d30 Months of Weird Weather

 

by Odd Nerdrum

d30 Weirder Weather-Months:

This is part two of my weather trilogy. In Part One I made up a yearly calendar of weather with each month being composed of a single unchanging type of weather. I explain my reasoning for this in the post. Each weather type had some simple, yet concrete and impactful, mechanical effects - like campaign level status effects. Check it out here. This Weather-Calendar kept it quite straight - a fairly generic seasonal year with a few flourishes but you (🫵) could be much more creative. You've read the title, we're doing weird weather today. I owe thanks to Mikesmix of Sheep and Sorcery, Whisper of Glass Ziggurat and maxcan7 of Weird and Wonderful Worlds for their creative contributions to this list. 

While it is of my opinion that one should use ‘weirdness’ carefully, one can’t always be mundane. THAT’S BORING! Here are d30 other monthly options, they range from reasonable to gonzo. I tried to consider gameplay first, I broke some of the rules I proposed in part one but if you have ideas for better implementation, please suggest! I think weather 11 is my favourite but there are plenty of mechanics in here you can mine and use for other things.

d30 Weird Months of Weather

1. Pollen: The realm is wreathed in a ruffle-petalled raiment of gaudy, blooming flowers. The air is clouded with yellow fragrant spores that settle and form drifts and banks in the spring grass. On character creation roll a d10, on a 1 your character has hayfever and suffers a -1 to all rolls during this sneezesome month, otherwise you are ok. Plant creatures always have maximum HP.

2. Battle: The seasonal struggle between Law and Chaos. The night sky scintillates with the sparks of cosmic battle, the earth rattles and multitudinous rainbows jaggedly streak the sky fading to black and white and back to colour again. All magic cast by Chaotic beings is treated as if cast 1 level higher but Lawful entities’ saves vs all magical phenomena are at +2.

3. The Big Bustard Hunt: Around this time of year, strong and warm westerly squalls blow over desert dust and huge flocks of plump and juicy bustards. While fewer of these dumb, delicious birds get blown over each year, I wouldn't worry about it, get hunting! - the most common encounter on your encounter table is replaced by small flocks of 2d12 Bustards. By the way, each bustard is worth a ludicrous amount of XP.

4. The Haze: Velvety purple vapours cloud the skies and valleys with their cloying, narcotic scent, the grass turns plump, succulent and soft - everyone is high for the whole month as if on a random drug. You can ‘reroll’ your drug by immersing yourself in cold water. Upon resurfacing a new drug is rolled for. This ‘reroll’ can only be done once per day. 

5. Steroid Rain: It rains steroids - everyone is considered to have a Strength score of 18 for the month. Neutral results on reaction rolls (6-8) have a grumpy, macho tone. These heavenly steroids are not potable. 

6. Feeding Season: This annual pseudo-weather event occurs when the man-eating Yateveo plants release their prey hormone - all mammals are considered to have a Wisdom score of 3 for the month and automatically fail saves Vs Paralysis.

7. Portalmas: The air tastes metallic, hairs stand on end. The landscape is littered with vantablack portals - wherever one is, there is a 5-6 chance that one of these portals is within the immediate vicinity. If entered teleport to a random campaign hex. Once entered both ends of the portal collapse within 10 minutes. Criminals love this season.

8. Vampiric Fog: A thin terracotta coloured mist thirsts for blood - damage rolls of 1 deal max die-size damage instead (ie 6 for a d6 weapon) as the drawn blood spins out into the hungry, sucking fog + Death and Dismemberment rolls are one deviation worse. 

9. The Boiling: All unadulterated water boils - rivers, lakes, oceans, the water in your canteen. The month prior all non-immune water-life, sensing the approaching danger fled. The air is filled with steam. Folk prize milk, beer and other such drinks which are oddly unaffected. The effects - splashed boiling water does 1 point of damage, submersion = 1d6 damage per round. Torrid, you must consume one inventory slot worth of some kind of drink to benefit from any kind of healing, magical or otherwise. The steam purifies, +2 saves vs disease. 

