Risk of flooding in the Illinois Valley this spring is low, so far

The Illinois Valley is in a drought and the Illinois River is low. So far, it doesn’t look like there’s a big risk of late-winter/early-spring flooding.

But that could turn on a dime.

Meteorologists with the National Weather Service for the Chicago and Quad Cities regions said Thursday the current spring flood threat is near-normal to below-normal. That’s mainly because of a dry start to winter and subsoil frost that isn’t deep.

But in the next breaths, the meteorologists said the 10-day outlook bears watching because it’s going to get colder and there could be snow. Old Man Winter could change the flood outlook abruptly.

“One system can change this drastically,” said Timothy Gunkel, a meteorologist and acting hydro program manager for NWS Quad Cities.

“We still have a solid month of winter left,” said Todd Kluber, a meteorologist in Romeoville.

Much of the Illinois Valley is in a moderate drought, according to the U.S. Drought Monitor. For farmers, that’s a situation that bears watching. David Isermann, president of the La Salle County Farm Bureau, said there are no moisture reserves in the soil though that situation could be erased when spring rains arrive.

The lingering drought has reduced the risk of flooding, however. As Kluber said, mild December temperatures didn’t result in much frost buildup which in turn kept moisture from penetrating the deep soil. There is room in the ground to absorb precipitation – once the soil thaws, that is – as opposed to swelling the rivers.

And while the ground is frozen, the frost is not deep. Gunkel reported temperatures of 1 to 2 degrees above normal, which in turn limited frost depth to 6 inches in Davenport, 7 inches in Romeoville and 9 inches in Coal City. Consider that the Milwaukee region has reported frost depths of 15 to 25 inches.

As a result, the Mississippi River has a 10% to 15% chance of reaching major flooding and the outlook on tributary rivers including the Illinois are similarly moderate.

“But all it takes is just a couple of big rainmakers or, if we build up heavy snow pack and have a rain event, that would definitely increase the risk of flooding,” Kluber said.