February 26, 2020 – Jessica Brooks, a hydrologist with the National Weather Service, presented on the spring flood outlook at the February 26 Bi-State Regional Commission meeting. Spring rains and the rate of snowmelt will influence the severity of flooding, she explained, which are difficult to forecast months in advance with high degrees of certainty. However, four other factors that can be measured at present suggest long-duration flooding is possible on the Mississippi this spring.
These factors include the total rainfall amounts from the previous autumn. Fall 2019 was unusually wet, with 175% of normal accumulated precipitation recorded in the Quad Cities region and between 200% to 300% recorded in areas along the river to the north. This has resulted in extremely wet soils (above the 80th percentile for soil moisture), which is a primary contributor to above normal flood risk. Also contributing is the depth of frozen ground, which has locked in the soil moisture. Until the soils dry out, the flood risk will remain high.
There was some good news, though. A warmer winter has resulted in a somewhat shallower depth of frozen ground than normal, and above normal streamflows have persisted since last fall. The snowpack has had a higher water content than normal, but the free flowing streams have helped keep runoff from the melting snow moving downstream. Free flowing streams also mean there is little danger from ice jams on waterways like the Rock River.
Taken together, current conditions indicate a high likelihood of moderate to major flooding along the Mississippi River this spring. The rate of snowmelt and spring rains will be the key determinates in the severity of the flooding. Temperatures that toggle from high to low and heavy rains could yield quick runoff and rapidly rising waters, while a more gradual warming and a drier spring could help limit the flood severity.