A 13-degree swing in the Alps

Zermatt sat at 6°C at half past six this morning and climbs to 19°C by afternoon. Chamonix runs warmer, 11°C to 20°C. Both valleys stay dry through Monday. A 13-degree swing means the layer you start in is not the layer you walk in, and a merino base with a windproof shell covers both ends without a midlayer you carry unused.