Autumn (late September to early December) gives the most reliably clear skies of the year. Post-monsoon air is washed clean, temperatures are moderate and mountain views are consistently sharp. It is also the busiest window.
Spring (March to May) is warmer, with rhododendron forests in full bloom below 3,500 m and the entire expedition season underway on the 8,000 m peaks. Afternoon haze is more common, so start early for views.
Winter treks are viable at lower altitude — Poon Hill, Mardi Himal, Langtang — with cold nights but empty trails and razor-sharp visibility. Monsoon (June to August) suits rain-shadow regions such as Upper Mustang and Dolpo.
Whichever window you pick, the gear list changes more with altitude than with season. Our per-trek recommendation already accounts for the season shown on each expedition page.