10. Drutefall: The long dormant drute plant's fruit pods burst forth from the soil and, geyser-like, expel their stinking gases and saprogenic fruit. The land is carpeted with foul, purple sweating puck-shaped fruit and thick green clouds vein the sky. The effects: the drute’s green gasses rapidly rot all other food stuffs (and corpses) to mush (ten minutes for corpse mushification, regular food stuffs - almost instantly). Only the drute (and canned goods, quickly gulped down) can be eaten. While omni-abundant, drute has no nutritional value and the body can only extract so much calorific value from it. Drute heals only 0-1 HP regardless of how much is eaten during the day. Additionally, all one can smell is the stench of Drute, the DM cannot describe any other smell. Drute tastes like hog-fat fried rubber tires with a citrus twist.

11. The Aggressively Pacifistic Murmuration of Paradoxical Utungo: For the month, the sky is clouded with one vast murmuration of philosophical finches. They’re engaging in their seasonal stratospheric debate. They argue in the language of birds about all things but there is one belief they all agree on… their beady little eyes and black-gold plumage conceal a soul violently dedicated to pacifism. Whenever combat takes place the murmuration reacts! The murmuration takes part in the combat attacking one participant (per 4 combatants) for d12 damage each round of combat. This swarm attack cannot be blocked meaningfully by an unprepared individual and automatically deals this damage. Likewise, the finch swarm is so vast it cannot be meaningfully damaged or repelled. When combat ends, so do the finch’s attacks. Human disputes are settled via ritualised ‘dueling caves’ where they are safe from the murmuration.

12. The Fizz: The air carbonates, a reverse rain of pinkish bubbles percolate up from the buzzing earth and into the hazy, salmon-coloured sky. Likewise, leaves, dust and detritus are carried, floating up, into the air. The rich recline on marble slabs or are carried in sealed sedans as the bubbles do itch. However, for the month, one can jump twice as far/high and falling damage is halved. The bubbles cannot pass through thick non-porous materials, so this effect does not work inside of most stone-floored buildings, dungeons or stoney caves. If sleeping on or above bare earth, one only gains half the usual healing from sleep. 

13. The Sweating: Slick green beads of moisture bud up on all things. The sky goes blotchy, bruised - all chartreuse and plum-coloured. All creatures are unsteady, sweaty and irritable. Critical failure ranges extend by one, average reaction rolls (6-8) in miserly, disgusted or sick moods. Academics are still unsure as to whether this phenomenon is extracting the green ectoplasm from matter or merely depositing it upon things. 

14. Black Sun, Bright Moon: The Month in which (as legends tell us) Lord Sun and Lady Moon agree to swap roles, swap clothes, swap souls but retain their minions. The Sun turns black and plunges the land into a shivering, quivering pseudo-night and the Moon radiates a brilliant white light that bathes the world in a sterile glow. Day and Night have swapped illumination! Day/Night encounters remain the same but suffer -2 to their encounter roles as they resent the unnatural light. Dreams now occur during waking hours so the DM is free to add individualised hallucinations when and wherever they see fit.

15. Month of the Living Dead: A silvery mist descents upon the land and curls, coiling tendril-wise along the ground (ranged attacks cannot be made beyond 60ft). The sun turns dim and the moon glows a blood red. The tree's bare black branches knot themselves and no wild game can be hunted, for it has all fled the unnatural, necrotic stillness of the air. Any slain creature rises from the dead as a zombie after 1 round unless its brain is destroyed. 

16. Acid Rain!: Acid rain. You know what it is. But how does one protect against it? Alkaline grease pots! They cost 1 gp and grease 1 item. Pots can be stacked 10 to an inventory slot. Greased items are protected for one entire journey through the acid rain (only). Any unprotected items receive the ‘acid-etched’ descriptor (or just an X on your character sheet), if any ‘acid-etched’ items are damaged again by the acid rain they become ‘corroded’ (or XX), if a ‘corroded’ weapon is unprotected/ungreased in the acid rain it is destroyed. ‘Acid-etched’ items can be repaired, ‘corroded’ weapons cannot. If a ‘corroded’ weapon receives a notch it is instantly destroyed. Some cheapskate players will try to hide things in greased bags, sure, just don’t take their contents out in the rain.  

