It is a climate typical of high mountains; more rain in winter with plenty of snow, and milder and dry during summer. Winds from the west (Pacific Ocean) prevail.
Besides, weather in Bariloche ranges from very humid at the Andes, to the West (this is the region where it rains the most countrywide), to arid and desert to the East, right where the meseta Patagonica (plateau) starts. Rain increases westbound.
Both fall and spring are fresh, with cold nights. Autumn is when the wind is calmer however it rains more whereas spring is windier and dryer.
To sum up, you must always be prepared for cold or chill weather, no matter which time of the year you come, you must bring a jacket!