At that time of the year, "better weather" for cycling you will get will be on the...
--Via De La Plata. Southern part.
-- Or, ride southern Portugal to Santiago. But you know the story as you head north....
-- Or, ride Granada to Seville. Won't get you to Santiago. But a option for nice weather riding.
-- Or, Majorca Ditto on nice weather riding.
-- Or, Augusta?
These may not get you to Santiago. But do that on another ride.
There is a bike route along the southern tip of Portugal. Not a Camino. But nice to ride that time of the year. You can find it on the web.
Visiting Cadiz that time of the year is nice. Then ride to Seville. Also nice. But Via Augusta from Cadiz to Seville is not the best as far as markings, route, etc. Read Via Augusta on this forum. From Seville you could then ride part of the Plata.
I grew up in Seville and Ferrol (Galicia) Visit northern Spain often. Now living in Seville. I know what the weather can be up there (where you may be riding)... winds...high winds, wet, cold, damp, and yes snow. And many places closed or shorten hours. Add shorten daylight hours for riding may make for not a nice ride.
Is it possible for you to come at a better time of the year to do a Camino? Possibly days off, schedule, work, family, etc prevent you from riding during a better time of the year??