Mystara Wilderness Travel Calendar & Weather System (AC 1000)
Mystaran Calendar Overview
Mystara’s calendar consists of 12 months of 28 days each (336 days total), typically divided into 4 seasonsdatapacrat.com. The standard Thyatian naming of months (used in Karameikos and most Known World nations) is as followsdatapacrat.comdatapacrat.com:
Winter (early winter in the old year, mid/late winter in new year):
Kaldmont – “Early Winter” (28 days; contains Winter Solstice on Kaldmont 1)
Nuwmont – “Midwinter” (28 days; New Year’s Day on Nuwmont 1 in Thyatis, Karameikos, Darokin, etc.)
Vatermont – “Late Winter” (28 days)
Spring:
Thaumont – “Early Spring” (28 days; Spring Equinox on Thaumont 1. Alphatia, Rockhome, and some others celebrate New Year on this equinox)
Flaurmont – “Middle Spring” (28 days)
Yarthmont – “Late Spring” (28 days)
Summer:
Klarmont – “Early Summer” (28 days; Summer Solstice on Klarmont 1)
Felmont – “Midsummer” (28 days)
Fyrmont – “Late Summer” (28 days)
Autumn:
Ambyrmont – “Early Fall” (28 days; Autumn Equinox on Ambyrmont 1)
Sviftmont – “Middle Fall” (28 days)
Eirmont – “Late Fall” (28 days)
Each month has 4 weeks of 7 named days (Lunadain, Gromdain, Tserdain, etc.), though week designations aren’t usually numbereddatapacrat.com. The first day of the year is celebrated on Nuwmont 1 by most nations, though cultures like the Alphatians and Shadow Elves mark the new year at spring equinox (Thaumont 1), and Ethengar counts the new year in fall (their New Year’s Day on Sviftmont 6). This can impact trade calendars and when merchants consider their “fiscal” year – e.g. Alphatian ports might be closed or hold festivals at Thaumont 1, while Thyatian lands celebrate on Nuwmont 1.
Solstices & Equinoxes: The turning of each season is significant. Thaumont 1 (spring equinox) and Ambyrmont 1 (fall equinox) are days when day and night are equal length; Klarmont 1 is the longest day (summer solstice) and Kaldmont 1 the shortest day (winter solstice). Many cultures hold observances on these days. For example, on Klarmont 1 (Summer Solstice), Karameikans celebrate the Day of the Straw Men by burning straw effigies to ward off evil spirits during the year’s longest daylight. Likewise, on Kaldmont 1 (Winter Solstice) a tradition called Farewell to the Sun is observed in various Northern Reaches and Heldannic communities – bonfires are lit as this darkest day heralds winter’s heart. These practices can influence monster behavior: on Day of the Straw Men, the bonfire smoke and daytime revelry tend to keep creatures away from settlements that night. Conversely, the long darkness around Kaldmont 1 may embolden nocturnal monsters (e.g. undead or wolves) to roam earlier in the evening, though many communities counter this with all-night vigils.
Major Holidays & Effects: Throughout the year, different nations have festivals which can affect trade, travel, and even monster activity:
Nuwmont 1 – New Year’s Day: Marked as the start of the year in most human nations. It’s a day of feasting and rest. Trade caravans pause in major towns for celebrations, and road travel is minimal as communities hold fairs. In Darokin, Glantri, Karameikos and others, coming-of-age ceremonies take place now (youths of age 18 or 21 are recognized as adults). Monsters in winter hibernation are largely unaffected by the date, but human behavior (loud festivities, fireworks in some cultures) on Nuwmont 1 can keep opportunistic predators at bay that night.
Thaumont 1 – Spring Equinox: In nations like Alphatia and Rockhome, this is New Year’s Day (called the Day of Alphamir in Alphatian tradition). Day and night being equal symbolizes renewal. Many cultures celebrate planting festivals around this time. Shadow Elves honor “The Discovery of the Refuge of Stone” on this date with quiet reverence underground. Above ground, markets in human lands reopen for spring trade; caravans resume regular schedules after winter slow-downs. Wilderness encounters start to increase after equinox as many creatures emerge from winter dormancy – the first hunts of the season for predators begin as the weather warms.