17. Radioactive Death Cloud: The southern wind blows down nuclear fallout from the ruined and wasted northern hemisphere around this time of year - big comically green clouds of the stuff with its geiger-counteresque clicking - you’d better put your gasmask on. At character creation, roll your character’s maximum age, perhaps 50+2d20 years. Everytime a player whose character does not have a gasmask (with filter) rolls a dice, their character loses 1 year off their maximum lifespan. Filters cost 1 GP, take up one inventory slot and last one day once removed from their protective seal. Filters are destroyed by water, falling damage and damage rolls of 1. Characters die should their current age exceed their maximum age. During this month, each Death and Dismemberment roll is supplemented by an additional roll on your mutation table. An expensive RadAway equivalent might be able to restore lost lifespan. 

18. The Death-Defying Breath of the Green G-d: The sky turns a clear and vivid cyan. The Green G-d exhales, its breath - a hot, dewy murmuring wind that flows through all living things, filling them to the brim with vitality and health. New growth whips and tangles, beasts are born big and bellowing. Effects: saves vs death and dismemberment are one deviation better, sleep heals double the usual amount, forest hexes and similar are treated as very difficult terrain as they swell densely with thorns, tangled branches and berried thickets. Monsters have as a minimum their average HD’s worth of HP.

19. The Not At All Horrifying and Actually Quite Delicious Gravy Drizzle: The sky turns the deepest brown (vantabrown), black shapes dart between the cloudbound rivulets of ‘gravy’. A mysterious beefy mist buffets the landscape and those who dare walk in its salty, fatty slickness. It’s warm. The plant world dislikes this moisture and most vegetation shrivels considerably. Water tastes bad. Animalia loves it as the meaty dew is very nutritious. Food stuffs coated in the brown translucent spray heal an extra +2 HP. Predators, satiated, have +2 to their reaction rolls - they’re not hungry. However, if the PCs are coated with gravy, bite attacks performed against them deal damage equal to one die size higher than normal (as the characters have become tastier). 

20. The Greyful Hum of Taos: In this dry month of winter, having burrowed up from their grey trackless dunes on the far side of the earth, come the Achromicidae - a cacophonous swirl of swarming locust-like insects, vast as to dim the sky. It is not crops the swarms will devour but colour itself. For this month the DM cannot describe colour at all beyond black, white and shades of grey. Additionally, the hum-chittering of the swarm is almost unbearable, so overpowering in fact that the DM cannot describe the sound of things beyond sight of the party. Elves are not so affected by these effects they can still see colour, albeit somewhat desaturated and noises, while audible are muffled and indistinct. Characters cannot gain the full benefits of sleep without earplugs. 

Extra Weird Weather Submissions:

Here are submissions from my creative friends, Mikesmix of Sheep and Sorcery (entries 21-26), Whisper of Glass Ziggurat (entries 27-28) and maxcan7 of Weird and Wonderful Worlds (entries 29-30). The bracketed mechanics are of my own devisal.

21. Anti-Rain: Moisture is drawn out of living things and back into the sky.  (Drink fluids to heal as with Scorch in part 1)

22. Oobleck: Black goop. Drowns everything in sticky inedible goop. A curse left behind by a king who refused to accept the world on its own terms. (Increase a Saving Throw of your choice by 1 for each hour spent in the Oobleck. Should a saving throw reach 20 you start to drown. It takes 1 hour of cleaning to recover 2 points of your Saving Throws. High is bad for Saving Throws remember)

23. Chaos Storm: Magic is broken. The world is angry. It rages for the injury done to it by reckless mages who bent the world until it broke. Now magic pure, chaotic and furious rages over the surface. It could do anything to you, anything bad that is. (All characters roll a random curse from your curse table. They are afflicted by this curse for the day. A new curse rolled the following dawn. Likewise, random encounters are also burdened with a random curse. One can purchase lucky talismans that when crushed allow the one doing the crushing to 'reroll' their curse)

24. Fog of War: With the fog comes the ghosts of those who died in an ancient war. They continue to fight their war again anywhere the fog appears. (Whenever combat occurs either side is aided by 1d6 1HD semi-spectral soldiers (or a detachment in ItO style games). Ranged combat has a maximum of 30ft. The chance of getting lost increases by 1 deviation)

