Hi Rambojoz,
This issue is one the team are aware of and appears to be related to the weather effects doubling up, and as Damselx1 mentioned, it can also get stuck on one type of weather.
Clearing the cache as Damselx1 described above is the best method for resetting the weather effects. While I know it may not be ideal, it is the most effective workaround while the team are working on finding a solution to this issue.
Could you please tell me what type of game you are playing (single, multiplayer, splitscreen), how old the save is and if you notice if any particular areas trigger the effect?
Thank you,
Clare