Girdwood has two equally good seasons, divided by a long shoulder.
Winter (mid-November to mid-April). Alyeska's ski season runs all winter. December is dark — civil twilight only lasts a few hours — but the night skiing under the lift lights is part of the appeal, and the chances of the aurora are high. Late February and March bring longer days and the best snow conditions on the upper mountain. April closes the resort with long warm afternoons.
Summer (mid-June to mid-September). The valley flips to hiking, biking and tramway tourism. July is the warmest month, with high temperatures around 18°C, very long daylight, and a steady risk of rain — Girdwood is the wettest town in the Anchorage municipality. Bring waterproofs. The bore tide on Turnagain Arm peaks around the new and full moons; check the schedule.
May and October are the shoulders: ski season finished, hiking trails still snow-bound at altitude, mosquitoes either not yet out or already gone. Many businesses run reduced hours.