dakota State University.
Last year's record-breaking 40.84 feet crest at Fargo-Moorhead came on March 28, and thanks to warm rains, it was sooner and faster than expected.
The No. 2 highest crest recorded was 40.10 feet recorded on April 7, 1897, and the third-highest crest was the 39.57 feet of April 17, 1997.
The top 10 crest that came latest is ranked No. 9 with 34.93 feet on April 19, 1979.
Schwert said spring sun melts the snow in the southern valley first, and as the thaw works its way northward, so do floodwaters.
"That's one factor that makes the Red River so vulnerable to flooding," he said. "You have the waters being delivered from the south meeting the waters being delivered off the landscape."
That has a multiplier effect on flood levels, which is exacerbated by ice jams.
Early April is historically "the magic time with the thaw" in this area, Schwert said. Once the snow cover leaves, the thaw moves fast.
"You add a nice rainfall or two to that, and all of a sudden, we have a pretty good flood going," he said.
Schwert said valley residents have one advantage: The area's floods are usually predictable through snowpack and soil moisture measurements.
Vince Godon, a meteorologist with the National Weather Service in Grand Forks, said the next flood forecast is due today.
There are too many variables and the thaw is too far out to make an accurate flood forecast yet, Godon said.
Something that would help is getting more volunteers to take snow depth measurements, particularly in "critical areas" between Fargo and Wahpeton, N.D., and along the Wild Rice River, he said.
"Good snowfall and water equivalents" make for better forecasts," Godon said.
Schwert and Godon encourage homeowners in flood-prone areas to take advantage of this year's warnings to buy flood insurance. The insurance must be in place a full month before it takes effect, they said.
"Take heed of the warning, homeowners!" Schwert said.
Like everyone else, he's hoping for a slow thaw - warming during the day and freezing at night - which should lower the flood crests.
"But be prepared. A warm rainfall, could lead to an event very similar to that of 2009 or 1997," Schwert said.