According to actor Liam Neeson's account, the temperatures were as low as -40°C in Smithers (British Columbia) where the film was shot. The snow storms/scenes were actual prevailing weather conditions and not a cinematic illusion produced with CGI trickery (interview: The Tonight Show with Jay Leno: Episode #20.70 (2012)). The cast wore thermals under their costumes for additional protection.
In his glowing review of this film, Roger Ebert stated that in his long career, this was the only time that he actually walked out of his next scheduled screening because it affected him so. "After The Grey (2011) was over, I watched the second film for 30 minutes and then got up and walked out of the theater. It was the first time I've ever walked out of a film because of the previous film. The way I was feeling in my gut, it just wouldn't have been fair to the next film."
This film was denounced by endangered-species protection organizations for its portrayal of wolves as a perpetual threat to humans. It was felt that the film reinforces the ancient cultural notion that humans should follow a kill-or-be-killed policy whenever encountering wolves.
The trivia item below may give away important plot points.
There is a brief scene after the end credits which shows the alpha wolf lying on his side breathing heavily and Ottway's head resting on the wolf's stomach. If you listen carefully you can also hear Ottway breathing as well. The scene remains ambiguous as to who is the victor.