Late melt helping reduce Fargo-Moorhead flood risk
The National Weather Service on Tuesday lowered the forecast Red River crest in Wahpeton, N.D. and Breckenridge, Minn. as the late spring melt improves the area's flood outlook.
The Weather Service expects to update the flood outlook for Fargo-Moorhead, an hour north of Wahpeton and Breckenridge, on Wednesday. Residents in Fargo are still pressing forward with flood fight efforts though.
In past years, major spring flooding put miles of farm fields underwater. This year likely will be different.
"I am definitely not seeing the water that we've had in major floods in the past," said Tom Richels who has managed preparations for 14 floods as an engineer based in Breckenridge. "It's substantially less."
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As a consultant for Wilkin County in Minnesota, Richels, who has 33 years of experience, has been out with a shovel digging in farm fields to check on conditions. In many areas the top foot or more of soil is thawed and saturated with water.
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"A substantial amount of our runoff is going ... into the ground," Richels said. "Being we were so dry last fall it was pretty susceptible to taking on a lot of water."
In a late March flood, the ground is typically frozen and much of the snowmelt runs off.
"I am definitely not seeing the water that we've had in major floods in the past."
But the delayed spring means the sun is at a higher angle and can more quickly thaw the soil, National Weather Service river forecast expert Steve Buan said.
"If we've thawed 12 inches of the soil, about 30 percent would be field capacity," Buan said. "So that would be about 3.5 inches of water in that layer of soil."
That means about 3 inches to 3.5 inches of the water in the melting snow are soaking into the dry soil rather than running off into rivers.
Engineer Tom Richels said that corresponds with the change he sees when he tests the water in the snowpack in Wilkin County. The most recent snow measurement he took was two days ago.
"Where I took it there was 4 inches of snow and that had about 1.5 inches of water in it," Richels said. "About two months ago that same area had a good 5 inches of water. "
The remaining snow in the Red River Valley will melt quickly later this week when temperatures are forecast to reach 60 degrees.
A HISTORICALLY LATE MELT
Buan said there's no soil moisture monitoring network in the region, so it's very difficult to predict how much of the melting snow will simply sink into the dry soils.
"We've never seen a melt on April 23rd, 24th, 25th at any temperature," Buan said. "We really don't have that historical sequence to look back to."
Buan said the current conditions mean it's more likely the Red River in Fargo-Moorhead will crest at the lower end of the range that's been forecast.
Buan said the rapid warmup might increase flood risk in the northern Red River Valley where it appears the soil is still mostly frozen.
The National Weather Service has predicted a flood range of 38 to 42 feet in Fargo-Moorhead. The record river level was 40.8 feet in 2009.
The actual crest date and level forecast should be available later this week, with a crest expected the following week.
MOVING FORWARD, CAUTIOUSLY
But Buan cautions the favorable conditions could change quickly if late April or early May brings thunderstorms and heavy rain.
Buan said it takes about a week for the Red River to rise up to it's peak.
"Then you've hit peak and it could be another two to three weeks until that river gets back down. So we're kind of susceptible for almost a month of having to keep significant precipitation away," Buan said.
Buan said right now there's no significant precipitation on the horizon, and there are signs the weather could be shifting to a dryer, warmer pattern.
Fargo and Moorhead are moving ahead with plans to prepare sandbag dikes and emergency levees to protect against a possible 41-foot river level.
"As of now we're planning to deliver [sandbags], to protect up to 43 feet," said Jeremy Gorden, an engineer with the city of Fargo. "If they need to sit out in the street and we protect to something less, that'll be great. It's easy enough to load them back on the truck and send them on their way."
About 300,000 sandbags were dropped off in north-side Fargo neighborhoods Tuesday. Deliveries will continue until Thursday.
MPR Associate Digital Producer Nathaniel Minor contributed to this report.
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