I'm quite certain hard rain is possible. I'm not too savvy when it comes to making weather and it's been awhile since I've even touched Sky Maker so I'm just relying on (my very bad) memory here, but there's definitely a way to make the rain more frequent or have it 'rain harder'. Just like how there's the Light Rain option.
As for lightning. There are multiple object packs out there with lightning that strikes every so often, but if you want it to behave like weather cycles, I'm not too sure. I think it might be possible, I'll have to tinker around with the weather files to see if anything of the sort could happen.
I haven't seen many actual weather mods like this up for download though. If I can figure out how the weather works I might see what I can do.
EDIT: Apologies, posted before I noticed you wanted the thread locked.