I would love to do the Olvidado / Invierno as never done those tracks, however unsure about albergues along that route at this time, and also wonder if it might be extremelty hot? Are there any online guide books for them?
If you can get on Facebook, take a look at this post. The author has laid out all his accommodations for an upcoming Olvidado. It is in Spanish, but the link to google brings you to his map with 22 accommodations indicated. This looks like a great resource, but be warned, the albergues are closed, so prices are higher than albergues.
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For the Invierno, as Kinky says, take a look at the
forum Invierno guide. The Invierno facebook page,
https://www.facebook.com/manuelangel.raimundezblanco, doesn’t have as much information, but apparently the albergue in Villavieja, 16 km outside Ponferrada, is open. There are fewer albergues on the Invierno than the Olvidado, though.
As far as the decision between Norte and Olvidado/Invierno, I have read that there have been difficulties finding lodging on the Norte. This problem is only going to be intensified throughout August, which is prime vacation time. If the albergues are closed, pilgrims have to take private accommodations, but the Norte is typically awash with tourists during summer, so that makes prices high and availability low. That makes me think private accommodations will be more plentiful and cheaper on the Olvidado/Invierno, which probably doesn’t see the rush of tourists that the Norte towns do.
I don’t know about temperatures, but since so much of the Olvidado is in higher elevations, I would guess it’s a bit cooler than lower routes. But that’s a totally unscientific guess.
Good luck with this, let us know what happens! Buen camino, Laurie