Libramarian
Adventurer
The 1e wilderness survival guide is such a crazy book 
This is what I'll use as the basis for visibility:
Visibility is 2 miles for lowland terrain, 10 miles for sites/treetops, 20 miles for hills, 30 miles for mountains and 40 miles for snowcapped mountains. This is the distance one can see looking out from on top of this terrain, or see this terrain from elsewhere. Terrain of greater visibility blocks the view of terrain of lesser visibility. Sites can be seen from a maximum of 10 miles away, or up to 20 miles with a Perception check. (Basically when comparing terrain to terrain, take the greater value. When looking at a Site, take the lesser value. Sites might require a Perception check in forested terrain, or might be invisible from >1 mile away if they're beneath the canopy).
I like the rules for weather in the DMG: simple but effective. I made a couple tweaks:
Temperature
1: d6 degrees colder than normal, and reduce normal temperature 1°C
2-5: Normal temperature (10°C at game start)
6: d6 degrees warmer than normal
Wind
d6
1-4: Clear
5: Light wind
6: Heavy wind
Rain (snow when <0°C)
d6
1-4: Clear
5: Light rain
6: Heavy rain
Cold: When temperature is below 0°C, DC10 Con check each hour for Exhaustion unless wearing winter clothing or near a campfire.
Campfire: Doubles encounter check frequency when not moving.
Wind: Treat effective temperature as 5° colder in the rain.
Rain: Reduces visibility by half.
Heavy wind: Disadvantage to ranged attacks and Perception checks that rely on hearing. Prevents the party from taking a short rest in clear terrain.
Heavy rain: Light obscurement (visibility <1 mile). Disadvantage to Perception checks that rely on hearing. Extinguishes campfires. Clothes become waterlogged and no longer function as winter clothing until dried out. Heavy snow creates difficult terrain.
This is what I'll use as the basis for visibility:
Visibility is 2 miles for lowland terrain, 10 miles for sites/treetops, 20 miles for hills, 30 miles for mountains and 40 miles for snowcapped mountains. This is the distance one can see looking out from on top of this terrain, or see this terrain from elsewhere. Terrain of greater visibility blocks the view of terrain of lesser visibility. Sites can be seen from a maximum of 10 miles away, or up to 20 miles with a Perception check. (Basically when comparing terrain to terrain, take the greater value. When looking at a Site, take the lesser value. Sites might require a Perception check in forested terrain, or might be invisible from >1 mile away if they're beneath the canopy).
I like the rules for weather in the DMG: simple but effective. I made a couple tweaks:
Temperature
1: d6 degrees colder than normal, and reduce normal temperature 1°C
2-5: Normal temperature (10°C at game start)
6: d6 degrees warmer than normal
Wind
d6
1-4: Clear
5: Light wind
6: Heavy wind
Rain (snow when <0°C)
d6
1-4: Clear
5: Light rain
6: Heavy rain
Cold: When temperature is below 0°C, DC10 Con check each hour for Exhaustion unless wearing winter clothing or near a campfire.
Campfire: Doubles encounter check frequency when not moving.
Wind: Treat effective temperature as 5° colder in the rain.
Rain: Reduces visibility by half.
Heavy wind: Disadvantage to ranged attacks and Perception checks that rely on hearing. Prevents the party from taking a short rest in clear terrain.
Heavy rain: Light obscurement (visibility <1 mile). Disadvantage to Perception checks that rely on hearing. Extinguishes campfires. Clothes become waterlogged and no longer function as winter clothing until dried out. Heavy snow creates difficult terrain.
