NWS warns of Grand Forks-area flood risk: ‘Risk for significant snowmelt flooding is substantial’
Recent snowfall could have a major impact on flooding this spring, according to the National Weather Service’s newest flood outlook.
Last month, the weather service said the potential of major flooding in the area was fairly low. However, snows in late January and the month of February have added a “substantial snowpack” making “widespread, above normal, runoff” is now likely, meteorologist Greg Gust said.
“The risk for significant snowmelt flooding is substantial, running above long-term historical averages across the Red River and Devils Lake basins,” he said.
The latest outlook gives a 95 percent chance Grand Forks will see a moderate flood of 41 feet and a 25 percent chance of a 46.9-foot crest.
Major flooding risk is particularly high north of Grand Forks near the Canadian border and near Oslo, Minn., according to the weather service. Oslo has a 95 percent chance that moderate flooding will occur at 35.5 feet and a 75 percent chance major flooding will happen at a 36.4-foot crest. Pembina has a 95 percent chance of moderate flooding at a 46.9-foot crest and a 75 percent chance of major flooding at 49.1 feet.
The runoff risk at the Devils Lake Basin has increased a fair amount, the weather service said.
A “somewhat above normal” rise is now expected, from 1 feet to 2 feet. A 6 inch to 1 foot rise on Devils Lake is considered about normal. The weather service noted Devils Lake currently is
about 1.5 feet lower than this time last year.
Grand Forks has received more than 55 inches of snowfall since Oct. 1, 2018. However, when it comes to potential flooding, the snow’s water content is more important that the amount itself. The higher the water content, the greater the chances of flooding, he said.
Gust said the snowpack and water content are higher than normal throughout the Red River Valley.
“This year, with the snowpack we have in place now ... we are going to have overland runoff, we are going to have ditches full, we are going to have breakout flows in areas and likely will have road water up on rural roadways (in the area),” he said.
Frost depths are much deeper than normal, Gust said. Ground in the Grand Forks area has a frost depth of about 40 inches.
The deeper the frost depth is, the longer it takes for the ground to thaw out, so something like spring rains on top of that frozen ground could increase the chance of flooding, he said.
The weather service says the area is “at the mercy of March” and the prospects for a delayed thaw and/or continued substantial snowfall into March. March is expected to stay cold but precipitation may be about normal, Gust said.
Grand Forks well protected
Leaders say Grand Forks is well-protected from major flooding within the city.
Mark Walker, assistant city engineer, said a lot of work is done behind the scenes that people don’t often recognize or see.
The city also prepares a number of slide gates at the flood wall, which is 60 feet high and 10 feet wide, so water does not flow into the pipes there and flood low-lying areas on the protected side of the wall.
The first significant step the city takes during flooding is to energize its first pump station when the river reaches about 35 feet. Typically, the first pump station energized is located near the corner of Belmont Road and 15th Avenue South. He noted all 12 of the city’s pump stations are prepared months before the potential for flooding even sets in.
One of the first things people notice is when the city closes a road to traffic, Walker said.
Closures happen at Minnesota Avenue along the Point Bridge at about 45.2 feet. The closure of the Sorlie Bridge on DeMers Avenue happens at about 45.8 feet, according to the city's flood action plan.
However, the closures may go in earlier depending on when the closures on the East Grand Forks side of the bridges are required to go in.
Walker said the weather service’s 95 prediction of 41 feet means the city may end up energizing a few pump station and it also could force a Riverside closure.
City administrator Todd Feland said it’s a team effort to keep Grand Forks protected during a flood. City engineers lead the planning while public works and water works implement the strategies.
“It’s a nice blend of Grand Forks’ team working together,” he said.
Weekend weather outlook
More snow is likely in the Grand Forks area this weekend. The weather service predicts up to 3 inches of snow for Grand Forks through Saturday morning, with areas south of town receiving slightly more.
Sunday will have the potential for a ground blizzard, Gust said.
Strong winds, up to 45 mph, are expected across the Red River Valley. Reductions in visibility are likely due to blowing snow, especially in the open country.
The next flood outlook will come out March 7.