Despite custom dimensions having weather independent of the Overworld, it can't be controlled by any commands, even when using /execute. This should affect any datapack with a dimension that uses the "Overworld" settings for sky and fog.
Steps to reproduce:
1. In the Overworld, run /execute in minecraft:overworld run weather rain
The weather will switch to rain, as expected.
2. Teleport to your custom dimension, then run /execute in [your dimension] run weather rain
The weather will not change.
Strangely enough, just because you can't control the weather in a custom dimension does not mean it doesn't have any. If you sit long enough in a custom dimension, rain and thunder can appear like they may in the Overworld, you just can't control it.
Thank you for your report!
However, we are already tracking this issue, and this report is a Duplicate of MC-186626, which is a report that has not been resolved yet.
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