25. Vengeful Cloud: You offended this cloud somehow and now it's following you and hitting you with the worst kind of storms it can. (This sentient, rancorous cloud only targets players that perform or act in certain predetermined behaviours that the cloud dislikes such as impoliteness/impiety/bad taste etc. Targeted characters are affected as in Rain in part one. Whenever a player exhibits a certain disliked trait, displeased thunder is heard. They can seek reprieve from the storm by apologising to the cloud. If they apologize for the wrong behaviour they are struck by lightning for 2d12 damage. The cloud's whims change per week)

26. Cloud Giant War: Enormous weapons and gore come crashing down from overhead as cloud giants duke it out. (Every turn of combat drop a number of dice of two types/colours onto the battle map equal to the number of players. The first type of die represents giant's blood, should the dice land on a player/NPC token they must pass a save Vs Death or be knocked prone. If the other die type lands on a player/NPC they are squashed by a shard of the giant's weapon/armour and must save Vs Paralysis or suffer 1d6 damage. Not sure about this one, any other suggestions?)

27. Hypergravity: Mother Earth becomes envious. For the duration of the month, fall damage is increased and nothing can lift itself from the ground.

28. Radio: Metal objects act as receivers for extraterrestrial pop songs, ads, and talk shows. Stealth is impossible if you have any metal on your person, but once per rest you can learn the answer to one question about 1d6: 1) local politics 2) automobile maintenance 3) insurance products 4) romance 5) medication side effects 6) Taylor Swift. (or any 6 topics of your choosing. Obviously)

29. Humboldt Fog: When Pan and his orgiastic party ascend Cypress Grove, their orgone energy summons the blue ribbon bridge to the moon. The milk of their orgy floods the moon and ferments, then melts like fondue back down to the world. The gamey goat cheese flows with abundance and many cultures engage in festivities around the vent akin to a debauched Christmas. (Characters move and hex-crawl at half speed as they wade through the celestial cheese-stuff. Fall prone and become trapped until a save Vs Paralysis is passed. Engaging in hedonistic activities heals a minimum of 1d6 HP. Cheese rations are infinitely available but appear disgusting once the month is over)

30. Gray Goo Greenhouse: Gray goo particles permeate the sky, augmenting and entrapping echoes of ideas that expand like heat through glass. Reality comes apart like a frog boiled in increasingly warming water. Those trapped within a Gray Goo Greenhouse rarely realize what's happening to them. The goo like microplastics, slowly congealing within their brains and minds. (All players, NPC's, monsters, random encounters, items, all inanimate objects infact and some concepts - all roll a random insanity for the month. That or all your players must smoke/inject a nasty and synthetic drug of your choice for sessions that take place during this weird weather month)

Try playing in a game with this as the calendar!

Odd Nerdrum

Another Rambling Postscript:

Again, as I rambled about in Part 1, the benefit of the month-long weather format over the random roll is that it gives players time to internalize the weirdness of the world rather than being constantly shaken about by dozens of short, weird phenomena (that even the world itself barely has time to react to). If that kind of play persists, the players will eventually become inured to the world’s fantasy and any future high strangeness might lose its charm.

Stay tuned for Part Three, Weather Festivals!

Calendar-Weather/Weather-Calendar

The Cloud, Odd Nerdrum

I asked myself, "Why must the Weather change?"

The weather and the calendar are one and the same. 
13 Weather-Months of 4 weeks each. 364 days. No randomisation. No weather rolls. 

Each month is named for its constituent weather. Each weather’s effect lasts for that month only.  

1. Chill 

Quiet, still and colourless. The stinging cold bites at exposed skin and slows the limbs.   

- When out in the cold wear a warm coat* or reduce your maximum HP by -1 per HD (to a minimum of 1). When warm, restore your max HP to its previous amount.

2. Rime 

Frost blooms across the world like a deathly moss. Hearts work hard to warm the body.

- Wear a warm coat and one other item (hat, scarf, gloves, etc) of warming clothing. For each missing item, reduce maximum HP by -1 per HD (to a minimum of 1). When warm, restore your max HP to its previous amount. 

- Bodies of still water, like ponds and lakes, have frozen over but may crack under weight. 

- If soaked wet you die within the hour unless dried and warmed.

