I too used to avoid tracking in snow for the various reasons listed above (re sight tracking), however, that said, as Vinnie has pointed out, that would eliminate many other tracking situations too.
So last winter I decided to give it a go for pickle's sake, keeping in mind that Jax has a strong tracking foundation and she does well with tracking pretty consistently. She is able to complete an FH track done very well, just to give an idea of where she is at in her tracking.
After a winter of some semi-regular snow tracking, I didn't notice a decline in her tracking ability, committment to the track, or reduced scenting on the track when we resumed Spring/Summer tracking (we track in mud, on concrete, vegetation). While this is only one example for one dog/handler experience, I will be doing some winter tracking with her again this year. I do avoid the very cold dry days because I believe this is highly irritating to the inner mucosa of the nose.
With a dog or pup who does not yet have a good solid foundation in tracking, I would personally probably wait, but then again, I might try that too. I think one error many people make is to always track in the most ideal conditions and failing to introduce more variety into the tracking training earlier on and this often shows up later and poses some challenges for the dog to "transition" so to speak (I'm one of those people), so I'm changing things up and will do so in the future as well.
Last edited by Northern GSDs; 11-09-2011 at 08:53 PM.