Seasons and the daily weather affect your town drastically. Seasons directly affect which furniture and clothing are trending during a particular season. Also, creatures like Bugs and Fishes only appear during a specific season throughout the year, and depends on the current weather if they will show up or not.
Winter season covers the town with snow and produces snowballs on the ground. This happens from mid-December up until late-February. You can create your own snowman by rolling together a big and small snowball. Further rolling it through the snow makes it larger, while rolling it on dirtground will reduce it's size. Talk to your snowman once he has been fully created, and if he is pleased at his own appearance he will give you a gift in return which you will receive via mail later. Only one snowman per day can be made and snowballs respawn at 6AM in the morning daily. Going in and out of buildings is one way to 'reset' the snowballs and make them respawn everytime you go back outside. A snowman will stay in the town for 3 to 4 days.
Summer heat gives your player a burnt-tan if you wander too much outside. This tan slowly disappears if you go inside buildings or use an umbrella when heading outside.