We start skiing in November around here, even late October some years… and ski until May!
December/January are the Powder months, expect fresh snow, shorter days, deeper snow. Most of the years snow falls in these months and conditions are often bottomless. Although I have had many clear sky days in the high alpine skiing wind pressed snow during these months too… we are in the mountains!
February/March are prime time, expect a good mix of sun and snow. Longer days and better chance of sunny skies means more likely to get into the alpine and ski some bigger peaks. It can also snow a lot so the best of both worlds!
April/May is prime spring conditions, expect long sunny days and high summits. Although we love skiing powder this is my favourite time to ski, I usually do more personal days in these months than any other. Stable weather and generally more stable snow allow for more interesting tours. Often we are climbing up in the sun in our base layers and skiing cold powder on the polar aspects.