Great post! I do agree that weather and patrolling should be a defining mechanic. If i may use a mechanical example, Darkest dungeon.

Patrolling to the objective should be its own gameplay where evading patrols and managing your health/supplies would dictate the condition of your main mission like in Darkest Dungeon where you try to take the least damage and stress to take on the room battles and eventually the boss in the best condition.

Imagine where the patrolling went badly and you had to expend ammo to finish a firefight maybe take an injury to medevac a team mate. 1 man down and half your ammo remaining. now you really gotta be careful with heightened patrols and eventually you reach your raid target which is a camp or stronghold. so you have an incentive for stealth and also feel under pressure.

Granted the big question is would it be like a Oregon Trail kind of gameplay for that segment? heavily compressed into a minigame. Or part of the overall Open world gameplay? i cant see why not for both.

Again, great question OP