If 343 makes a new forge world, they should maje so that you are able to create your own terrain and add your own weather.
The map should be completely flat with no terrain, oly a flat landscape. This forge world would need its own gametype, and when you finish building the terrain, you would be able to go into normal forge to build your map.
The weather setting should be in the terrain builder as well, but it would turn on when you are playing custom games. Also for u would be able to add snow, water, etc, to the map when you are on terrain builder.
Right a post on what you think, and if you have any ideas.