Weather

In clear weather terrain is normal and everything is relatively easy to see.

Extreme cold bites through straight to the bone, freezing a creature’s blood in their veins and granting them a cruel and macabre death. While in extreme cold, a creature takes final freeze damage every hour depending on their state of dress: if they are wearing no or light clothes, they take an amount of freeze damage equal to 30% of their maximum Health; if they are wearing Light armor or a moderate amount of clothing, they take 20% of their max Health as freeze damage; with Medium armor or somewhat thick and heavy clothing, they take 10%; and in Heavy armor or very thick and heavy clothing, they take 5%. If wet flesh makes contact with extremely cold metal, the flesh becomes stuck to the metal until either a. the metal is warmed up enough for the flesh to become unstuck or b. the flesh is ripped off, dealing anywhere between 1 and 1d10 true damage depending on how much flesh was stuck.

Should a creature be traveling through an area of intense and extreme heat, they will take final burn damage every hour depending on what they are wearing: if they are wearing nothing or light clothes, they take an amount of burn damage equal to 10% of their maximum Health; if they are wearing Light armor or moderate clothing, they take 20% of their max Health as burn damage; for Medium armor or heavy clothing, they take 30%; and for Heavy armor or very thick and heavy clothing, they take 40%. If a creature is taking steps to help cool themselves off, such as wearing reflective clothing or drinking twice the regular amount of required water, they take the next lowest tier of damage, to a minimum of 5%.

Fog has the interesting quality of being equally opaque to those seeing in both the visible light and infrared spectrums, and because it is not a form of darkness, dark- or low-light vision of any kind does not have any effect on it. Because of this, it effectively makes all who wander into it equally blind. How blind, of course, is a matter of how thick the fog is, which the GM can decide arbitrarily or roll on the following table to determine. Fog also has the unique quality of being able to be dispersed by a strong enough wind, depending on the volume of the fog and the strength of the wind, of course.

d4	Fog Thickness	Visibility
1	Mild	30 meters
2	Moderate	15 meters
3	Thick	5 meters
4	Severe	<1 meter

Skill Checks
Navigation. Given how difficult fog makes it to view the surrounding landscape, fog is an especially difficult obstacle for a party navigating through any but the most familiar of terrains. Each level of fog increases the Navigation check DR by 6, and Thick and Severe fog causes the check to be made with disadvantage.
Perception. Sound and smell-based Perception checks are unaffected by fog. Sight-based Perception checks made to perceive something within half of the given visibility are made normally, while those between half of the given visibility and the full given visibility are made at disadvantage. Outside the range of the given visibility, sight-based Perception checks automatically fail.
Survival. Survival checks in Mild and Moderate fog are unaffected, while Survival checks in Thick and Severe fog are made at disadvantage.
Attacks
Melee. Melee attacks are unaffected in all types of fog except Severe, wherein they are made at disadvantage.
Ranged. Ranged attacks are made normally if they are against a target within the fog's given visibility and at disadvantage otherwise. If the attacker cannot see their target due to the fog, this would apply two instances of disadvantage, causing all of the damage dice to be automatically taken at their minimum value.

Hail, in addition to being an obstacle for Perception, can also be quite dangerous, not just because it physically batters those caught in it but it also makes for uneasy footing. Because of this, in an area affected by hail, any creature that moves on foot at faster than half their regular walking speed must make a DR 16 Reflex save to avoid slipping and falling prone on a loose chunk of ice. Additionally, affected creatures take varying amounts of freeze/physical damage at the start of their turn depending on the intensity of the hail, as given in the following table. This damage is reduced only by the affected creature's Armor score.

d4	Hail Intensity	Damage	Visibility
1	Light	1d6	1km
2	Moderate	2d6	250m
3	Thick	3d6	30m
4	Severe	4d6	5m

Skill Checks
Navigation. In addition to being a painful nuisance, the clouds and snow that come with hail also make it difficult to navigate through. For each level of hail intensity, the Navigation check DR increases by 3.
Perception. While hail doesn't affect smell-based Perception checks, it does affect one's ability to see and hear. Sight- and sound-based Perception checks made to perceive something within half of the given visibility are made normally, while those between half of the given visibility and the full given visibility are made at disadvantage. Outside the range of the given visibility, sight- and sound-based Perception checks automatically fail.
Survival. Survival checks in Mild and Moderate, and Thick hail are unaffected, while Survival checks in Severe hail are made at disadvantage.
Attacks
Melee. Melee attacks made in Mild and Moderate hail are unaffected, whilst in Thick and Severe hail, they are made at disadvantage.
Ranged. In Light and Moderate hail, ranged attacks are made normally if they are against a target within the hail's given visibility. In Thick and Severe hail, ranged attacks are made with disadvantage inside the range of the hail's visibility, and outside of that range have another instance of disadvantage applied, causing all of the damage dice to be automatically taken at their minimum value.

During lightning storms, any hearing-based Perception checks are made with disadvantage, and visibility is reduced to just a few kilometers. Should a creature be struck by lightning (which has a 1% chance of happening at the time the lightning strikes), they take 4d6 electric damage reduced only by their Natural Armor.

While the dreary grey clouds of an overcast sky don't hamper much, they do block the Sun's light, lowering the brightness of everything in the affected area to the next lowest level.

