Check forecasts before departure and again that morning. Look at the update time, rain periods and warnings. A city forecast does not replace local information for mountains or other destinations.
For an outdoor-heavy day, identify an indoor alternative whose opening and booking rules you have checked. Assess travel and safety conditions before changing plans; rain does not guarantee last-minute museum entry.
Wear suitable walking shoes and keep your bag light. Agree with the guide how weather changes affect contact, timing and fees before the day begins.