The Four Seasons
Sims 2 Seasons will be localized to work in your region of the world. This article won't be, so let's start by pointing out that America's "Fall" is Europe's "Autumn". I'm willing to accommodate our majority audience here and will refer to the Season between Summer and Winter as Fall, but we all know what it means
Each neighborhood in your game can have its own climate which you can customize using the Season Chooser shown here, based on the 4 seasons of a year. This would allow you to make a region that is in a permanent Winter, always Summer or a combination similar to a California climate of Summer, Summer, Fall, Spring.
With Seasons comes a recognisable Calendar, displayed at the top right of the game control puck. In the example on the right you can see that we are just moving through Fall.
This is a weird climate, as we will soon be in Summer, then Winter, then Spring. This is actually as it was configured in my game, if you check out the earlier image of the Season Chooser. Whoops!
The calendar will progress at the rate of 6 Sims days per Season and rotates continuously, unless nature is thrown into disarray by the interference of a Sim using the Weathernaught 57X!