The season is basically the same here in Chicagoland. I don't drive mine after the first salting of the roads in the winter, or until after a couple good rains in the Spring. But if the weather is nice in February I'll drive around. The semi-organized shows usually start in mid-April, but a lot of planners are a little cautious because people avoid the rain, so there is no point in planning something that doesn't have a good chance of good attendance.
And for those who are in Illinois, Wisconsin, Iowa, Minnesota, Missouri, Nebraska and Kansas, I maintain a google calendar of all the events I know about. You can access it by going to http:/www.calendar.google.com and then search "Heartland Region Car Shows and Cruise Nights" and you'll have access to it. It also has AACA, BCA and ROA events around the country.