Weather-Locked

The week is the weather is a concept I'm entertaining for my home game campaign.

The premise is that weather is so ridiculously consistent within this campaign world that people can form days of the week out of it. (And without a day and night cycle, the planet being tidally-locked, the basis for a 'day' is far fuzzier anyway.) And because the notion of a week is largely born out of religious or astrological significance, we can incorporate that too.

Hopefully this solves two problems:
1) Not using enough weather effects in my games.
2) Providing opportunities for stealth and deception that nights typically offer.

Depending on which region one is in, the week has a different length. A "Day" in this case simply means somewhere approximately 20-30 of our hours in time, and each day describes the weather effects of that day.

So, for example. Sunday is a sunny day. Monday is a clear day in which the moon is visible. Rainsday is a rainy day. Giantsday is when the storm giants play bowling. Swordsday is when swords fall out of the sky. And so on and so forth.

If a random day is needed, roll the appropriate die.

Source

Feyfjord / Twilight City / Southlands

Climate: Cold Moderate
Inhabitants: Drow, Humans, Undead, Lycanthropes

d8	Day Name	Weather Effects	Mechanical Effects
1	Monday	Western skies clear, eastern skies cloudy. The eternally-eclipsed moon comes into view. Monsters are stronger.	Lycanthropes doubly aggressive. Undead gain 1 temporary HD
2	Fogsday	All lowlands covered in a thick fog and sporadic rain. A time for plotting and sneak attacks.	Fog limits vision to 2d6x10ft
3	Frostday	The fog freezes into an all-covering frost. Sneaking difficult as footsteps crunch underfoot. Portents in the frost formation viewed in auguries.	Make three temperature checks per day if traveling outdoors, DC 3d6. Stealth at disadvantage outdoors. Those skilled in religion and/or nature may make one free Augury today.
4	Thawsday	The frost melts. Trails turn to a sloshy mud.	Roads and paths are difficult terrain.
5	Monday	Western skies clear, eastern skies cloudy. The second Monday is always worse than the first.	Lycanthropes hyper-aggressive. Undead gain 2 temporary HD
6	Sunday	Western skies cloudy, eastern skies clear. A dread day for the drow. Sunny and windy.	Sunny outdoors.
7/8	Darksday	Thick clouds overcast. It is almost like night. A perfect hunting ground for creatures of the Underdark to emerge.	Outdoors considered Dark, light sources required. Underdark creatures seen on surface.

Deadwind Archipelago

Climate: Temperate Oceanic

Inhabitants: Humans, Orcs, Dragons

Roll 2d12, and take the higher result for the maximum number of days in this week (after which number it cycles back to one.)

dX	Day Name	Weather Effects	Mechanical Effects
1	Rainsday	A gentle rain.	None
2	Calmday	The calm before the storm. Windy and foreboding.	Ships move at half speed.
3	Stormsday	Thunderstorms	Those without Storm Clerics or sufficient groveling to Hydur the God of Wind and Vengeance have a 1 in 4 chance of being struck by lightning.
4	Windsday	A day for unusual winds, its 1) Spores 2) Fiber Breezes 3) Smog Mist 4) Ash Gales	Ships move at double speed. Air pollution hazard: make three Constitution checks per day or suffer infection. Missile attacks at disadvantage.
5	Sunday	Clear	None
6	Mishapsday	Clear	Critical fumbles range increased by 2 for everyone and everything..
7	Ruinsday	Dangerous clouds overhead: 1) Cloudkill 2) Shock Nimbus 3) Cumulostratagis 4) Blast Clouds	Those unshielded from sight of the sky by cover, large hat, or umbrella have a 1 in 4 chance of suffering cloud attack.
8	Aurorasday	Aurora Oceanis - lights on the ocean waves caused by the Undersun.	All magic treated as if upcast one level.
9	Tornaday	Wild tornadoes rip through the region. Ships get bunkered down.	1 in 6 chance a tornado will come past your area.
10	Doomday	Completely calm. No rain. Pray, pray for the return of rain.	Dread takes hold. -2 penalty to all Morale rolls.
11	Halberday	It literally begins raining halberds. Better bunker up!	Unless seriously protected, stepping outside prompts attack as if from vorpal weapon every 1 minute.
12	Zud!	Something begins emerging from every natural surface, its: 1) Knives 2) Slime 3) Toxic Bubbles 4) Fire Oil	All islands spontaneously erupt in dangerous substances, like oil bubbling up from the ground.

Chronulus / Wizard City

Climate: Hot Dry

Inhabitants: Wizards

d8	Day Name	Weather Effects	Mechanical Effects
1	Sunday	Sunny, bright.  The Doom Sun radiates all.	Second mysterious sun arcs across the sky. While under its direct rays Save or suffer mutation. High Noon floods streets with mutant creatures big and small.
2	Stormday	Lightning, rain, and plenty of it. Has a strong tendency for targeting the ironic. The wearing of hats tends to alleviate this, the larger and more silly the better.	That which is most ironically affected by rain or lightning must Save vs. Charisma or suffer the effects of a Lightning Bolt. Situational basis.
3	Mayday	Pockets of high and low gravity throughout the city.	The next time someone rolls a ‘1’ on any die, a pocket of high gravity is found: double fall damage and disadvantage on all attacks. Next time someone rolls an ‘8’ on any die, a pocket of low gravity is found: no fall damage or spellcasting while floating.
4	Summertide	Heat waves and toxic algae blooms. The air is stagnant and stinking.	Watery areas bloom with toxic algae. Breathing air by pools produces Save vs. Poison to avoid wretching for 1d10 Minutes. Completely submerging automatically fails Save.
5	Candlewake	A shroud of supernatural darkness covers the city. The recent dead emerge to stalk the dim corners and alleys - candles keep them at bay.*	The city is dark. All ethereal beings become visible and aggressive in said darkness. Strong and magical lights are targeted by the mutant undead for elimination.
6	Payday	Bounced cheques grace the skies like dancing cherry blossoms. They’re all complete garbage, except for the famous Lottery Cheque.	Streets filled with slippery bounced cheques. 1 in 6 chance on running through streets to slip and fall. Cheques also highly flammable - lighting on fire will set streets ablaze. Approximately 1/1,000,000 chance of finding genuine Lottery Cheque (Roll 1 on three consecutive d100s)
7	Saltsnow	Air currents from the east bring the Saltsea down from the sky in big salty flakes.	Grounds become coated in salts. Exposed plantlife withers. Causes irritation on touch.
8	Bloodtide	A dark black blood seeps up from the depths, forming cursed flammable pools at random throughout the city and river.	Any area has a 1 in 4 chance of containing a 25sq ft cursed oil slick - disturbing causes 2d4 1HD muck skeletons to emerge and drag any nearby into the pools to drown.

*This includes many of the mutant creatures which spawn and die during Sunday. Muuuutaaaant Ghooooooosts!