I see that you said Yes, a pack author has the ability to configure DS behavior using external JSON config files, including turning on weather for a dimension. I just want to know is there any documentation to shows me how to use external JSON to enable weather for a dimension?

Thanks :)

https://github.com/OreCruncher/DynamicSurroundings/wiki/How-do-I#how-do-i-turn-off-the-nether-weather-effects

Though the specific example applies to the Nether (dimension ID -1) you can make tweaks to the settings to get what you need.

Closing out the issue. If you have further questions just ask. :)