Klarmont 1 – Summer Solstice: The longest day brings several festivals. In Karameikos, the Day of the Straw Men involves burning large straw dolls at dusk – a practice believed to scare off curses and malicious fey. The Ierendian Freedom Day and Crown Tourney also occur at this time, drawing crowds of spectators. The Soderfjord Jarldoms hold The Thing from Klarmont 1–7, a week-long gathering where laws are made and grievances aired under the midnight sun. During this period, trade in Soderfjord slows (as many farmers and leaders are at the Thing), but merchants take the opportunity to sell wares to assembled crowds. Monsters tend to avoid the large, armed gatherings (no intelligent raider would attack a full Thing meeting), but fey creatures are said to be active on Midsummer night – the Night of Fire on Klarmont 28 is a related event when Traladaran folk in Karameikos and Boldavian nobles in Glantri stay up to watch eerie red glows or “firefalls” in the sky. Common superstition holds that evil spirits are abroad on the Night of Fire; in game terms, a DM might increase the chance of an ominous omen or otherworldly encounter on that night. Adventurers traveling during these midsummer nights might witness strange lights or encounter wandering fey drawn by ancient solstice magic (e.g. will-o’-wisps near marshes or pixies playing pranks).
Ambyrmont 1 – Autumn Equinox: Day and night balance again. In the Alphatian Empire, this day is celebrated as Ancestors’ Day, a solemn holiday to honor the departed. Ethengar calls it the First Day of Hiding – a time when the nomads symbolically begin preparing for winter, bringing herds into sheltered valleys. As autumn begins, trading caravans accelerate to complete their routes before winter; you’ll see heavy wagon traffic on the Via Mare and other trade roads around this time. Monster activity often spikes in early fall – many creatures forage aggressively to fatten up before winter. DMs can foreshadow this by increasing minor encounters (e.g. more wolves stalking livestock as the wild game grows scarce toward late fall).
Sviftmont 8 – Vanya’s Day: In Thyatis and the Heldannic Territories, this day honors the Immortal Vanya (patron of conquest and courage). Military parades or war-games are common in Heldann. Travelers might find garrisons preoccupied with ceremonies, potentially leaving border roads less patrolled that day. Aggressive humanoids, if they have any instinct or lore about human habits, could exploit this; however, many such creatures also lie low due to the commotion of armed humans celebrating.
Eirmont 28 – Year’s End: The last day of the calendar is traditionally a time of accounting and indoor feasting. Before AC 1009, many cultures held quiet festivals of reflection or ancestor worship on Eirmont 28 or Kaldmont 28 (the very end of the year). Important Note: After the events of the Wrath of the Immortals (AC 1006–1009), the Day of Dread was established on Kaldmont 28 each year – a day when magic ceases to function worldwide. In a campaign starting in AC 1000, this phenomenon has NOT yet occurred, but the DM could foreshadow it via legends or strange magical fluctuations near year’s end. At the very least, on the last night of AC 1000, scholars note an uncanny stillness in the air – an omen of the dark times to come. In practical terms, AC 1000’s year-end should be treated normally (spells work, though many wizards and clerics might perform rituals to “thank” or appease the Immortals for the year’s magic). From AC 1009 onward, Kaldmont 28 becomes a fearful day when even magical creatures go to ground.
Summary of Behavioral Effects: Generally, winter months see minimal trade caravans (many passes snowed in; ships in northern waters winter in port). Monsters in cold climates hibernate or migrate; in temperate Karameikos, heavy snow is rare, but freezing rain and cold snaps in Vatermont can make travel perilous. During major holidays, human activity spikes in settlements (markets, festivals) but drops on the roads – meaning wilderness encounter frequency might dip slightly on those specific days (few travelers to prey upon), except near festival sites where opportunistic monsters might lurk on the fringes. Conversely, around equinoxes and solstices, there is a higher incidence of mystical occurrences. The veil between worlds is thin on those nights according to lore – a great opportunity for the DM to introduce “mood” events like ghostly processions, faerie lights, or unseasonable weather. For example, an Aurora might flash in the northern sky on the winter solstice even at latitudes that don’t normally see it – unnerving local animals. Or a sudden thunderstorm out-of-season might hit on the spring equinox as a sign of nature’s upheaval. These touches add immersion and can foreshadow coming challenges (e.g. an equinox storm could presage an Immortal’s displeasure or the approach of an otherworldly threat).
