Spring flood outlooks have some variability for 2020. Some details from the lower Missouri-mid Mississippi flood outlook issued by the National Weather Service River Forecast Center in St. Louis, Missouri on March 12, are noted here.
The larger rivers, particularly the Mississippi and Missouri rivers, have experienced well above normal streamflow through most the past winter. This is providing a high starting point for these rivers to accept future runoff.
In addition, in the wake of last year's historic flooding along both rivers, soil moisture in both basins remains very high, particularly across the upper Midwest and Northern Plains. This will prevent the land areas from absorbing much future snowmelt or rainfall, and this situation will not change until after the spring thaw, when prolonged warm and dry weather may provide an opportunity for these soils to dry out.
Snow water equivalent in the upper Mississippi River basin is the biggest change in this updated outlook from last month. In mid-February, several inches of snow water equivalent was in place across much of northern Iowa, northern Illinois, and all of Wisconsin and Minnesota. Today, that significant snowpack is confined to only northern Wisconsin and northern Minnesota. This has lowered the likely crests along the upper Mississippi by 2 to 3 feet. Along the Missouri River, moderate flooding remains likely at Jefferson City and Hermann, and minor flooding remains likely at Chamois, Washington, and St. Charles.
This update represents an increase in expected crests along the lower Missouri River, likely due to a higher starting point this week resulting from the current minor flooding. While there has been some lowering of likely flood crests along the Mississippi, the final determinant to the severity of spring flooding will be basin-wide rainfall in all Missouri stream basins.
Most streams in Missouri have a likelihood of seeing minor flooding over the next 90 days. In Illinois, the Illinois River and La Moine River are also expecting above normal chances of flooding this spring. On the Kaskaskia River, flood chances are close to normal at Vandalia, but this means minor flooding is likely at this location.
While the bi-state region is largely devoid of significant snowpack, high soil moisture and abnormally high streamflow, particularly south of the I-70 corridor, are contributing to flood chances in these local basins.
Bryce Anderson can be reached at email@example.com
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