The "weather-question" is always a difficult one to answer since the camino goes over a long stretch and at different altitudes. Have a look here for some ideas: viewtopic.php?t=515
... the weather in Galicia has a tendency to change fro minute to minute, so one day could have a mix of all types of weather. The last few weeks in Galicia (today is February 15th) has been sunny and we have had temperatures of about 15c during the day. Minimums over night of about 2-3c.