Finally, note that Mystara’s daylight hours vary by latitude. In Karameikos (~30°N) daylight lasts about 10.5 hours in mid-winter (roughly 6:40 AM to 5:00 PM) and about 14 hours at midsummer (5:00 AM to 6:55 PM). Farther north, the difference is more extreme: at 60°N (e.g. Norwold), winter sun may only be up ~6.5 hours (8:35 AM–3:05 PM) whereas in summer it stays light for over 18 hours. This means a winter journey in northern latitudes gives monsters a longer night to roam, while summer travels offer extended daylight (but also very short nights for full rest). The DM should consider twilight length as well – Mystara has about a 30-minute twilight at dawn and dusk. This can be important for scheduling watch shifts or determining when nocturnal creatures start stirring.
Daily Weather Tables: Eastern Karameikos (B10 Region)
The following tables provide day-by-day weather for a two-month overland journey in Eastern Karameikos, covering late spring (Yarthmont) and early summer (Klarmont) of AC 1000. This period spans 56 days (two Mystaran 28-day months, roughly equivalent to “60 days” of travel). The climate in Karameikos is moist temperate with mild winters and warm, stormy summersstockingthedungeon.blogspot.com. Old School Essentials (OSE) guidelines are used for temperature ranges and terminology, and each day’s entry includes:
Temperature: Approximate daytime high and nighttime low. (Karameikos spring highs range ~60–75 °F, summer highs ~80–90 °F, with cooler nights). “Cool” indicates unseasonably chilly day; “Hot” indicates a sweltering day for the season.
Precipitation: Any notable precipitation – clear, cloudy, rain, thunderstorms, etc.
Wind: General wind strength/direction – e.g. calm, gentle breeze, strong wind. (No tropical storms occur in inland Karameikos, but thunderstorms can bring brief high winds).
Notable Events: Special weather events or folklore for that day – e.g. festival effects, omens, or hazard warnings.
These tables not only help the DM track daily weather (for travel modifiers, visibility, etc.) but can be used as player-facing “wilderness forecast” handouts. For instance, if characters ask locals about upcoming weather (“Red skies this morning – think it’ll rain?”), the DM can convey a short-term forecast gleaned from these tables.
Yarthmont (Late Spring) – Eastern Karameikos Weather (AC 1000, Days 1–28) Format: Date — Temp — Precipitation — Wind — Notes
Yarthmont 1 (Lunadain) 🌡️ 65°F / 48°F (18°C / 9°C) — ☀️ Clear — 🌬 Light breeze from west Spring calm after previous rains; travel conditions good.
Yarthmont 2 🌡️ 66°F / 50°F — ☀️ Clear, few clouds — 🌬 Light breeze Dawn mist over rivers burns off by mid-morning. Spring planting begins.
Yarthmont 3 🌡️ 72°F / 51°F — ⛅ Partly Cloudy — 🌬 Moderate breeze from SW Increasing warmth; fluffy cumulus clouds. Forest paths drying.
Yarthmont 4 🌡️ 75°F / 53°F — ☁️ Overcast late — 🌬 Moderate breeze Humid afternoon. Animals more active before potential rain.
Yarthmont 5 🌡️ 60°F / 50°F — 🌧 Light Rain (morning) — 🌬 Gentle east wind Drizzly dawn, clears by noon. Roads slightly muddy.
Yarthmont 6 🌡️ 62°F / 47°F — 🌧 Showers likely — 🌬 Variable gentle wind Scattered rain. Trails puddled. Mushrooms abundant.
Yarthmont 7 🌡️ 68°F / 50°F — ⛅ Clearing (AM clouds) — 🌬 Light NW breeze PM Grey morning clears by midday. Fresh, rain-washed air.
Yarthmont 8 🌡️ 70°F / 50°F — ☀️ Clear — 🌬 Light NW breeze Sunny, full rivers. Excellent visibility.
Yarthmont 9 🌡️ 75°F / 54°F — ☀️ Clear — 🌬 Light breeze Beautiful spring day. Wildlife active near dusk.
Yarthmont 10 🌡️ 76°F / 55°F — ☀️ Clear — 🌬 Light breeze Drying trend. Dust rising. Normal travel speed.
Yarthmont 11 🌡️ 78°F / 56°F — ⛅ Partly Cloudy (PM) — 🌬 Moderate S breeze Afternoon clouds hint at future storms.
Yarthmont 12 🌡️ 82°F / 58°F — ⛅ Partly Cloudy — 🌬 Moderate S wind Unseasonably hot. Haze on horizon. Armored PCs tire faster.
Yarthmont 13 🌡️ 85°F / 60°F — ☁️ Humid, few clouds — 🌬 Gentle breeze Sultry weather. Animals need more water breaks.
