It's a blunt instrument that treats a night in the desert the same as a season at McMurdo Sound or an hour on the frozen lake around Satan's genitals or a bad day on the mountainside.
Unspecified variables of shelter, clothing, equipment and morale-sapping accident can adjust dice rolls, damage suffered, time needed to recover etc.
Gaming terms are generic - disadvantage could mean roll-twice-keep-worst or a penalty to the roll; saves are actual saving throws or relevant ability checks; 'Classic Six' Ability Scores should be easy enough to interpret; same for 'proper' names of conditions and spells.
My starting point was 1e AD&D Wilderness Survival Guide, but that's heavy on the tables, the variables and the Fahrenheit. It's there if you want it. Working on the Outer Space hazards gave me some ideas that I've applied here.
As an option, Hypothermia (or just being cold enough) or being in a Whiteout could be Altered States, if that sort of thing is part of your game.
Cold Conditions - An Easy Way.
Fold everything in together and abstract it as follows.
When it's cold, you take 1 (or more) temporary damage to CON, DEX and WIS every time you fail a save - and you make a save every time unit you spend in those conditions, with adjustments to the roll for wearing the proper clothes, or being soaked to the skin, or being a bare-chested barbarian.
The frequency of the save determines the severity of the cold: shorter time between saves is worse.
If any Ability Score hits 0, you collapse and take d6 hits per time unit until you are rescued or you die.
Ability Scores recover at a rate of 1/hour in warmth and shelter.
(You could also mod this for hot conditions - temporary damage to DEX, INT and STR, and recovery requires shade and water)
Cold Conditions - Further Elaboration.
Severity is based on the length of the time units that trigger a save or are counted against your CON (or fraction of CON).
Failing a save or hitting the limit means you suffer harm: -1, -3 then -6 to STR, CON and DEX (does not stack).
Ability Scores recover at 1/hour in warmth and shelter.
If you fail 3 cold saves in a row or hit a pre-determined CON threshold, you will begin suffering from Hypothermia.
For each time unit you suffer Hypothermia, you advance levels of harm:
- Disadvantage on attacks and manipulation (or -2 attack penalty).
- Move rate halved, always lose Initiative, disadvantage on movements and manoeuvres (or slowed).
- Disoriented, disadvantage on CHA, INT and WIS (or confusion).
- Save per time unit or pass out (or damage per time unit).
- Save per time unit or die (or damage per time unit).
Recovery is at the rate of 1 hour per level of harm once you're out of danger - regaining Ability Scores can stack with this if you're being properly looked after, otherwise it all happens in reverse order.
(This only slightly modified subsystem has been cheerfully pillaged from Leicester's Ramble because Vance's is better than the one I was trying to construct from the Wilderness Survival Guide)
Hypothermia and Frostbite do not necessarily go together, but you can use the 3 failed saves in a row or CON threshold methods to determine when Frostbite sets in (or model it after chill metal).
Frostbite has three stages:
- Painful: disadvantage on attacks and manipulation if it's your hands; half move and disadvantage on movements and manoeuvres if it's your feet; treat in 2 turns or it becomes Severe.
- Severe (Numb): take non-lethal hit point damage; treat in 2 turns or it becomes Permanent.
- Permanent: take lethal hit point damage and you lose the body part. Risk of infection doubled until treated, plus new parts of the body are exposed.
Base hp damage on the severity of the cold and the size of the body part.
Timely treatment stops harm advancing. Recovery is 3 turns of proper treatment per level of harm, but that's not going to bring your nose back.
Snow Glare/ Snow Blindness.
When subjected to Snow Glare without eye-protection, it's like you are trying to avoid a gaze attack - apply the appropriate penalties (you at -1 to hit, enemy at +2 to hit you and no DEX, if you don't have something already).
You might still have to take the penalties even with eye protection, as it could obscure your vision in an equivalent manner, but at least you won't have to make a save every time unit (again, the shorter the more severe) or suffer Snow Blindness.
Snow Blindness means you are Blind, but you recover in exploding d6 hours once you are no longer exposed to the glare. Proper rest and treatment can reduce this to exploding d6 turns.
Chances of getting lost are rolled with disadvantage or are rolled twice as often. You must also rest twice as often or twice as long, and you can only move at half rate.
Encounter distance is reduced to minimum. Surprise chances are doubled.
For melee and missile attacks, it's as if you are trying to avoid a gaze attack - apply the appropriate penalties. Missile attacks are at disadvantage (option for crossbows and firearms to be the exception).
In a Whiteout, it's as if everything is invisible and everyone is Blind. Save vs. confusion every time unit you attempt to do anything other than hunker down and wait it out.
|30 Days of Night (2007).|
Other People's Stuff.
These are self-contained systems I've mentioned before, but can be bolted onto any scenario with similar winter survival concerns - as alternative or supplement.
Electricity and Heat in your base is yes/no - for each day you don't have Heat, you take damage or an Injury. Every time you take an Injury, roll over your total on 2d6 or you die.
(Food and Water is counted in units per person per day, with the same result if you go without)
Cold vs. Fuel, measured as units, and Fuel is consumed even if there isn't enough to beat the Cold.
Someone dies every game turn (could be a day, could be a week) when Cold beats Fuel - or you could have a death with no Fuel, but with not enough a person gets Sick.
(Also covers Hungry? vs. Food and Sick? vs. Medicine, but it's only the NPCs that suffer in this mini-game)