sopf,
It was just a practice, not a match so we weren't overly concerned with rules compliance, especially given the conditions.
That said, most shooters were following the regular IDPA concealment rules. Most started jacket open, just like in the summer. No one used a pocket to "holster" their handgun. No one started from low ready. One had the holster on the outside of the snow suit, but that could easily have been made legal with a jacket over that.
Why would you want to carry in a flap holster for an IDPA event? The concealed handgun is protected from the elements and it's probably going to have less mechanical issues due to being warmer. You could shoot strictly by the rules in the winter and have zero problems complying with them.
The only malfunction issues we had were glove-related. IE: FTE due to glove preventing the slide from moving rearward or "this damn glove is too big to fit in the trigger guard". Obviously, mittens don't work worth a ####.