Western Alps: the warm spell breaks this weekend

Late-summer heat is on its way out. Chamonix hits 29°C today, then a front rolls in on Friday with roughly 15mm of rain. By Saturday the valley tops out near 18°C, and at Zermatt's altitude the overnight low drops to about 7°C. The freezing level falls with it. Pack a warm layer even for a fair-weather summit, and check the forecast again before committing to a high route.