New outlook shows threat of spring flooding remains high
The National Weather Service released its second spring flood outlook of the season on Thursday. It shows that the risk of spring snowmelt flooding is considerably higher than average, especially on the Mississippi River. This does not necessarily mean the flooding will be major; you can see the current odds of minor, moderate, and major flood stage compared to historical odds below.
The snowpack locally has continued to melt, but there's still an inch or two of liquid in the snow in northern Iowa. Farther north in the headwater region of the Cedar, there’s a few inches of liquid. In the northern reaches of the Mississippi, the snowpack still holds over four inches of water.
Soil moisture – the amount of water currently in the soil – remains very high. This means the ground can't absorb as much snowmelt and rainfall.
: Streamflow is how much water is already flowing through the rivers at this time. Streamflow is running high, so it won’t take as much new water coming into the rivers to cause flooding.
Fortunately, because we've avoided really cold air this season, there isn't as much frost in the ground. Deeply frozen ground causes snowmelt and rain to run straight into the streams and rivers without absorbing much.
For tributary rivers (all except the Mississippi), how significant the flooding gets this spring will depend a lot on rainfall.
This outlook for spring flooding, and doesn’t necessarily mean anything about the risk of summertime flooding. While spring flooding can make it easier for flooding to happen in the summer, that is not always what happens.
Below are the flood chances for the river forecast locations for our local basins, compared to the historical average. It compares the odds for reaching minor, moderate, and major flood stage.
Lansing:
Minor – 84% (average: 10%)
Moderate – 49% (average: 8%)
Major – 36% (average: Less than 5%)
McGregor:
Minor – Greater than 95% (average: 52%)
Moderate – Greater than 95% (average: 28%)
Major – 82% (average: 9%)
Guttenberg:
Minor – Greater than 95% (average: 46%)
Moderate – 90% (average: 14%)
Major – 52% (average: 5%)
Dubuque:
Minor – Greater than 95% (average: 52%)
Moderate – Greater than 95% (average: 44%)
Major – 90% (average: 13%)
Bellevue:
Minor – Greater than 95% (average: 34%)
Moderate – Greater than 95% (average: 26%)
Major – 85% (average: 11%)
Charles City:
Minor – 31% (average: 20%)
Moderate – 18% (average: 10%)
Major – 7% (average: 6%)
Janesville:
Minor – 8% (average: 9%)
Moderate – Less than 5% (average: Less than 5%)
Major – Less than 5% (average: Less than 5%)
Cedar Falls:
Minor – 72% (average: 44%)
Moderate – 25% (average: 21%)
Major: 9% (average: 10%)
Waterloo:
Minor – 38% (average: 32%)
Moderate – 5% (average: 6%)
Major – Less than 5% (average: Less than 5%)
Vinton:
Minor – 22% (average: 20%)
Moderate – 6% (average: 7%)
Major – 5% (average: Less than 5%)
Palo:
Minor – 23% (average: 24%)
Moderate – 6% (average: 7%)
Major – Less than 5% (average: Less than 5%)
Cedar Rapids:
Minor – 28% (average: 28%)
Moderate – 21% (average: 16%)
Major – 9% (average: 8%)
Cedar Bluff:
Minor – 28% (average: 31%)
Moderate – 9% (average: Less than 5%)
Major – Less than 5% (average: Less than 5%)
Conesville:
Minor – 77% (average: 55%)
Moderate – 23% (average: 30%)
Major – 9% (average: 8%)
Marshalltown:
Minor – 8% (average: 9%)
Moderate – Less than 5% (average: Less than 5%)
Major – Less than 5% (average: Less than 5%)
Tama:
Minor – 22% (average: 22%)
Moderate – 16% (average: 14%)
Major – Less than 5% (average: Less than 5%)
Marengo:
Minor – 78% (average: 69%)
Moderate – 52% (average: 48%)
Major – 5% (average: 6%)
Iowa City:
Minor – Less than 5% (average: 6%)
Moderate – Less than 5% (average: Less than 5%)
Major – Less than 5% (average: Less than 5%)
Lone Tree:
Minor – 10% (average: 16%)
Moderate – Less than 5% (average: 7%)
Major – Less than 5% (average: Less than 5%)
Columbus Junction:
Minor – 16% (average: 14%)
Moderate – 8% (average: 5%)
Major – Less than 5% (average: Less than 5%)
Independence:
Minor – 14% (average: 8%)
Moderate – 8% (average: 7%)
Major – 6% (average: Less than 5%)
Anamosa:
Minor – 27% (average: 24%)
Moderate – 13% (average: 12%)
Major – Less than 5% (average: Less than 5%)
Kalona:
Minor – 52% (average: 50%)
Moderate – 34% (average: 33%)
Major – 9% (average: 15%)
Sigourney:
Minor – 55% (average: 56%)
Moderate – 35% (average: 42%)
Major – 6% (average: 11%)
Oskaloosa:
Minor – Less than 5% (average: Less than 5%)
Moderate – Less than 5% (average: Less than 5%)
Major – Less than 5% (average: Less than 5%)
Manchester:
Minor – 19% (average: 21%)
Moderate – 13% (average: 14%)
Major – 8% (average: 6%)
Maquoketa:
Minor – 16% (average: 14%)
Moderate – 6% (average: 10%)
Major – Less than 5% (average: 5%)
Elkader:
Minor – 82% (average: 47%)
Moderate – 42% (average: 23%)
Major – 17% (average: Less than 5%)
Garber:
Minor – 54% (average: 35%)
Moderate – 28% (average: 20%)
Major – 20% (average: 9%)
Decorah:
Minor – Less than 5% (average: Less than 5%)
Moderate – Less than 5% (average: Less than 5%)
Major – Less than 5% (average: Less than 5%)
Dorchester:
Minor – 37% (average: 20%)
Moderate – 12% (average: 6%)
Major – 11% (average: Less than 5%)
