It was the second seek of September in 1998 or 99 when I was bear hunting just west of Hurley and we got several inches of snow. Up in the Lake Superior snow belt region you can sometimes still go ice fishing Memorial Day weekend. I love being up in that area.
About the only time it doesn't snow in "extreme northern Wisconsin" is June, July and August. It's almost a seperate climate zone from the rest of the state.