Alishan is most famous for its autumn cloud sea (October to December) and spring cherry blossoms (late March to mid-April). Both seasons bring huge crowds — plan and book well ahead.
The winter months (December to February) are cold at 2,200 metres, occasionally frosty, and sometimes see snow. The cloud sea can be spectacular in winter. Summer (June to September) is Taiwan's typhoon season and can bring heavy rain that closes the forest railway; this is the least reliable time to visit.
The sweet spots are October–November (cloud sea, cool temperatures, post-typhoon clarity) and early March (before blossom crowds, quieter, crisp air). Weekdays are significantly less crowded than weekends regardless of season.