[2020] Is theres seasons?

No seasons. You can have snow maps with Snowfall, that always has snow and gets snowfall from time to time. Or you can use some map themes that have a texture replaced with snow. It won't snow with those map themes, but if you want snow covered mountain tops, that can do it.

Here's a few examples of map themes with snow textures:

https://steamcommunity.com/sharedfiles/filedetails/?id=709145204&searchtext=snow

https://steamcommunity.com/sharedfiles/filedetails/?id=684085294&searchtext=snow

https://steamcommunity.com/sharedfiles/filedetails/?id=1774582619&searchtext=snow

https://steamcommunity.com/sharedfiles/filedetails/?id=633047095&searchtext=snow

https://steamcommunity.com/sharedfiles/filedetails/?id=1216255266&searchtext=snow