I just have implemented weather system. We've got now 3 weather types: Clear, Mild Rain and Heavy Rain. Each of these has a different impact on the town's life. During a clear weather, villagers behave normally and sticks to his regular schedule. Mild weather is pretty much the same as the regular one, however, it also waters your fields, which allows you to save some time and spend it on the other way. Heavy rain, on the other hand, is so bad that everyone prefers to stay in rather than to go outside. Player happens to get tired more quickly during the bad weather as well!