High Alps: settled mornings, stormy afternoons

Warm, calm mornings this week give way to building afternoons in the high Alps. Chamonix reaches 28 degrees today, then 18 millimetres of rain arrive on Thursday; Zermatt holds clear until Friday. That is the textbook August rhythm: storms gather fast over the massifs from around two o'clock, and above the tree line there is nowhere to shelter. Be over your highest pass by early afternoon. Start early.