The Fox River suddenly rose a foot in a half hour at Dayton late last night. That got the LaSalle County Emergency Management Agency’s attention. It sent a crew to watch for ice jams and flooding. The water was within a foot of flood level, but stayed below it and started dropping. The ice jam danger could be around for a few days.
As of this morning, there is no forecast for the Fox River. The National Weather Service issues river level forecasts there only when flooding is expected. The river rose slowly–about three feet over a 12-hour period–yesterday until the sudden quick rise last night from 11:15pm to 11:45pm. That’s how the river behaves when pieces of ice clog into narrow passages and block water flow. When ice lets go, the water level behind them can just as suddenly drop.
Correction: An earlier version of this story said the sudden rise happened in a quarter hour. The river went from 10.41 to 11.44 in a half hour.