The standard advice is that Nepal has two trekking seasons, autumn and spring, and that June to September is written off to rain and leeches. On most routes that is correct. On three it is completely wrong.

Why the rain shadow exists

The monsoon arrives from the south and drops its moisture climbing the main Himalayan chain. North of that divide — geographically part of the Tibetan plateau — very little rain falls at all. Upper Mustang, Nar Phu and Upper Dolpo all sit behind the wall.

Upper Mustang

The best summer trek in Nepal. High desert of eroded ochre canyons, cliff-cut sky caves and the walled city of Lo Manthang at 3,840m, all dry while the rest of the country is under cloud. Expect clear mornings and relentless afternoon wind — most days start early for that reason. The Tiji Festival at Lo Manthang, usually held in May, is worth planning around; book six months ahead. See the itinerary.

Nar Phu Valley

Two Tibetan villages in a side canyon off the Annapurna Circuit, sealed to foreigners until 2003 and visited by only a few hundred trekkers a year. Monsoon brings clear mornings and dry trails here. It is a genuinely demanding trek — Kang La at 5,320m is a long, cold, exposed day — and a restricted area requiring a minimum of two trekkers and a licensed guide. See the itinerary.

Upper Dolpo

The most remote region in Nepal, and the only one where May to September is not just viable but the recommended season — the passes are clear of snow and the villages are occupied. Phoksundo Lake, Shey Gompa beneath the Crystal Mountain, and five passes above 5,000m across twenty-three days of full-service camping. Winter is not an option here: the passes close. See the itinerary.

A lower-cost alternative

If the USD 500 restricted permit is out of range, Lower Mustang sits in the same rain shadow and needs only ACAP and TIMS. Eight days, Kagbeni, Muktinath and Marpha.

What to expect getting there

The approach still crosses monsoon country. Roads to Besisahar and flights to Jomsom, Nepalgunj and Juphal are all more prone to delay in summer, so build in buffer days. Once you are past the divide, the weather changes completely.