National Weather Service releases first spring flood outlook

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CEDAR RAPIDS, Iowa (KCRG-TV9) -- The risk of spring flooding on local rivers is forecast to be near to above normal, according to this season’s first flood outlook. In particular, the Mississippi River has a greater than normal chance of experiencing flooding. The tributary rivers, such as the Cedar and Iowa, have a near normal chance of flooding when compared to historical records.

Several factors affect the likelihood of flooding. This outlook is based on current conditions and the forecasts of general trends over the coming weeks not just in eastern Iowa, but upstream in Minnesota and Wisconsin.

Soil moisture across northern Iowa into Minnesota and Wisconsin is among the wettest observed for late winter. This is mainly from the heavy rain that occurred last fall that was then “locked up” during the winter when the ground froze. Wet soil, like a sponge, has a harder time absorbing more water; heavy rain falling on wet soil increases the risk of flooding. Soil moisture in southern Iowa is near or slightly below normal.

Frost is not as deep as normal. In areas that would affect our rivers, the frost is four to 20 inches deep. More specifically, northeastern Iowa has frost down to about a foot into the soil. Since the frost is not very deep and will continue to thaw because of the mild temperatures coming up, frost depth will not add to the flooding risk this spring.

Streamflow, or the amount of water coming through the rivers, is running above to well above normal. The volume of water increased due to the rains last fall, and the wet January and snowmelt since then has kept them running high. Since rivers are carrying more water than normal, it won’t take as much to push them into flood stage.

The snowpack in eastern Iowa and north has melted away over the past couple of weeks and the existing snowpack is less than normal for mid-February. Very little is left in Iowa, and what remains upstream in Minnesota and Wisconsin will be melting. Generally, less than two inches of liquid remains in the deepest remaining snow although there are still isolated spots with more than that. Snowmelt may be a factor for flooding on the Mississippi River since its basin is very large, but it should not contribute to the flooding risk on tributary rivers.

The Climate Prediction Center has not identified any obvious weather patterns that would suggest higher odds of temperatures or precipitation being above or below normal in March. So, there are “equal chances” of both of them being above, near, or below normal. The three-month outlook for March through May does indicate higher than normal odds of temperatures being above normal, while the odds of above-normal precipitation are slightly higher than normal.

The next flood outlook will be released on Thursday, March 2.