Plan for the worst when you're looking for jacket that you'll wear into the mountains. You want a jacket with fabric that boasts a high waterproof rating of 20K or higher and a highly breathable membrane, ample durability, and a construction that includes fully taped or welded seams.
For backpacking, you don't need many bells and whistles. If you're climbing, then you'll want good wrist closures and a helmet-compatible hood to seal out a storm.How to Choose a Shell Jacket
Because these jackets have to fit comfortably when you're wearing backpack or climbing harness, they tend to have a slim to regular fit. Be careful not to choose a fit that's so slim or a size so small that you can't add extra baselayers or an insulating layer.