3. Snow 

Snow falls thickly. Thrown water freezes in the air. Icicles fruit the trees. Blood runs cold.

- Wear a coat and two other items of warm clothing, or -1 HP per HD for each missing item - up to -3 to MAX HP per HD.

- Overland travel takes twice as long. 

- All still water, rivers and some calmer ocean hexes have frozen over solidly.

- If soaked wet you die within 10 minutes unless dried and warmed.

4. Rain

The cold breaks as the snow is washed away by cool downpours. Nature shivers to life.

- If you spend 10 minutes in the rain you become wet. -1 to all rolls until you have dried yourself. A wool coat will gives one an additional 10 minutes of protection. 

- You become automatically ill if you sleep while wet.

- Chunks of snow, ice and slush are still melting away during the first week of Rain.

5. Mild

Trees bud green, shoots sniff the cool air. Farmers sow in the churned, dark and damp soil. 

- It's just a nice month, no bonuses or maluses

- Foliage is restored during this month, lasting until Fog.

6. Pleasant

Dew in the morning. Blue skies and white clouds patchwork the skies. Blossom falls softly.

- Inspired, for this month gain a +2 modifier to your lowest stat.

7. Sun

Glory! Skins bronze and nature sings, thrumming with life. 

- Everything is great. For this month gain a +1 modifier to all your stats.

8. Scorch

The earth cracks, wisened it thirsts and crumbles to dust. Beasts succumb or seek shade.

- You really shouldn’t travel between hexes during midday¹. If you attempt to, Save Vs Death or collapse on 0 HP. On a successful saving throw you make it, but the journey takes half of your current HP.

- You must consume one inventory slot worth of water to benefit from any kind of healing, magical or otherwise.

9. Thunder

Under dusty, lightning-veined skies; the dry, electric atmosphere belies a violent redolence.

- Critical Hit ranges are extended by one for all combatants. For dramatic games, critical hits are always coolly backlit with lightning strikes.

10. Humid

Wet heat builds. Mosquitoes swarm and contagion spreads in the heavy foetid air. 

- Without a day’s dose of expensive medicines (50gp per day), one automatically fails saving throws against disease, sickness and nausea.

- You must consume one inventory slot worth of water to benefit from any kind of healing, magical or otherwise.

11. Reprieve

Creation exhales. The sun spins out its final rays of strength above the yellow-flecked trees.

- Heal maximum HP from sleep (ie if regular sleep heals 1d6 HP, during Reprieve it always heals 6).

12. Harvest

The leaves droop heavy and coppery. The leaf-strewn fields are lined with bushels of grain.

- All fresh food stuffs heal +2 HP.

13. Fog

The ochres of Harvest give way to grey. The trees turn black and bare. Fog consumes all.

- Ranged attacks have a maximum range of 30ft.

- The chance of getting lost while hex travelling increases by one deviation. 

- Most vegetation is bare until Mild.

*On Coats and Warming Clothing:
These items always take up one inventory slot, even hats, gloves, scarves, bandanas and earmuffs. Though fine coats might count as two warming items despite taking up one inventory slot. Fur armour is also a godsend during the winter. 
A critical hit destroys one item of warming clothing. As does each instance of appropriate elemental damage, a blast of fire - even for 1 point of damage would destroy your coat, a splash of acid would destroy your earmuffs, etc. 
Whenever a character is reduced to 0 HP all items of warming clothing are assumed to be damaged beyond repair or destroyed.
-1 HP per HD means a level 6 character’s maximum HP would decrease by 6 if unprotected in the cold.

Hows and Whys - presented via incoherent babbling (optional reading):

