Alps: warm afternoons, cold starts, rain from the 25th

High summer is loosening its grip on the Alps. At 1,600 metres around Zermatt, mornings start near 8°C, while the valleys push past 24°C by mid-afternoon. That is a swing worth dressing for. A merino base layer under a light windproof handles both ends, without the bulk of a midlayer you carry unused all day. One thing to plan around: a front rolls in on the 25th, with 7 to 8 mm of rain forecast for Chamonix and Zermatt. Go early in the window.