Camino Ingles in January

You could try the Spanish AEMet site here for objective information. You will need to navigate to climate data then normal values to get to a map interface.

I walked the Camino Ingles in mid-January with a friend in warm daytime sunshine, cool (near freezing) nights and a total of about 20 minutes of light drizzle. Our main weather concern was sunburn! My friend had walked the same route at the same time in two previous years in near-constant rain and howling gales - a complete contrast. Whatever the historical averages might suggest you need to be prepared for some wild and wet weather and cold nights. The weather in Galicia in winter is very unpredictable.