• I made a bad weather system. While trying to think up some other, newer, 'better' method I was left asking myself ‘Why must the weather change?’
• You see, rolling for random weather per day, or even multiple times per session, is just another burden on my tiny brain. I could spare myself and my players this cognitive load niggle by just not doing it. But I still wanted weather.
• Another ‘problem’ with rolling for weather is that some weather types might be so rare as to never be encountered.
• Additionally, is random/changeable weather really that important? Why should the weather change session to session, or even mid-session? WHY? IMPORTANT? WHY? HUH?
• This weather can and is managed via clothing, equipment and gear. Another reason for your inventory and encumbrance systems to matter. 
• Players act on known information, if they can predict the weather they can make plans around it. If they want to carouse through the worst of the winter months, good! Spring and Summer is the perfect time to adventure. I’m not ever memorising a hex-flower however neat they are. Please forgive me 🙇‍♂️.
• Weather control spells become meaningful with monthly weather. Now, even nondramatic weather types have mechanical effects = ‘I can prevent my friend from dying from exposure by making it sunny’.
• The more weather types there are, the more the players must remember. Especially if the weather is very changeable. That’s not a good recipe for player memory. Too few and it will become boring. Longer, more predictable stretches of weather (with effects that try to balance impact and simplicity) should fare a bit better for everyone at the table.
• The clothing management in winter is the trickiest thing IMHO, but it is spread over 3 months/12 weeks of in-world play. That should be enough time to internalise the system without it overstaying its welcome. If you have alternative ideas, suggest them please!
• I didn’t want weather to become irrelevant to higher level players, with characters who could just tank certain effects. I don’t care if you’ve slain the eel-god, fought off armies with nothing but a rusty trident and looted all the jewels of 99th Dimension, if you walk around unprotected in arctic conditions you are going to have a bad time.
• I didn't want to affect stats via stat damage. It's just too fiddly (even for a semi-casual games) to remember to alter values that depend on a given stat or modifier to be worth it. HP is constantly going up and down (max HP less so) but it's something players are used to constantly adjusting. Other bonuses/negatives are static - flat - and last the whole month. 
• That said, in my experience players are more likely to remember positive bonuses to their stats - as with the optimising effects of the nicer summer and spring months. 
• I’d endeavour not to rule any additional mechanical effects/impacts for weather types any more than is necessary. The weather effects are expressly not simulationist, they're gameplay forward. Simulation can be a rabbit hole of needless boredom. 
• The weather cycle I have presented is not very realistic. Humidity should precede Thunder but I sided with what I think would make for better gameplay. Your weather-calendar would look different to mine
• Why is the weather always in 4 week blocks? What is the reason? Who cares, Nerd! Anything is possible in the fantastical world of Dungeons and Dragons™! 
• Long periods of weather allow you (🫵) the DM to consider how the world and its inhabitants react to and live with that weather, any kind. Don't forget to always describe the weather conditions. I tie this to my overloaded encounter die, which as a 'describe the scene' result. 
• 4 weeks seems like the right length of time to me, 1 week is too short, any longer would start to become a drag.
• Speaking of the fantastical, I’ve presented some relatively mundane types of weather. However, the benefit for weather patterns lasting for entire months is that even weird weather can be made understandable, cognizable and verisimilitudinous. Check part two for some weird weather.

If you have better suggestions for distilling these, or any other, weather types into simple, flavourful rules please share!

Month Names:
One may keep the weather names for each as is - named for their weather, ie Harvestmonth or just Harvest. It does aid memory. However, you could rename them. The oldschool worldbuilding trick of translating the weather words into another language still works! They needn’t be direct translations - assonance is king. Here's some Danish, Tamil and good old fashioned Latin month names:

1. Kølige - Kuḷircciyāṉa - Algus
2. Rim - Uṟaipaṉi - Gelum
3. Snevejr - Paṉippoḻivu - Nix
4. Regnfuld - Maḻai -  Pluvia
5. Blid - Lēcāṉa - Mollis
6. Behagelig - Iṉimaiyāṉatu - Jucundus
7. Solrig - Cūriyaṉ - Solis
8. Svie - Eriyum - Letalis
9. Torden - Iṭi - Tonitrus
10. Myg - Īramāṉa - Culex
11. Tilbageholde - Vilakku - Dilatio
12. Høst - Aṟuvaṭai - Ceres
13. Tåge - Mūṭupaṉi - Caligo

Weird Weather in Part 2 (It's Here!), Weather Festivals in part 3 (watch this space).  

¹: Thanks to Jenx of Gorgon Bones for the suggestion. 

