The best time to visit Gilgit is May to October. This is the dry season in the mountains: passes are open, the Karakoram Highway is at its most reliable, and the trekking routes above town are accessible. July brings the Shandur Polo Festival, the high-altitude polo tournament at 3,700 metres between Gilgit and Chitral, which attracts visitors from across Pakistan and is worth planning around if your schedule allows.
Summer (June–August) is hot in Gilgit town itself — the dry valley traps heat and temperatures can reach 35–40°C at midday. The mountains above are cooler and this is the busiest time for trekkers heading to Rakaposhi, Nanga Parbat base camp, or the high-altitude routes. Flights from Islamabad operate most frequently in summer, though cancellations due to mountain weather remain common.
September and October offer a useful compromise: the heat has eased, the main trekking routes are still open, and the fruit markets are full of the apricots, mulberries, and walnuts for which the northern valleys are famous. The light in autumn is cleaner and the crowds thinner than in July.
Winter (November–March) closes the passes. The Khunjerab Pass to China shuts, roads to Skardu and Chitral become unreliable, and the town contracts. Gilgit does not get heavy snowfall at its valley-floor elevation, but it is cold, grey, and quiet. Air travel in and out becomes even more erratic. Unless you have a specific reason to visit in winter, there is little to recommend it.