Like if it’s rainy, guests get more unhappy, and rides break down easier. If it’s windy, tall rides shut down, and guests get unhappy (again). If there’s thunder, the park is much quieter. If it’s cloudy, there are no effects. If it’s sunny, guests get happy easier, but it’s much more busy. You can add shops like umbrella shops too, and you can add little shelters where guests stand under to shelter from rain or wind.