When going through a newly built nether portal to the overworld the exit portal will almost always generate in a cave if there is a snowy biome at that location.

This is because nether portals require 4 blocks of solid material and air blocks above.
Snow layers are not considered solid and are also not air blocks.
I believe the original intention was to spawn a portal on the surface if possible.

Reproduction steps:

• Generate a world with seed 4979821127687821401
• Run /execute in minecraft:the_nether run tp @s -295 76 309
• Build a nether portal
• Go through
• Notice you end up in a cave instead of on the surface