The recent cold snap allowed ice to quickly form on local rivers. But the warm up has caused the ice to break apart and travel down river. Unfortunately, ice jams have been developing along the Rock and Pecatonica Rivers causing flooding in a few communities. Ice jam flooding is different than heavy rain flooding. It's more localized and occurs with very little warning.
A Flood Advisory is in effect for the Pecatonica River at Shirland and for the Rock River at Dixon. An Areal Flood Warning has been issued for the Rock River near the Ogle/Lee County line near Grand Detour, IL. Ice spotters have reported ice jams with flooding occurring Thursday afternoon.
This picture is of the ice on the Rock River in Grand Detour. If you look closely at the tree line, you can see just how high the river has gone. The rainfall Thursday evening won't be anything like what we experienced on Monday, but the added rain won't help. Scattered showers will continue on and off through the weekend, but totals should remain light.
The river gauge in Bryon is quite interesting to look at. Notice how the river level rises Monday due to the heavy rain, but then quickly drops and then rises again. For a time the river did reach minor flood stage, with homes being reported flooded south of Byron. The rapid rise and fall of the river level (assuming it's not malfunctioning) is likely due to ice jamming. The ice jam causes the water to back up upstream and slow down. Once that jam breaks apart, the river water is flowing again - until another ice jam occurs. This is why ice jams occur with little warning and residents along the rivers need to keep a watchful eye on river levels.