A settled Alpine window, cold at dawn

High pressure sits over the western Alps for the next three days. In Zermatt the morning starts near 6°C at 1,600 metres, then Chamonix climbs past 23°C by afternoon. That is a 17-degree swing before lunch. No rain in the forecast. A merino base layer under a packable windproof handles the dawn chill without the bulk you would carry unused once the sun is up.