Mississippi River flood risk climbs even higher in final spring flood outlook

First Alert Storm Team Meteorologist Corey Thompson lays out the chances for flooding in eastern Iowa, according to the final spring flood outlook.
Published: Mar. 10, 2023 at 4:35 PM CST
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CEDAR RAPIDS, Iowa (KCRG) - The final of three spring snowmelt flood outlooks has been released by the National Weather Service, and it shows a continued increased risk for flooding along the Mississippi River.

The outlook, which is issued by the NWS offices that serve eastern Iowa, showed an increased risk of surpassing flood stage for all locations along the Mississippi River. The probability of flooding for the Mississippi’s tributaries, which are all of the other rivers in the KCRG-TV9 viewing area, showed some slight increases but still below seasonal normals in most cases.

Contributing factors to the projected flood risk

The factor cited by the NWS as the reason for higher probabilities for flooding along the Mississippi River was an additional increase in the snowpack upstream in the upper portion of the river basin. The parade of winter storm systems has continued through the region, increasing the amount of water locked in that snow and ready to melt into streams and rivers.

Nearly the entire state of Minnesota has at least 10 inches of snow on the ground, with the areas of at least 20 inches on the ground having increased as well. Large portions of northern Wisconsin also have at least 20 inches of snow on the ground, which will also melt into the Mississippi River basin.

All told, that means we still have broad areas of 4 to 10 inches or more of liquid water equivalent in that snowpack, which will eventually melt and flow into the Mississippi. The critical factor for the severity of spring flooding for communities along will be how quickly it all melts. A rapid snowmelt, especially paired with additional rainfall on top of it, would lead to significant rises. But, a slower melt could limit the extent of flooding experienced.

Plenty of water waits in the snowpack in the upper Mississippi River basin to cause flooding...
Plenty of water waits in the snowpack in the upper Mississippi River basin to cause flooding downstream during the spring, depending on the speed of its melting.(KCRG / Data via NOHRSC)

For the Mississippi’s tributaries, though, the snowpack in the local area still remains below normal. In some cases, we’ve already seen some melting of that in the last two weeks, which has led to rises on area rivers. Combined with continued above normal precipitation over the recent weeks, this has reduced the capacity for area rivers to handle more water compared to the previous outlooks this spring.

As a single example, the Cedar River at Cedar Rapids is currently slowly falling after reaching its highest crest since late June 2020; however, it still crested safely below minor flood stage. This illustrates just how dry it’s been for a long time, though drought conditions have improved significantly in recent months in eastern Iowa. The river’s response to these conditions may indicate that it would be more likely to increase in the future, given the right conditions, rather than just having any rainfall soak into dry soil. The NWS noted this in their outlook, too, indicating that soil moisture levels were now near to slightly above normal.

How did things change between the two outlooks?

In many cases, the risk of flooding increased a bit again in the tributary rivers in eastern Iowa, but by a modest amount that kept overall probabilities below historical averages. One notable exception was the Cedar River basin, which saw probabilities decrease.

For a select group of tributaries:

  • Cedar River at Cedar Rapids: 12% chance of minor flooding in the third outlook, compared to a 21% chance in the second outlook, 18% in the first outlook, and a long-term average chance of 26%.
  • Iowa River at Marengo: 75% chance of minor flooding in the third outlook, compared to a 64% chance in the second outlook, 57% in the first outlook, and a long-term average chance of 68%.
  • Maquoketa River at Manchester: 18% chance of minor flooding in the third outlook, compared to a 18% chance of minor flooding in the second outlook, 15% in the first outlook, and a long-term average chance of 22%.
  • Wapsipinicon River at Anamosa: 24% chance of minor flooding in the third outlook, compared to a 20% chance of minor flooding in the second outlook, 16% chance in the first outlook, and a long-term average chance of 27%.

These changes were dwarfed by the continued increase in flood risk along the Mississippi River, though the risk of minor flooding was already maxed out in most cases:

  • Mississippi River at Dubuque: Greater than 95% chance of minor flooding in the third outlook, compared to a greater than 95% chance of minor flooding in the second outlook, 69% in the first outlook, and a long-term average chance of 53%.
  • Mississippi River at Rock Island: Greater than 95% chance of minor flooding in the third outlook, compared to a greater than 95% chance of minor flooding in the second outlook, 73% in the first outlook, and a long-term average chance of 61%.
  • Mississippi River at Muscatine: Greater than 95% chance of minor flooding in the third outlook, compared to a greater than 95% chance of minor flooding in the second outlook, 75% in the first outlook, and a long-term average chance of 62%.

Instead, it was the risk of major flooding at those same communities along the Mississippi that showed a more notable change:

  • Mississippi River at Dubuque: 69% chance of major flooding in the third outlook, compared to a 55% chance of major flooding in the second outlook, 26% in the first outlook, and a long-term average chance of 15%.
  • Mississippi River at Rock Island: 82% chance of major flooding in the third outlook, compared to a 69% chance of major flooding in the second outlook, 33% in the first outlook, and a long-term average chance of 25%.
  • Mississippi River at Muscatine: 81% chance of major flooding in the third outlook, compared to a 67% chance of major flooding in the second outlook, 33% in the first outlook, and a long-term average chance of 24%.

Just like low probability things can sometimes occur, high probability things can sometimes not occur. While major flooding is now likely on the Mississippi, Dubuque has almost a 1-in-3 chance to fall short of that level.

As always, we’ll be watching the future conditions to see how things change in the coming months. And count on the First Alert Storm Team to keep you updated on flood conditions for all of eastern Iowa, if they develop.