Yarthmont 14 🌡️ 79°F / 59°F — ⛈ Thunderstorms late — 🌬 Gusty storm wind Evening storm (1–2 hrs rain, lightning). Take shelter.
Yarthmont 15 🌡️ 65°F / 55°F — 🌧 Rain before dawn, then cloudy — 🌬 Strong NW wind Pre-dawn squall clears. Overcast and cooler all day.
Yarthmont 16 🌡️ 70°F / 50°F — ☁️ Mostly Cloudy — 🌬 Moderate NW breeze Soggy ground. Brisk wind clears skies.
Yarthmont 17 🌡️ 72°F / 51°F — ☀️ Sunny — 🌬 Light wind Clear, pleasant. Wildflowers bloom.
Yarthmont 18 🌡️ 75°F / 53°F — ☀️ Sunny — 🌬 Light breeze Good visibility. Gentle weather.
Yarthmont 19 🌡️ 77°F / 55°F — ☀️ Sunny — 🌬 Light breeze Excellent travel day. Slight humidity near puddles.
Yarthmont 20 🌡️ 78°F / 56°F — ⛅ Partly Cloudy — 🌬 Light S breeze Hints of heat coming. No rain.
Yarthmont 21 🌡️ 85°F / 58°F — ⛅ Partly Cloudy — 🌬 Moderate S breeze Heatwave. Mirage ripples on road. Fatigue likely.
Yarthmont 22 🌡️ 86°F / 60°F — ⛅ Partly Cloudy — 🌬 Moderate SW breeze Hot, dry. Western clouds gather by dusk.
Yarthmont 23 🌡️ 80°F / 58°F — ☁️ Increasing clouds — 🌬 Light SW breeze Heavy air. Villagers expect rain.
Yarthmont 24 🌡️ 78°F / 57°F — 🌧 Showers (evening) — 🌬 Light variable wind Brief downpour post-sunset. Campers rig tents fast.
Yarthmont 25 🌡️ 74°F / 55°F — ☁️ Mostly Cloudy — 🌬 Gentle N breeze Cooler after overnight rain. Damp roads.
Yarthmont 26 🌡️ 72°F / 54°F — ☁️ Mostly Cloudy — 🌬 Gentle N breeze Sun pokes through occasionally. Cool for late spring.
Yarthmont 27 🌡️ 73°F / 54°F — ⛅ Partly Sunny — 🌬 Light NE breeze Farmers prep summer crops. Comfortable weather.
Yarthmont 28 🌡️ 75°F / 55°F — ☀️ Mostly Sunny — 🌬 Light NE breeze Last day of spring. Traladaran “Night of Fire” bonfires ignite across hills.
Weather Summary (Yarthmont): The late spring month starts cool and wet, transitions to a warm dry spell, and ends with a few rain showers and seasonable temperatures. Notably, around Yarthmont 12–13 an early heat wave hit (mid-80s °F) followed by thunderstorms on Yarthmont 14–15 breaking the heat. The latter part of Yarthmont saw generally warm, pleasant days with increasing hints of summer. By the end of the month, daytime highs regularly reach the upper 70s°F. This aligns with regional climate patterns – sunny, warming conditions in mid-late spring are typical for Karameikos, with occasional rain to keep the terrain lush. Adventurers would notice rivers running strong and flora in full spring growth. Travel conditions overall are good: mud was an issue only early in the month; later, dust became more of a nuisance on dry days.
Klarmont (Early Summer) – Eastern Karameikos Weather
Klarmont 1 (Summer Solstice) 🌡️ Warm 76°F / 56°F — ☁️ Scattered Showers — 🌬️ Light SE breeze turning gusty in rain Summer Solstice – morning is warm and partly sunny, but by afternoon scattered showers move in. Not a downpour, just intermittent light rain. Longest daylight of year; rain stops near sunset. Villages celebrate Day of the Straw Men: large bonfires tonight. The rain doesn’t dampen festivities – if anything, it creates steam clouds as bonfires roar. Adventurers near civilization might partake; in wilderness, monsters shy from settlements due to the flames.
Klarmont 2 🌡️ Seasonable 72°F / 55°F — ☁️ Overcast — 🌬️ Gentle NE breeze (cool) Grey skies, cooler than usual. Ground is damp from yesterday’s showers. A calm day of travel, if a bit gloomy.
Klarmont 3 🌡️ Seasonable 75°F / 54°F — 🌧️ Overcast, drizzle late — 🌬️ Gentle E breeze Notes: Another cloudy day. A fine drizzle begins near dusk, mostly in eastern hills. Visibility reduced in light fog over moors at night.
