Just in from the Chicago National Weather Service is how rare this weekend's daily temperature change was for Northern Illinois.
High Saturday: 41°
High Sunday: 75°
High Monday: 42°
Over a 30 degree temperature change occurred from Saturday to Sunday, and then Sunday to Monday. This has only occurred one other time in Rockford, February 2nd-4th, 1970.
According to the National Weather Service there have been some other close instances back in January, 1996 and April, 1978.