How long indeed?
Obviously, there is no statutory definition or some sort of arbitrary of Wisconsin’s ski season.
Short answer, it depends. For the long answer read on.
The climate of Wisconsin like most other states is not one undifferentiated climate. Our climate varies by latitude and geography. Locations near Lakes Michigan and Superior have a more moderate climate and regions away from the Lakes have harsher climates. For example, our house is roughly a one-hour drive from Lake Michigan and we are on the border between growing zones 5 and 4.
Where I usually ski is solidly in zone 3 and the area known as “Big Snow Country” looks to be in region 4 (proximity to the Lake Superior Snow Making Machine).
The latest I have skied is probably mid-April. My brother and I left the cabin and people were out in front ice-fishing and when we returned there was open water where they were in the morning. The earliest I have skied is late November, but Ski Brule has been open as early as Halloween, and my father reports seeing Ski Brule open on Mother’s Day!
It is quite reasonable to believe Ski Brule will be open for skiing and ‘boarding from early November to Mid-April. How about the rest of Wisconsin and the UP? Usually no, especially down south in Wisconsin. Resorts such as Cascade, Nordic, Alpine Valley, Sunburst, Devil’s Head, etc do not have the same climate advantages. I will go up north in late March for skiing and when I leave home it seems more like fishing season than ski season (however, fishing does not open till the first Saturday of May) and up north it can still seem like full-on winter.
Big Snow Country resorts (i.e. Powderhorn, Blackjack, Indianhead, and Whitecap) usually close earlier than Ski Brule, but the reason is inadequate interest in skiing not due to inadequate snow. I have been to these resorts at the end of the season (Late March) and there is plenty of snow but they are closing anyway. I guess, with Bob Eucker on the radio a lot of people just forget about skiing.
Downstate, I would say the ski season ranges from early-mid December to early-mid March upstate and in the UP I would characterize it from mid-late November through late-March to mid-April.