On the question about local variations irrespective of weather, temperature or major latitude difference:
None of what I've found above gets to the question of whether it's realistic for air pressure to be different at a given altitude for two peaks close together on a global scale - say 10km or 200km apart, that kind of range. A plausible reason might be a prevailing wind, if the Puelche wind coming from the East of the Andes coming from 2000m high Argentina plains then blows across the Andes and blows down to the west side of the Andes, which drops more quickly to nearer sea level, could that effect of low pressure winds from the East drive down the pressure on the Western side of the Andes vs the East? It's logical, but I'm not convinced that it would make such a huge difference. The Andes are pretty wide you would think pressure differences would level out soon enough due to the inevitable movement of high pressure air into low pressure spaces that can easily be seen by opening a bottle or crisp packet closed at a different altitude. The air in this case equalizes very very fast.
Also, if what the guide says was true (and he was talking about mountains in the same region of the country), and if it was a big effect, you would think it would be more documented. THe fact that I'm struggle to google support for his comment may indicate it's a small effect.
So I'm not convinced, not yet anyway.
Last edited by JamieTrek; 05-04-2017 at 04:22 PM.