There are 4 seasons in URW calendar, just like in the real world. They are spring, summer, autumn and winter. All seasons have a different effect on gameplay, such as temperature and plant growth.
Spring is dry, with early spring being reasonably cold. Ice starts to melt and plants begin to grow again, although this usually occurs in May. Before May, the weather is dry enough to dry food. It is more forgiving than winter, but is not as easy to live in as summer. Starting in spring gives players plenty of time to prepare for winter. (March, April and May)
Summer is the easiest season to live in, and so new players are advised to start in summer. It is warm, so there is no risk of frostbite, and crops grow readily, as do berries and mushrooms. There is still enough time to prepare for winter, but it is too humid to dry food, forcing players to preserve meat through smoking or salting instead. (June, July, August)
Autumn is similar to summer, but is slightly colder. Different varieties of mushrooms are available in winter such as the Tellervo's Gift mushroom, but autumn does not afford much time to prepare for winter. Crops are still harvestable throughout autumn. Again, it is not dry enough to preserve food by drying. (September, October, November)
-Drying food can be prepared in October (3.15)
The coldest and harshest of the four seasons, surviving winter takes preparation. Temperatures are regularly below freezing, thus making frostbite a very real possibility. Snow blankets the land, so skis are needed to move quickly. No plants will grow during winter. However, winter freezes water, allowing players to walk over ice (although holes need to be made in ice for fishing. The cold weather also preserves food, and it is dry enough for drying meat. (December, January, February)