National Weather Service warns about possible risk for spring flooding
Most river basins have an above average amount of water in the snowpack, increasing the risk for spring flooding particularly for the Bad River and the St. Louis River.
Spring flooding is highly dependent on weather conditions in March and April.
Ketzel Levens, meteorologist at National Weather Service Duluth, said that a slower snow melt reduces the risk for flooding whereas a faster melt and rainfall events increase the risk for flooding.
“Snow depth is above normal for most basins across our area, except for the Rainy River Basin where there are some areas where snow depth is around or just slightly below normal snow depth,” she said. “This is primarily over Koochiching County, bleeding over the borders into Itasca and St. Louis just a little bit.”
While there are currently no major changes, the next scheduled update will take place on March 23, 2023.
Snow depth remains much above normal except for the Rainy River Basin where the snow depth is only slightly above normal, particularly in Northern Itasca, Koochiching, and northern St. Louis County.
Levens pointed out that the Rainy River Basin currently has a gradient of snow water equivalent (amount of water in the snow pack) going from west to east.
“So on the western edge of the Rainy River Basin parts of Koochiching County, kind of very Northwest St. Louis County, we’ve only got about three to four inches of snow water equivalent,” she said. “But on the far eastern side of the Basin, along the border with the Western Lake Superior Basin, this is where we are getting values of five to eight inches.”
“How does this compare to last year? Generally we’re looking at about one to two inches less SWE (snow water equivalent) than last year,” Levens said, adding that the comparison is unclear due to more observations that were able to be done this year.
Basin areas with much above normal snow water equivalent include the Mississippi Headwaters, St Croix River, Western Lake Superior North Shore (MN), Western Lake Superior South Shore (WI), and Chippewa.
Values upwards to seven to eight inches exceed last year’s numbers by two to four inches.
“This is coming from the fact that we’ve had quite a bit of snow this year and quite a bit of that snow has been very wet snow. We’ve even had some mixed precipitation events that have added water into the snowpack as well,” Levens said.
“Some of that water has flown through the snowpack, but much of it has gotten stuck and frozen within the snowpack. So it is still liquid that is available to run off in the spring.”
Mississippi near Aitkin has the highest risk of flooding, a greater than 95 per cent chance of a minor flood.
In the Western Lake Superior Basin, there is a 47 per cent chance of minor flooding at the St Louis at Scanlon point.
Providing a spring weather outlook, March temperatures are estimated to be slightly below normal with a drier outlook later in the month. Cooler temperatures will likely delay keeping things fairly frozen, said Levens, therefore having a neutral impact on spring flooding.
Due to a warmer winter, this year’s soil has been less frozen than usual, allowing for snow melt to infiltrate through the soil.
“But that soil can also be completely saturated as well, and then act a little bit more like an impermeable surface,” she said. “we will at this point, just kind of have to wait and see what parts of April and May bring to get a better sense of just how that water’s running off.”
Elisa Nguyen, Local Journalism Initiative Reporter, Fort Frances Times