The National Weather Service is increasing the flood risk along the Red River because of the delayed spring melt, and recent snowfall.
According to its latest projections, there is a 50 percent chance the Red River will reach 40.3 feet. That's two feet higher than the most recent flood outlook and just below the record flood of 40.8 feet in 2009.
As a crest of 38 feet is about the minimum expected, and 42 feet the probable maximum, the Fargo-Moorhead area should prepare for a flood of record, National Weather Service forecaster Greg Gust said.
"And that's taking in to account there could be at least one more heavy precipitation event coming up here," he said.
Fargo officials say they will build sandbag dikes to 44 feet to protect against a 42-foot flood. The city's sandbag-filling operations will resume Thursday to prepare an additional 500,000 sandbags.
"This is uncharted territory... Heavy precipitation has occurred and is expected to occur. Snow water that is out there right now is sufficient for a big flood."
Most permanent levees built in Moorhead and Fargo since 2009 are constructed to an elevation of 44 feet.
Gust said because the spring melt is so late this year there is no longer any historical flood data for comparison. The latest crest from spring flooding in Fargo-Moorhead occurred April 19.
This year's flood crest will likely be two weeks past that date, Gust said.
"This is uncharted territory," he said. "Heavy precipitation has occurred and is expected to occur. Snow water that is out there right now is sufficient for a big flood."
Gust said the late spring creates two big unknown factors: temperatures could warm rapidly into the 60s, and late April and early May often bring heavy rain.
"Thursday we're expecting a fairly significant band of snow," he said. "We are expecting upwards of a half inch or more of moisture back in to the southernmost part of this basin. That is figured into this calculation. What isn't figured out is how dramatic and how much precipitation really could occur out there."
Gust said rivers should start flowing late this week or early next. When the rivers crest and how high they get will depend on weather conditions over the next two weeks.
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