Rain with greater intensity than a Drizzle causes everything in the immediate environment to become slick, creating difficult terrain where appropriate, such as slippery cobblestones, sloppy and thick mud, or slick and slushy snow and ice. It also lowers visibility and douses unprotected and non-arcane flames according to the following table, which the GM can roll on or pick from as they desire when it starts raining. How long the rain lasts, and how it changes overtime, is up to the GM to determine.

d4	Rain Intensity	Visibility	Flames Extinguished
1	Drizzle	1.5km	Tiny
2	Shower	1km	Small
3	Heavy	250m	Big
4	Downpour	30m	All

Skill Checks
Navigation. Navigation checks made in Drizzle and Shower rain are unaffected, while those made in Heavy and Downpour rain have their DR increased by 5 and 10 respectively.
Perception. While light enough rain is not much of a hindrance, sufficiently intense rain can hamper all types of Perception checks. Drizzle and Shower rain does not affect Perception checks, but for Heavy and Downpour rain, all Perception checks made to perceive something within 1/10th of the given visibility are made normally, while those between 1/10th and half the given visibility are made with disadvantage. Perception checks made to perceive something further away than half the appropriate level of visibility automatically fail.
Survival. How rain affects Survival checks depends on what the check is attempting to achieve. For finding food, Survival checks are unaffected by all levels of rain. For finding water, Drizzle and Shower rain do not affect Survival checks, while Heavy and Downpour rain cause them to automatically succeed. When tracking creatures or groups, Drizzle rain does not affect the check, while Shower, Heavy, and Downpour rain increase the DR of the check by 3, 6, and 10 respectively; additionally, Survival checks to track a creature or group made in Downpour rain are made with disadvantage.
Attacks
Melee. Melee attacks are unaffected in all types of rain.
Ranged. Ranged attacks are made normally if they are against a target within the rain's given visibility and at disadvantage otherwise. If the attacker cannot see their target due to the rain, this would apply two instances of disadvantage, causing all of the damage dice to be automatically taken at their minimum value.

Similar to rain, snow that is of Moderate or greater intensity creates difficult terrain in the affected area as everything becomes covered in snow and ice. Although snow typically takes time to build up and cover the ground, assume for gameplay purposes that the requisite amount of snow buildup for it to have an effect on gameplay is 1 hour for Light snow and instantaneous otherwise.

d4	Snow Intensity	Visibility	Flames Extinguished
1	Light	1.5km	Tiny
2	Moderate	750m	Small
3	Heavy	125m	Big
4	Blizzard	15m	All

Skill Checks
Navigation. Navigation checks in Light snow are unaffected, while those made in Moderate, Heavy, and Blizzard snow have their DR increased by 3, 6, and 12 respectively.
Perception. Unlike rain, snow typically only hampers sight-based Perception checks, though heavy enough snow can affect sound- and smell-based checks as well. Perception checks made in Light and Moderate snow are made normally, while those made in Heavy and Blizzard snow are made with disadvantage within the range of the given visibility, and automatically fail otherwise.
Survival. How snow affects Survival checks depends on what the check is attempting to achieve. For finding food, Survival checks are unaffected by all levels of snow. For finding water, Light and Moderate snow do not affect Survival checks, while Heavy and Blizzard snow cause them to automatically succeed provided the checking creature has a means of melting the snow. When tracking creatures or groups, Light and Moderate snow actually make tracking easier, since creatures leave tracks in the snow that won't be covered up for some time (24 hours for Light snow and 12 for Moderate) - this results the DR of the Survival check to decrease by 3 for Light snow and 6 for Moderate, though if the tracks are obvious enough there likely won't be a need to ask for a check at all; for Heavy snow, tracks will become filled in/covered up after only an hour, and for Blizzard snow, tracks disappear after just 10 minutes.
Attacks
Melee. Melee attacks are unaffected in all types of snow.
Ranged. Ranged attacks are made normally if they are against a target within the snow's given visibility and at disadvantage otherwise. If the attacker cannot see their target due to the snow, this would apply two instances of disadvantage, causing all of the damage dice to be automatically taken at their minimum value.

There are 6 types of storms: 1. hail, 2. lightning, 3. rain, 4. snow, 5. wind, and 6. rain & lightning. When a storm occurs, the GM should roll for what kind of storm it is, assuming they did not already have a type in mind, and use the most severe intensity of that weather for the duration of the storm.

Like rain and snow, intense enough wind can douse flames that are neither protected nor arcane in nature/origin. Creatures moving against the wind have their Speed halved, while creatures moving with it have their speed doubled.

d4	Wind Intensity	Audibility	Flames Extinguished
1	Mild	Clear	Tiny
2	Moderate	100m	Tiny
3	Strong	25m	Small
4	Tempest	5m	Small

Skill Checks
Navigation. Navigation checks are unaffected by wind.
Perception. Wind doesn't affect sight-based Perception checks, but smell- and sound-based checks are made more difficult if the wind gets strong enough. With Mild wind, Perception checks are unaffected, whereas in Moderate, Strong, and Tempest wind, sound-based checks have their DR increased by 4, 8, and 12 respectively. For smell-based checks, Moderate wind increases the DR by 6, Strong wind causes them to be made with disadvantage, and Tempest wind causes them to automatically fail.
Survival. Wind has no effect on Survival checks of any kind, but it may make tracking creatures indirectly harder by covering up or mussing tracks.
Attacks
Melee. Melee attacks are unaffected in all types of wind except Tempest, which causes them to be made with disadvantage.
Ranged. Ranged attacks are made normally if they are against a target within half the wind's given audibility and at disadvantage otherwise.