As a workaround, until the [extrainfo] inf's are able to be easily changed at will, weather can be added to the two Mini Cities by simply selecting another set's (any of the landscapes work well) inf and renaming it to the mini city set you wish to use.
Be aware that doing this will limit your available shots as you will lose the skydome, but freecam of course will remain unaffected.
Furthermore, you can experiment with different colored fogs by renaming another sets for to the mini city set you wish to use. For example, the desert sets fog give a smog or dust color when used.
Good luck and have fun.