The ski season runs from early June to early October each year. Snowfalls can start well before the ski season. The snow is usually at its peak depth and condition in August but often can be extremely good in July. By September days start to get a bit warmer and the snow can start to melt. There is still awesome “spring skiing” to be had and it can be great value as the rates are a lot cheaper.
The major resorts all now have extensive snow making facilities so that even without natural falls, the snow can be in great condition. You can ski from top to bottom at Thredbo more days per year now than you could in great snowfall years prior to snowmaking.