Patagonia weather is difficult to predict, and even any Internet forecast service can be erroneous. It's important to know, especially for this region, the further out a forecast predicts the more it plays with pure chance. These forecasts will vary almost always between sunny, partly cloudy, drizzle and rain. Wind alone rarely is a factor especially compared to southern Patagonia.
Comparing the weather to other years. If you compare, for example, February of one year with a previous February, it can be similar or totally different. There is no recipe for how much time you will have on your scheduled vacation. It is part of the "Cochamo experience". The average temperature between December and March is between 14°C and 17°C. The average rainfall between December and March is between 110 and 140 mm.
Getting the forecast once in the valley. If you're staying at the Camping La Junta or Refugio Cochamó, you can get updated forecasts there posted on their information board.
The local way. While in the valley locals follow one general rule that helps forecast weather. Clouds moving in a somewhat north-to-south direction means rain is coming. While south-to-north or directly west-to-east winds or cloud movement means stable weather will hold.