Wisconsin winters are serious — Appleton averages well below freezing from December through February, and lake-effect snow from Lake Michigan can pile up fast. Unless you are coming specifically for winter outdoor activities, June through September is when the city is most pleasant, with warm days, active outdoor culture along the Fox River, and a full schedule of events.
The Fox Cities Marathon runs in September and draws big crowds. The Houdini Birthday Bash in late October celebrates the escape artist's October 24 birthday. Lawrence University's academic calendar means the city is livelier during the school year (September–May) than in summer, when the student population thins out.