Roof open or closed, here are the facts (From Football Zebras)
The commissioner and his designates make the decision if the retractable roof is to be open for the Super Bowl. This is the 7th Super Bowl with a retractable roof, and only once has it been open (Super Bowl XLIX, University of Phoenix Stadium, Glendale, Ariz.).
Under normal circumstances, a roof decision is made 90 minutes before kickoff, and the only time a roof position would change is to close an open roof when it starts raining. (This has never happened, as teams have kept their roof closed if there is a chance of precipitation.) For the Super Bowl, there have been special accommodations made, such as opening the roof for the halftime show.
The decision today is to leave the roof open for the player warmup period and close after the jet flyover after the National Anthem. The closing feature of the stadium will then be seen prior to kickoff. It is the first time for any game that we are aware of that players will warm up where the roof is not in its gametime position.