Spring Flooding Outlook

Weather

Some good news with this year’s spring flooding outlook! The risk this year is down quite a bit from what it has been the past few years.
Looking specifically at the Mississippi River at Rock Island, this year’s likelihood on major flooding is at 25%. This is significantly lower than last year when it was at 95%, and 85% back in 2019.

This risk for smaller water sheds downstream of the Quad Cities is at a higher risk. The Mississippi River in our area is at a lower risk overall this year.

Factors to that this year is the layout of the snowpack, the water equivalent, and the soil moisture, and temperatures this winter.

Starting with the snow pack this year versus last year.
This year the heaviest totals of snow this year is mainly over Eastern Iowa, Northern Illinois, and Southern Wisconsin. The darker blue shows deeper snow depth with lighter shades of blue to the south of Galesburg.

Snow Depth Analysis from the Office of Water Prediction

When melted away we are left with the water content of the snow pack. This year over those areas the amount of water siting on the ground is around 2 to 4 inches.
Compared to last year the heavier amounts of water was well off to the North of the QCA with some spots along the Mississippi River watershed having water content amounts near 10 to 12 inches of water.

Snow Pack Water Content for 2021
Snow Pack Water Content for 2020

This will cause greater risks of flooding downstream of the Quad Cities, but for areas North of the Quad Cities the flooding risk is down considerably.

Other than the snow pack, soil moisture and frost depth is much better this year. This will help absorb a lot of the melting snow instead of letting it all runoff into the rivers and rising the water levels dramatically. Last year the soil was much more saturated and stream flow was much higher due to more runoff and more rainfall to the North of the QCA.

Soil Moisture from Average

This map shows areas north of Highway 30 slightly above normal for the calculated soil moisture, this will pose a slight risk for excess water to flow into the waterways but with streamflow in our area near normal it’s likely the rivers will be able to handle the extra water from spring rain/snowmelt. Especially compared to last year our stream flow is considerably better.

Stream Flow Averages

The main risk we can see for flooding will be ice jams. This is when chunks of ice block up the flow of waterways and can cause areas of localized flooding, especially for river communities.
Temperatures in February have been significantly colder than January. This has made the ice more widespread and thicker on the Mississippi River and other waterways this month. The cold snap we are experiencing now and the chance for several more days of really cold weather will continue to pose a treat for the ice to continue to thicken. This will become a greater issue when the warmer temperatures return, especially when the 2 to 4 inches of snow melt is introduced to our waterways.

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