Historically Zion only rarely gets snow. If by chance a big freak storm hits here, it also will hit in Vegas. That tells you how often we get snow. As to ice, again this is not a common thing. If we have a big cold snap, it is very likely. How often do those happen right now? Even with all the rain and such that caused destruction in the area last January, it didn't freeze in Zion. IF it should occur, it will happen in Feb. or March. January is the month we most often get the strange mid winter thaw. Two of the best times to be at Zion are in late March when the leaves and spring flowers are popping out. The shuttle that runs up through the main canyon starts mid March, which makes it a pain to do any large format photography. You have to ride the bus with all of your equipment, and are limited as to where they will stop. From there you will have to hike to where ever you want to go. The other time to be there is right now. The fall colors are spectacular. Which should be over in about a week to 10 days. After Nov. 1st the buses stop running so you are able to drive with your equipment to where you want to go. Those two times are also when the sun is low enough to have the magical light.
The two places within a 2 hour drive from Zion, are the ones that get the snow. Bryce Canyon and the North Rim of the Grand Canyon. Those usually do not have the big snow falls until after the first of the year.
BTW the road out to Grafton has been paved half way. Sad, the old dirt road was more quait and made for better pictures. Nothing like extreme ruts and washboard.