Altaussee has two distinct seasons. May to October is the green season: hiking, lake-swimming (in July and August, briefly), boat trips, mountain biking. June is particularly beautiful — wildflowers on the meadows, long evenings, fewer visitors than the school-holiday peak in late July and August.
December to March is ski season, though the resort is modest by Austrian standards — the Loser plateau has a handful of easy and intermediate runs, and the village is more about quiet snowy walks and traditional events than serious skiing. The Glöcklerlauf on January 5th, a torchlit procession of masked figures meant to drive out winter, is a striking local tradition.
Shoulder months (April, November) are quiet, often cool and grey, and many hotels and restaurants close. Late September into mid-October — the so-called golden autumn, when the larch needles turn yellow — is one of the loveliest times of year.