A painting of my wife and I at rest. Yet I rise from my stupor having thought of a good mechanic for representing a certain type of weather. In truth, I am deluded. Please don't use this artwork to dox me.
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Actually, The Black Cloud by Odd Nerdrum

Experimental Meta-Weather Rules

Weather. I've wanted a weather system that possesses the following qualities: is simple enough to be memorable, allows for the weather to be naturally and randomly changeable AND stay the same for long stretches, to show weather patterns/trends within a season and most importantly allow for the weather to become 'weird' so that the players can experience wild or dramatic weather phenomena (but not too often) and to try to do all this with as little die rolling as possible. With these criteria in mind, I tried to make a weather system that could achieve them. I don't feel entirely satisfied or successful with the result, the system is more complicated than I would like and janky at times. I am sharing for posterity as I think it's kind of interesting and for the RPG Blog Carnival. I'd love suggestions on how to make the idea that little bit more workable while retaining those design goals. There is a summary of the system at the end of this post.

(All shall be explained)

Find the other season lists here

The system works off of seasonal weather lists. They are 2.?D as opposed to hex-flower weather systems that are 6D.  This system is both more and less predictable than hex-flower weather systems. The weathers are arranged on the table from colder and wetter weathers to hotter and dryer ones. In hot/dry seasons like summer, the wet/cold weathers may not be particularly wet or cold and vice versa. Each weather should logically flow into the next, and the most common weathers will be found in the middle of the table. I have not strived for realism. Adjacent to each weather is a type of weird weather phenomena that could reasonably emerge from the mundane weather it is twinned with.

But how does it work? Place a marker on the current weather in your game (I used a matchstick) and, when you are asked to make a weather check, roll a d12. There are a number of possible results. On a result of 1-2 or 11-12 the current weather will remain the same. On a roll of  3, 4, 5 or 6 the weather will move one increment toward the wetter/colder end of the table, moving from a 10 to a 9 for instance. On a roll of 7, 8, 9 or 10, the opposite effect will occur and the current weather will move one step toward the warmer/dryer end of the table, IE from a 7 to an 8. If the weather cannot move up or down, i.e. is at 3 or 10, then the weather remains the same. 

Should the number that matches the current in-game weather be rolled, it indicates a sudden change. Roll the d12 again and change the weather to that result. If the new roll results in either 1, 2, 11 or 12 OR the same number as the current weather, then the weather will become weird. If the weather becomes weird, move the marker on the current weather one column to the right onto its matching weird weather. Once the weather becomes weird, roll weather checks as normal. Rolls of 1, 2, 11 and 12 results continue the weird weather. Weird weather is detailed a little more later in the post. 

But wait! There's more! In real life, over the course of a season there can be several periods of high and low temperature and dry/wet humidity. In order to replicate these kinds of weather trends I have once again gone META or more accurately (I think) extra-diegetic. Real world weather is taken into account when making weather checks using this system. The real-world weather the day of your game is used to modify the results of your in-game weather checks. The wetter, hotter, dryer or colder a day is compared to the average day of the season you are in, the wetter, hotter, dryer or colder your in-game weather will become. If a weather the day of your game is wetter/colder than usual; apply a -1 or -2 to your weather check, if the day is hotter/dryer than usual apply a +1 or +2. These positive/negative modifiers give the feeling of weather patterns. As a reminder, unmodified rolls of 1, 2, 11 or 12 always result in the weather remaining the same, but rolls that are modified into these ranges do not cause the weather to remain the same, simply changing one step in the relevant direction. Optionally, such rolls can cause the weather to change by 2 steps in the relevant direction. If the campaign is happening during the winter but being played in summer, this is fine. You can have hotter/dryer spells and wetter/colder spells relative to whatever season you are in in-game. 

But, what happens on game days where the weather is weird? When you have sessions on during heatwaves, cold snaps, hail, Saharan dust clouds, unexpected snow, eclipses? On such days the the probability of your in-game weather becoming weird increases dramatically. On 'weird' days, (until a weird weather results is procured) weather checks have the following results - on the roll of d12, a 1, 2, 11 and 12 do not result in the weather remaining the same but becoming weird, as does rolling the number that matches the current weather. As above, when making weather weird, move from the current weather to the right, onto the matching weird weather phenomena. On 'weird' days, the chance of the weather becoming wild or weird becomes 5/12. On normal days it is something like 5/144 (but I'm really not sure about the math for this). Once the weather has become weird, make weather checks as normal and is detailed above. 

