To copy from another thread, there’s been some discussion about seasons already, specifically relating to timescales.
It seems as though the four seasons will be simulated (one week each), and I hope that seasonal demand is also included (seasonal flights, peaks and troughs of traffic etc).
That said, I’m not sure if climate can also be simulated. There are going to be regions in the game, and of course each region has a different climate that may change what the weather will be like in each season (for example, winter in Scandinavia will be cold and snowy, but winter in the Mediterranean would be warmer and probably wouldn’t see snow).