Best season to do Rupin - 15 May to 15 June & 15 September to Last October The trek starts from middle of May. It is not possible to do Rupin in the first weeks of May as the snow is too high. First time trekkers to high altitude trekking must target June rather than May to do Rupin. The best season in summer to do Rupin is in June. Monsoon hits the Rupin slope after first week of July.