I invoke the most important rule And use a SECOND fateweaver to change that roll HEHE
http://www.games-workshop.com/en-GB/age-of-sigmar-compendiums Hope this works for you.
I pretended I was a New Zealander for a bit. They'll be up for the US soon, tomorrow at the latest.
You can't use Fateweaver's ability to declare that the roll is a 13, because you can't roll 13. In the same manner you can't declare it's five...