Settled Alps: warm by noon, freezing at dawn

High pressure has settled over the western Alps: three dry days from Chamonix to Zermatt, clear skies, valley highs near 25 degrees. But clear nights bleed the heat straight back out. Zermatt drops to 10 degrees in the valley, and above 2,500 metres you will set off below freezing. That is the catch of a settled spell. Warm afternoon, brutal alpine start. A wind shell over a merino base covers both ends without the midlayer you carry unused by noon.