In June the winter sets in for real. In the south, there is precipitation nearly everyday, but this comes as rain in the valleys and storms with zero visibility in the alpine. It's not the place to be. July and August are great for skiing in the more northern areas. Portillo and Las Leñas are busy and will get their biggest storms of the year. I focus my attention on the mountains around the Río Maule – about three-hours south of Santiago.
Over the past several years, the storms seem to be tracking a little farther south. Precipitation in South America is directly correlated with currents and temperature in the Pacific. It's been awhile since the sub-surface ocean temperatures were below average, which is what is required for the more northern areas in get pounded. (So the next time an El Niño period is called for, book your tickets to Chile!) For this reason, I am investing more time to the bigger mountains south of Santiago. It seems to snow more there.
Come September it's time to move farther south. For about five or six weeks of September and October, the skiing on the volcanoes is primetime. From Lonquimay to Osorno there is so much to explore. This is the time of year when the seasonal snowfall is the deepest, the access is the best and the weather stabilizes with more days of high pressure.
October is pretty late in the season. Spring has come to the areas in the north. The very high peaks – those above 4000-meters – can be excellent this time of year. Around the volcanoes the snowline has moved up and the approaches become long and the ski descents short. It's possible to head south again and explore Patagonia. This is pretty wild, rugged territory and there's plenty of skiing adventure to be had.
By November the season is pretty much cooked. Unless of course you want to cross to Antarctica. Hmmm...
The best time of year to ski in Chile depends on what you'd like to do and where you'd like to ski. As a general rule you can think that skiing in the north gets good sometime in July and as the season goes on, it is better to travel south until you hit the end of the southern cone in November.