I was fortunate enough to ski AltaSnowbird for 10 days from Dec 20 - 30. We visit annually during Christmas/New Years week but this year was the best that I've personally experienced in 15 years of visiting. During those 10 days, it snowed 6 feet!! It was incredible for advanced to expert skiiers. The only downside was that the avalanche control guys could not keep up with the snow for a couple days. As a result, Snowbird was completely shut down one day so we want skiing at Alta that day instead. Road to Provo/Tiger Tail/Bookends never opened during my entire stay, I think because they just couldn't complete the avy control work in that area.
There was also a day with 80+ mph winds at the peak so the tram/Peruvian/Little Cloud lifts were shut down. It was also unseasonably cold for Utah during much of this time.
But the powder was great and the only limiting factor was your physical conditioning and skiing ability in order to consume the powder which was all over the place. It was a fantastic week that I'll remember for a long time.