Western Alps: a nine-degree swing in a day

High summer is loosening its grip on the western Alps. Chamonix touches 28 degrees this afternoon, then tomorrow's high falls to 19. That is a nine-degree drop overnight. Valley mornings already sit near 13 degrees, and it stays colder the higher you climb. A light windproof shell over a merino base covers both ends of the day, without the weight of a midlayer you would carry unused past noon.