Weather in this region of our world is extremely unpredictable. It is very important that travelers come well prepared for all weather conditions regardless of when you choose to travel. It is not rare to experience rain, wind, sunshine and even snow in a single day, even if traveling during the summer months.
The best time to visit Patagonia is October through March which is essentially the spring and summer months in Argentina. From October to April plan, Patagonia is good to visit for trekking, mountain biking, fly fishing, kayaking, rafting, hunting and golfing. From June to October, Patagonia is good for skiing. Prime time is in January.
Here you can find a forecast for the principal Patagonic Spots by Wind Guru:
http://www.windguru.cz/int/distr_iframe.php?u=478045&s=302954&c=a72a775b06
http://www.windguru.cz/int/distr_iframe.php?u=478045&s=325419&c=9a4f385d5e