High pressure is sitting over Chamonix and Zermatt: no precipitation forecast through Sunday, and the valley climbs from 10 to 21 degrees by Saturday. Up at 2,500 metres it is a different story, 4.6 degrees this morning and near freezing at dawn on Saturday. That is a 17-degree gap between trailhead and ridge. Pack for both. A merino base layer and a windproof shell cover it without a midlayer you will carry unused.
Merino base layers ↗