Hourly Forecast Detailed. 1  0am:The Winnebago, IL forecast for Mar 14 is 21 degrees and Light snow. There is 87 percentage chance of rain and 14 mph winds from the North-Northeast. 2  3am:The Winnebago, IL forecast for Mar 14 is 19 degrees and Partly cloudy. There is 86 percentage chance of rain and 13 mph winds from the North.