Unless there aren't clouds around for 100s of km it'shard to imagine the roof being open. Their sound guys will need to do a soundcheck in a setting that will most closely resemble showtime. There's a huge difference between checking for an open dome vs. a closed dome.
SkyDome is a VERY disappointing choice by the promoters. Coldplay at the Amphitheatre would have been fantastic.
One can only hope that the promoter isn't planning on making it a fiull-stadium show (still no info on TM).
...hard to imagine ELBOW on the Skydome stage (very unfortunate for them)