The Chamonix valley takes around 26 millimetres of rain today before the sky clears. Wednesday and Thursday then stay dry, with highs near 24 degrees. The window is the afternoon. Sit out the wet morning, head up once it breaks, and pack a proper waterproof shell over a packable emergency layer. One valley east, Zermatt stays dry throughout at a calm 24 degrees.
Waterproof jackets ↗