Especially for a campaign that features lots of outdoor adventuring and travel, keeping track of weather is one of the easiest ways to bring a touch of verisimilitude to your game. Even more fun (for me at last) is tracking the weather as it changes over time.
There’s nothing wrong with simply deciding what the weather’s like on key days in your game, especially if doing so has an intended effect on the story. Sometimes you want a showdown with cultist mercenaries to take place under the lightning-streaked skies of a brutal thunderstorm. But rolling randomly for weather can add a bit of randomness to outdoor encounters, even as it helps to make the world feel actively real to the characters and players alike.
Weather by the Numbers
Weather is obviously a regional and local phenomenon, meaning no single table can cover every sort of meteorological event you might need across multiple locations and environments. As such, start by defining generic categories of weather, ranging from perfect to bad through varying degrees of better, typical, and worse.
Keeping in mind the environment in which the party is adventuring, you can then assign specific instances of weather to each category. The sample table below covers three common fantasy adventure environments, which you can easily customize for your own campaign or use as models for other environments.
Weather patterns are relative to climate and seasons, so that precipitation might cover light or steady rain, torrential downpour, or snow depending on the locale and time of year.
Weather Over Time
If you want to determine the weather on key days in your campaign but have no need to track it as it changes, just roll to see what the dice turn up and summarize how the weather has shifted since the last time you rolled.
If you want to track how the weather changes over time, make note of the d8 roll on the first day. You then roll a d8 each new day (or every few days, as desired), but not to determine a new weather category. Rather, if the number you roll is higher than the previous roll, the category shifts up by 1 (to a maximum of 8). If the roll is lower, the weather shifts down by 1 (to a minimum of 1). If the number rolled is the same, the weather stays as it was.
Climate Controls
Over time, rolling on the table produces a pattern of shifting weather conditions that hover mainly in and around the “typical” middle, but which veer into perfect or bad weather with regular frequency.
If you want to change that frequency, you can adjust the pattern of the weather over time by adding a bonus of +1 or +2 to the d8 roll (still to a maximum of 8) or imposing a penalty of −1 or −2 (to a minimum of 1). Doing so pushes the weather toward perfect (with a bonus) or bad (with a penalty), letting you account for seasonal variation (wetter and stormier weather in the winter, drier weather in summer), the short-term effects of a nearby natural or magical disaster, and so forth.
Unusual Weather
To provide more variation, whenever you roll a 1 or an 8 on the die (before any adjustments), you can determine a chance for unusual weather. Unusual weather might inspire an isolated rainstorm in clear or overcast skies, a rare dry day in a rainforest jungle, a tornado in an area under the effect of cloud and storm, hail instead of rain as summer precipitation, and so forth. How often unusual weather occurs if a 1 or 8 or is rolled is left to your determination. It might be rare (a 1 in 10 chance) in a temperate inland nation, or might be common (a 1 in 4 chance) on an island or seacoast where sweeping winds can inspire sudden and dramatic changes. Or feel free to ignore the odds and invoke unusual weather whenever it suits the story.
Supernatural Weather
If your campaign is set in a high-magic realm, consider swapping in supernatural weather for any occurrence of unusual weather. The following examples work well for most fantasy campaigns, or can serve as inspiration for supernatural weather of your own. Rework the generic effects described here as appropriate for your game.
Alchemical Miasma: Rain or mist carries potent alchemical power that can deal damage, impose penalties on creatures caught in it, or induce weakness or illness.
Blood Rain: A haze of blood-red precipitation deals necrotic damage to any creature caught in it.
Creature Rain: A storm of arthropods or tiny animals might deal damage to anyone caught in it, and leaves its creatures to subsequently attack as swarms.
Dazing Haze: Rain, mist, or wind limits the actions or movement of creatures caught in it.
Eldritch Squall: Magic is temporarily made inert or amplified in chaotic ways (damage-dealing magic affects unintended targets, spells are reflected back at the caster, magical damage becomes a different damage type).
Elemental Precipitation: Mist, rain, hail, or snow shot through with elemental power might deal damage to creatures caught in it, or could deal extra damage to any creature who takes damage while exposed to the precipitation.
Grueling Storm: Creatures caught in the storm become temporarily physically or mentally impaired.
Illusion Zephyr: Swirling motes of light create pockets of mirage or illusion (creatures who aren’t there, altered landscape).
Necromantic Squall: A gray-black mist or haze causes recently dead creatures to randomly rise as undead.
Restorative Storm: Falling or drifting motes of light cause any restorative or healing magic to work at maximum effectiveness.
Seed Storm: Unusual seeds fall like rain, potentially dealing damage, limiting movement, or making it difficult to breathe. The seeds might then sprout into unnatural or magical plants.
Spectral Storm: Wind or precipitation manifests as spectral figures that might deal psychic damage or frighten creatures.
Telekinetic Gale: A gentle breeze can seize random objects or creatures and fling them about.
Wild Magic Storm: A miasma of eldritch energy disrupts spells and magic items (half damage, disadvantage on offensive rolls or advantage on defensive rolls).
Art by Dean Spencer