A dry window in the Alps from Thursday

Today's showers clear overnight. Thursday and Friday come up dry in both Chamonix and Zermatt, with valley highs of 18 and 17 degrees. The mornings stay cold: 10 degrees in Chamonix, under 8 in Zermatt, and colder again as soon as you gain height. That gap between dawn and afternoon is the whole trick of September. Pack for both. A warm layer you can stow by nine, and reach for again on the descent, beats a midlayer you carry all day.