Although Eastern Iowa is sitting under a layer of snow ranging from 8 to 20 inches — well above normal — that doesn’t necessarily translate to flood risks.
The risk of flooding on the Cedar and Iowa rivers this spring is at or below normal, according to the National Weather Service’s first prediction of the season.
The Cedar River at Cedar Rapids has a 5 percent likelihood of reaching major flood stage of 16 feet this spring, compared with the 7 percent historical average, the service reported Thursday. The risks of the river reaching minor or moderate flood stages also are below normal.
The Iowa River at Iowa City historically has a less than 5 percent chance of reaching its major flood stage of 26 feet, and that’s the predicted risk for this spring so far. The likelihood of minor flooding in Iowa City this spring is on par with historical risks.
Although there’s still a lot of winter to go down — remember the groundhog? — weather service meteorologists say lighter snowfall north eases flood risks here.
“Looking to the north across northern Iowa, Minnesota, and the northern half of Wisconsin, which includes areas that feed the Des Moines, Cedar, Iowa, Wapsipinicon and Mississippi Rivers, the majority of the region is observing below-normal snow depths and liquid water content in the snowpack,” the service said.
“For example, sites from northern Iowa into central Wisconsin including Mason City, Iowa, to La Crosse, Wis., are reporting snow totals anywhere from 5 to 10 inches below normal.”
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Also working in our favor to avoid flooding are dry soil conditions in much of the Upper Mississippi River watershed and a shallow frost depth. That last point might sound surprising with below-zero temperatures predicted through Sunday, but the relatively warm (for winter) temperatures in December and January kept the ground from freezing, the service reported. Then the heavy snowfall acted as a blanket, preventing deep frost development.
Below-normal temperatures in February so far will cause ice to thicken on Iowa rivers, raising the potential for ice jams when the rivers thaw, the service reported. An ice jam happens when chunks of ice carried in a stream’s current pile up at an obstruction and can cause flash flooding immediately upstream.
Thursday’s forecast was the first of the spring season. The service plans to issue updated flood forecasts Feb. 25 and March 11.
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