We do sometimes get snow on the Trotternish ridge as early as mid November but it rarely stays very long.
Some heavier falls can occur in December but again doesn't tend to last more than a few days unless it's a particularly long cold spell and there might be some lying snow through to January.
Late December and into January and February the snow can heavier and stay longer (weeks) on the tops.
Snow has fallen on the ridge at the end of April (2015), so it can be somewhat unpredictable.
The main thing you can almost bank on is wind, rain and temperatures in single figures on the tops but you never can tell when the odd high turns up and it is clear, still and very cold.
If you want to put up a post nearer the time you plan to come up to Skye I can look out of the window and tell you what the conditions are like on the ridge.
Here's a picture of the Storr (from 7 miles away and a big crop of the full frame) taken 31st January this year.