U.S. forecasters upgrade spring flood risk south of border

U.S. flood forecasters say the threat of significant flooding on the Red River south of the border this spring "has increased substantially" because of recent heavy snowfall as well as deep frost.

In its second spring flood outlook of 2019, the U.S. National Weather Service upgraded the risk of significant flooding along the North Dakota and Minnesota portions of the Red River basin from low to substantial, "running above long-term historical averages."

• Low risk of significant flood along Red River in U.S. this spring: weather service

One reason for the change is heavy snowfall in late January and throughout February. The snowpack in the U.S. portion of the Red River basin runs from just below average to well above average, wrote Greg Gust, who is the weather service's warning co-ordination meteorologist.

The second reason is cold temperatures from December through February have allowed frost to penetrate roughly a metre into the ground. This will limit the ability of soil to absorb runoff, Gust wrote.

'At the mercy of March'

The severity of flooding will depend on how much snow or rain falls during the rest of the winter and how fast the ground thaws.

"We're at the mercy of March!" Gust wrote. "Climate outlooks now indicate a later snowmelt and runoff cycle, which increases our risk for rapid and/or rainfall-enhanced runoff."

During a conference call with reporters on Friday, Gust said soil from the Grand Forks area up into southern Manitoba was somewhat dry this fall and that may help the ground soak up some water if the soil has time to thaw out. 

"We don't have the waterlogged, very wet soils that we would have had in '97, 2009, 2010 and 2011. So that certainly helps," Gust said. "But a high amount of runoff would be expected unless we get a very gentle thaw."

• Winnipeg shovels out from snowiest February in 32 years

While significant flooding along the Red River in the United States does not necessarily mean there will be similar flooding north of the border — the river capacity increases as it winds its way north — southern Manitoba has also experienced a snowy February and a colder-than-average winter.

Manitoba is expected to issue its next flood outlook within weeks.