Summer is the most popular time to visit Michigan—people flock here for the beaches, inland lakes, and major events like the National Cherry Festival. July is typically the warmest month. In northern Michigan, it’s also the buggiest. Time a camping trip in mid-June or after mid-August, when the mosquitoes and black flies are less bothersome.
Autumn may be the best time to visit. Days are cool, night skies are clear, bugs are gone, and fall colors are outstanding. For peak color, the second week of September in the U.P. [1] and the second week of October for the Lower Peninsula are the best times.
Winter usually descends in December in the U.P., in January in the L.P., and can stick around through March. For snow sports, February is your safest bet to ensure good cover.
Spring emerges in southern Michigan in early May, working its way northward. With moderate temperatures and blossoming trees, spring is ideal for foliage lovers.
Links:
[1] http://www.moon.com/destinations/michigan/michigan-s-upper-peninsula