Back when my family in Wisconsin were still living, I tried to visit about once per year. I usually tried to time it for mid September. It was beautiful then, the fall foliage was just getting started, the squirrels were busy hiding their winter stores, the mosquitoes were nearly done for the year. Along with early June, it's the best time of the year there.
Unfortunately, my mother was inconsiderate enough to pass in February.
If I never see snow and ice again it'll be too soon.