Hey there.
I just tried to create a dimension with thunder.
If i understand the dimlets correct the thunder dimlet should be thunder only right?
This is my dimlet:
http://fs1.directupload.net/images/150720/ngnz45me.jpg
This is how my dimension looks:
http://fs2.directupload.net/images/150720/rdsvcajj.png

Seems like the thunder dimlet is not working. :(

Using the latest version of RFtools and forge 10.13.4.1481

Note that thunder only works if it is also raining. So you probably also want to add rain dimlet to it. That's not an rftools thing but a minecraft limitation.

Ah i thought
rain dimlet = rain only
thunder dimlet = rain + thunder
I added the rain dimlet and its working now. Thank you! :)
Maybe there is a way to automaticly add rain if the thunder dimlet is added?
I think this would be the most logic way. :/

Well the thunder dimlet on its own is still useful in case you want it to always thunder in case there also happens to be rain. So it really is a distinct thing.

Ah ok, that makes sense.
Anyways, problem is solved, thank you! :)