According to the fall foliage map at https://smokymountains.com/fall-foliage-map/ we should reach peak colors in Southern Wisconsin on October 12, so maybe the preceding weekend.
Colors are starting to change already so by the end of September and each weekend till the middle of October for sure, you should see some beautiful colors.
I was going to say the same thing as Brett. Funny enough. He's my husband.
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