The Annapurna region has two main trekking seasons and two seasons to avoid.
October to November is peak season — the post-monsoon window when skies are clearest, views are sharpest, and the rhododendrons on the lower slopes have fresh washed colours. Trails are busy and teahouses sometimes full; book ahead at popular stops like Manang and Ghorepani.
March to May is the second season, with rhododendrons in bloom from 1,500m to 3,000m and temperatures warming on the lower sections. Spring haze can reduce mountain visibility, but the colour of the forests compensates.
December to February is cold but possible. Snow can close Thorong La intermittently, and the high-altitude sections are frigid. The trails are quiet and teahouses cheaper, but you need proper winter gear above 4,000m.
June to September is monsoon. The southern circuit is inadvisable — leeches, cloud, and slippery trails make for miserable walking. The northern section (Manang, Mustang) is in a rain shadow and remains walkable; some trekkers deliberately do the upper circuit in monsoon for the empty trails and Tibetan character. Poon Hill and the Sanctuary are best avoided entirely in this season.