Probability of moderate to major flooding has been reduced since Feb. 27

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By Ted Pennekamp

 

According to the latest Spring Flood Outlook issued by the National Weather Service on March 12, the overall probability for flooding along the Upper Mississippi River is above normal this spring but the probability for moderate to major flooding has been reduced significantly since the last outlook of Feb. 27. The potential for flooding along Mississippi tributaries is now around normal to slightly above normal. Precipitation this spring will be key in determining how the flooding potential evolves.

Nearly 5 to 25% of normal precipitation fell across the Upper Mississippi River basin since the latest update to the Spring Flood Outlook. Midwestern Minnesota was the driest area with only 1 to 2% of normal precipitation. All across Iowa, southern Wisconsin, southern Minnesota and northern Illinois saw well below normal precipitation. As far as temperatures go, most of the area was 2 to 3 degrees above normal across Minnesota, Wisconsin and northern Iowa.

Large ice dams in all of the pools of the Upper Mississippi River this winter, especially in pools 6 and 10, had helped to produce high river flows throughout the winter that raised concerns about flooding. Those ice dams, which had held back significant amounts of water, have now all been broken up and melted, said Dan Fasching, Upper Mississippi River water manager for the U.S. Army Corps of Engineers, St. Paul District.

“The ice dams broke up and enough water drained so that we got down to normal for a couple of days in Pool 10,” said Fasching. “Then we had some snow melt so the river has gone back up.”

Fasching said the river stage was below 613 feet (relative to sea level) at the Clayton Gauge at the beginning of March, which was good.

“We’ve been really lucky,” said Fasching. “The snow in Minnesota and northern Wisconsin has been melting slowly, and there has been no more snow and not much rain.”

As of March 16, the river stage at the McGregor Gauge in Pool 10 was at 12.98 feet and is predicted to reach 13.6 feet on March 20.

“We’ve had a good slow snow melt which is helping a lot,” said Fasching. “We’ve been really blessed the last month.”

Fasching said all gates at Dam 9 near Lynxville and Dam 10 at Guttenberg were pulled on March 12 and have been wide open since.

Fasching also noted, however, that there is still a good amount of snow in northern Wisconsin and northern Minnesota, including in the area of the Mississippi River headwaters at Lake Itasca, Minn. The average depth is about 6 to 8 inches with deeper amounts in northern Wisconsin where depths of 18 inches and greater are common. This continues to be near to above normal for this time of year.

In addition, he said the snow a few weeks ago had a water equivalent of 4 to 6 inches, which is a hearty amount. According to the  National Weather Service, the  water content in the snow in the Mississippi River contributing portions of Minnesota and Wisconsin was 2 to 5 inches on average as of March 12. Across central Minnesota, liquid equivalents ranged in the 2 to 3.5-inch range. Overall, the amount of snow water content remains above normal in the northern regions of the Upper Mississippi River drainage area.

The snow pack has melted across northeast Iowa, southeast Minnesota, and much of southwest Wisconsin. 

The melting snow pack of northern Minnesota and northern Wisconsin will continue to make its way into the Mississippi, Wisconsin, and Black Rivers over the next few weeks. Stream levels remain elevated for this time of year across much of the area and soils are wet. So, the soil and stream conditions are favorable for flooding potential. Soil moisture conditions as reported from the Climate Prediction Center continue to be well above normal across Minnesota and Wisconsin which are mostly in the 95th percentile.

Monthly average stream flows across the Upper Mississippi River basin remain above to much above normal with many stations in the “high” category according to the U.S. Geological Survey. These stations are located mostly within Minnesota, Wisconsin and northern Iowa. “High” indicates that the estimated stream flow is the highest value ever measured for that day of the year. Frost depths within the drainage remain to be near to below normal.

The major flood potential has decreased from St. Paul, Minn. to near La Crosse since the last Spring Flood Outlook update. The fact that the significant snow pack is confined to northern Wisconsin and northern Minnesota has lowered the likely crests along the Upper Mississippi by two to three feet, according to the National Weather Service which will continue to closely monitor observed and forecast weather conditions. Conditions over the next few weeks or so will be key in determining just how the flooding situation evolves.

Area residents are encouraged to continue to monitor river forecasts and weather forecasts closely if they live near or have interests along rivers and streams.

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