Showers move through Chamonix on Saturday, with around 5 mm forecast for the valley. Sunday stays dry under cloud and reaches 13 °C in the afternoon. Pick Sunday. Higher up in Zermatt, at 1,600 metres, nights drop to around 2 °C while days climb past 11 °C. Start in a warm layer and expect to stow it by lunch. Friday began in fog in both valleys, so allow time for it to lift before you rely on the views.