How does weather stop being weird? Whenever the weather changes - moves up or down as a result of 3-6 or 7-10. Usually, the weather moves diagonally, up or down, to the mundane weather column. Many weird weathers will have lasting after-effects - such as flooding and wildfires.

I think that's everything. Here are the example seasonal weather tables. I haven't come up with mechanical effects for the different weathers as I am not sure of the viability of this system yet. I have rolled up a month's worth of summer weather using real-world weather data. I assumed one game session a week, rolling for three in-game days of weather per session. As you can see there are three different trends in this 30 period, a warm beginning followed by hot and humid weather in the middle of the month and then a dramatic week of thunderstorms. The bold days are when the weather changed as a result of a reroll and the Lightning Storm phenomena came about as the result of the influence of real world weird weather. 

Summer:

Here are some additional thoughts and optional rules:

• Seasonal weather tables can easily be turned into regional weather tables. Weather might be worse in the mountains, very different in a coastal deserts and rather peculiar in the worm-wastes.  
• It may be worth having a 'weather-master' or 'forecaster' player who is responsible for the tracking and rolling for the weather, just as you might have a mapper and caller. This would help to reduce your mental load. Some players enjoy such rolls and are all are motivated by a 100xp reward for doing them. It would also encourage the players to learn the weather system and become more experienced at forecasting like their characters would. 
• Mundanity is often necessary in fantasy role-playing games. Nothing seems as weird or special if the everyday baseline is already so foreign and removed from the player's lived experience. This applies to weather. Instead of a sun, having a neon-pink, glowing ball of tendrils might sound cool, but unless you mention it a tedious amount your players will forget about it. If the sun turns into something abominable for a week, that's cool and memorable. As a player, one of my best and most evocative memories of weather was when the party got lost in heavy rain in the middle of the night without any shelter. 
• Being very experimental, I would consider a weather phase during combat. Just as some rules have phases for magic, missiles, movement and melee there could be a phase for weather. This phase would see combatants deal with the weather and allow for the weather to act on and in the scene. For example; repeatedly prompting saves against heat exhaustion, seeing snow devils move around the combat map, see if a rain shower starts, how high the flood waters rise or where the lightning strikes. There are many options for weather to take more of an active and present role in combat encounters and the game as a whole.
• When to roll weather checks? That is up to you. Some roll them once per day, others integrate it into their wilderness encounter rolls/checks. I would have weather checks made at regularly times of the day - dawn, midday and dusk and once per day during downtime.
• The 'meta' aspect need not be limited to how hot/dry or wet/cold a day was. It can be linked to anything; windiness, amount of bugs you saw, how well you are feeling, how cloudy the day was. Having it solely based on comparative temperature/humidity limits excludes game-masters who live in equatorial countries. 
• These weather lists make for good rumour and spell fodder.

Summary:

Weather check:

• Roll a d12, considering the real-world weather, if hotter/dryer than usual add +1 or +2 to the result, if colder/wetter than usual -1 or -2 to the result. 
• Unmodified results of 1, 2, 11 or 12 result in the weather remaining the same. If modified into these ranges, treat the result as below;
• If the roll results in 6 or less the current weather decreases by 1 step. 
• If the roll results in 7 or more the current weather increases by 1 step.
• If the weather cannot move up or down, then it will remain the same.  
• If the roll results in a roll matching the current weather, roll the d12 again: 
• If 1, 2, 11 or 12 the weather stays the same.
• If the roll matches the current weather a second time then that weather becomes weird, moving to the right onto the adjacent weather on weird weather column. 
• If the d12 results in any other number, the current weather changes to the weather that matches that number.
• Once 'weird', the weather remains weird until a weather check moves the weather up or down the table. At which point the weather moves diagonally left, up or down, onto the mundane weather column. 

If the current real-world weather is unusual:

• Roll a weather check as normal. Results of 1, 2, 11 or 12 do not result in the weather remaining the same but becoming instantly weird. Likewise, rolling the number of the current weather causes it to become instantly weird.
• Once the weather has become weird, make all subsequent weather checks as is detailed above, even if the weather in the real world remains unusual. 

EXAMPLE SEASONS HERE