The season mechanic in Vikja the board game is pretty realistic and straightforward. You have the 4 seasons in a year, spring, summer, autumn and winter. A year is divided into 20 turns, so basically 5 turns on average per season. A season starts with 1 early turn, then 3 base turns and finally with 1 late turn in that exact order (see picture).
The 3 base turns are fixed and will not deviate from that particular season. The early and late turns however can vary, this means that there is a chance that the season can change on that turn to the next. A die is used to decide the outcome, in some cases an event card can change the season. In case of a die there is a 50% chance that the season will go the next, if it does not the current season will be kept for another turn until it does.
This mechanic allows a season to vary in length every year. You can have long winters, short summers, early spring, or an early winter for example. When you look at the schematic picture above you can see that winter can start on the early winter box and end on the late winter box to create a 'normal' season of 5 turns. However winter can also start on the late autumn box and last up to the early spring box continuing for a maximum of 7 turns. Such a long winter will make sure that the next spring will be shorter in length as the early spring box has been taken already.
The mechanic allows for some great combinations of season lengths within a year. For example a spring of 4, a summer of 5, an autumn of 4 and a winter of 7 turns, resulting in a long harsh winter. It adds a healthy variety and unpredictability to the game. Players have to deal with these changes all the time as different modifiers are in effect per season. Of course it's nice to have a long summer so plenty of bountiful harvests can be gathered and stored. On the other hand it could be devastating when players have colonized several locations and their first winter is very long, resulting in starvation, difficult roads and other effects.