The most popular times to visit Manali are May to June and September to October. May and June are warm and the Rohtang Pass road typically opens in late May, drawing large crowds of Indian tourists. The monsoon arrives in late June and runs through August — it rains heavily, roads can be blocked by landslides, and the Rohtang Pass may close temporarily. September and October are arguably the best months: the crowds thin after the school holidays, the sky clears, and the views are at their sharpest.
November to April is winter in Manali. The town remains open but tourist infrastructure is reduced. Snow arrives in December and the town is cold. Skiing is possible at Solang Valley from January to March, drawing a different winter crowd. If you are heading to Leh, the road is impassable from October to May (though the Atal Tunnel now keeps the Lahaul side accessible year-round). The Rohtang Pass road closes for the winter around November.