UPDATE: I wrote this post last night, but now as I sit in my hotel room in downtown Dallas, I see the snow accumulated on the road, and the temperature is below freezing. Schools are closed, Dallas-Fort Worth airport is closed (good thing the teams flew in yesterday) and Dallas is almost shut down. I don't see this having any effect on the Packers preparation or the game itself.
Mike McCarthy was interviewed before the Green Bay Packers traveled to Dallas. Via Packers.com, he said "the thing I always look for in weather is injury risk, and anytime the risk for injury increases, then it's time to go inside." Even after they arrived in Dallas he officially had not made a decision about practicing indoors.
According to NFL.com, he has since made it official. They'll practice at a local high school with indoor facilities, and not at SMU. The current weather report is calling for rain and wind on Tuesday, with freezing temperatures and wind on Wednesday that will turn the rain into ice. Obviously that makes for a serious injury risk.
In the end, I don't expect it will matter whether they practice inside or outside this week. Cowboys Stadium will have the roof closed, so they don't need to practice outdoors to get them ready for the game. Shouldn't they have scheduled practice inside anyway?
They won't begin practicing until Wednesday, after the temperature dips below freezing. Instead on Tuesday, they'll be at Cowboys Stadium for media day.