Flooding unlikely from expected warm-up, but experts see potential issues for spring

While most of us crave quick relief from the snow and cold that has gripped the area in recent weeks, weather and waterway experts say a slow and steady warm-up is preferable because harsh winters sometimes contribute to spring floods that could affect communities along the Des Plaines and Fox rivers.

The National Weather Service, in its recent flood outlook, predicted an above-average chance of spring flooding for the Des Plaines and Fox rivers. However, the warm-up expected over the next few days - with temperatures possibly reaching above 40 - is unlikely to cause a thaw significant enough to result in flooding any time soon, officials say.

“We're always on high alert in regards to flooding because we sit right along” the DuPage River, said Naperville spokesperson Linda LaColoche. “It's not like it's going to warm up so quickly that it's going to cause a rush of water. It's going to be a gradual melt.”

Brad Burke, Lincolnshire's village manager, says the Des Plaines River is about 5 feet below the stage where mitigation efforts would be necessary, putting the Lake County municipality “in a fairly decent position.”

“A snow melt locally is not going to drive the water levels up to create localized flooding unless one of our inlets becomes plugged or iced over,” Burke said, adding that village crews are monitoring water levels.

With the Des Plaines River currently iced over, flooding isn't a primary concern right now, said Wally Dittrich, Lincolnshire assistant public works director and village engineer. Flooding, however, could be a factor in the spring if temperatures rise, a downpour occurs and “everything melts at once,” Dittrich said.

The best thing for municipalities located near rivers “is a gradual melt off without a lot of precipitation,” Dittrich said.

In its spring flood outlook released Feb. 11, National Weather Service experts rate the chance of spring flooding as above average. The agency will release additional updates Feb. 25 and March 11.

The updates examine “a set of conditions to try to get a feel of whether or not our flood risk is above average, near average or below average,” said Scott Lincoln, senior service hydrologist with the weather service's Chicago office.

Snow cover, soil moisture and recent river levels can indicate the relative risk of spring flooding, said Lincoln. But none of those factors is a perfect predictor. Any weather system that produces heavy rainfall could also cause flooding, he said. Spring outlooks cannot assess the risk of flooding due to heavy rainfall more than a week or so in advance.

“If the temperatures warm to a little bit above freezing, it allows the snow cover to melt slowly. The water would soak into the ground and flow toward rivers which would rise but which would not result in flooding necessarily,” Lincoln said.

Temperatures in the 50s or above, however, would melt the snow more quickly, which means moisture in the ground would rush to rivers.

A significant river rise could break up the “substantial ice cover” that has built up on several area rivers, Lincoln said. That ice could cause a jam, which might lead to flooding.

“We don't want it to melt all at once,” Lincoln said.

At this point, the moisture level in the soil is lower than last year, Lincoln said, but 2021 has brought a lot more snow.

“That's one of the factors that pushes us toward calling for an above-average risk of flooding,” he said.

“You're always concerned when there's a couple of feet of snow on the ground, which is the case now,” said Joe Keller, executive director of the Fox Waterway Agency.

To accommodate melting snow and ice, state officials may lower the water level of the upper Fox River and the Chain O' Lakes at the Stratton Lock and Dam in McHenry County, Keller said.

“They literally bring down the system a foot and a half” to accommodate melting snow and ice, he said.

Keller agrees “slow and steady wins the race” and a gradual warm-up is more desirable where snow cover is concerned. And looking forward, he is optimistic about the upcoming boating season on the Chain O' Lakes.

“Especially during the pandemic, folks have found a lot of peace and tranquility on our waterway,” he said. “We want to encourage that.”