I think I understand the concept. Extrapolating the example of Rainy and Sunny days, how would you model this over a year, where there is seasonal variation? In

I think I understand the concept. Extrapolating the example of Rainy and Sunny days, how would you model this over a year, where there is seasonal variation? In winter for instance, the rainy days would more likely to continue than sunny days. And what are the recommended methods for creating models from existing data?