Klarmont 4 🌡️ Cool 68°F / 52°F — 🌧️ Steady Rain (morning) — 🌬️ Moderate N wind Rainy morning with several hours of steady rainfall. Trails become muddy. Afternoon sprinkles only.
Klarmont 5 🌡️ Cool 66°F / 50°F — 🌤️ Clearing by noon — 🌬️ Moderate N wind Clouds break by midday. Rainstorm aftermath leaves crisp, cool air. Waterskins refill from clean rain catch. Hungry monsters may emerge.
Klarmont 6 🌡️ Seasonable 72°F / 51°F — ☀️ Mostly Sunny — 🌬️ Light NW breeze Pleasant early summer day. Ground firms up. Good travel conditions.
Klarmont 7 🌡️ Warm 78°F / 55°F — ⛅ Partly Cloudy — 🌬️ Light W breeze Warmer with humidity. Woodsmen predict storms in a few days.
Klarmont 8 🌡️ Warm 80°F / 58°F — ⛅ Partly Cloudy — 🌬️ Light SW breeze (warm) Southerly breeze brings warmth. Heat lightning to south at midnight.
Klarmont 9 🌡️ Hot 88°F / 62°F — ☁️ Increasing Clouds — 🌬️ Moderate SW wind Hot, humid, and sweltering. Clouds thicken by sunset.
Klarmont 10 🌡️ Hot 90°F / 64°F — ⛈️ Thunderstorms (afternoon) — 🌬️ Gusty winds (storm) Strong afternoon thunderstorms. Rain, wind, lightning, risk for small boats.
Klarmont 11 🌡️ Seasonable 75°F / 60°F — ☀️ Mostly Sunny — 🌬️ Light W breeze Storm has passed – cleaner, cooler air. Minor flooding in low spots. Some trails require detours.
Klarmont 12 🌡️ Seasonable 74°F / 58°F — ☀️ Sunny — 🌬️ Light breeze Calm day. Shadow Elf lore marks this as “The Rejection,” but on the surface it’s uneventful.
Klarmont 13 🌡️ Seasonable 76°F / 59°F — ☀️ Sunny — 🌬️ Light breeze Idyllic summer day. Wildlife active. Foraging is excellent post-rain.
Klarmont 14 🌡️ Warm 80°F / 60°F — ☀️ Mostly Sunny — 🌬️ Gentle S breeze Warm and pleasant. Full moon with reddish hue seen in Glantri (“Night of the Red Moon”), but here it’s just atmospheric.
Klarmont 15 🌡️ Warm 81°F / 61°F — ☀️ Sunny — 🌬️ Gentle S breeze Clear and warm. Moonlight aids nighttime travel and patrols.
Klarmont 16 🌡️ Seasonable 78°F / 60°F — ☁️ Increasing Clouds (late) — 🌬️ Moderate SE breeze Fair morning turns grey by evening. Storm brewing to the southeast.
Klarmont 17 🌡️ Seasonable 75°F / 59°F — 🌧️ Rain Showers (morning) — 🌬️ Moderate SE wind Light morning showers, clearing by noon. Halflings commemorate this day in the Five Shires.
Klarmont 18 🌡️ Seasonable 77°F / 58°F — ⛅ Partly Cloudy — 🌬️ Light NE breeze (cool) Cooler breeze follows the rain. Travel is easy. Trails slightly soft.
Klarmont 19 🌡️ Warm 82°F / 60°F — ⛅ Partly Cloudy — 🌬️ Light N breeze Warming up again. In Five Shires, it’s “The Unsheathing,” but Karameikos observes nothing. Maybe a Hin NPC sharpens a blade in its honor.
Klarmont 20 🌡️ Warm 85°F / 62°F — 🌧️ Isolated Showers (p.m.) — 🌬️ Light NW breeze, shifting Very localized late-day rain in hills. Some hear thunder, others stay dry.
Klarmont 21 🌡️ Hot 88°F / 63°F — ⛅ Partly Sunny — 🌬️ Moderate W breeze Hot, high sun angle. Water consumption important. Sunburn risk rises.
Klarmont 22 🌡️ Warm 82°F / 61°F — ⛅ Partly Cloudy — 🌬️ Moderate W breeze Sea breeze cools the region slightly. Altan Tepes visible clearly.
Klarmont 23 🌡️ Seasonable 78°F / 60°F — ☁️ Mostly Cloudy — 🌬️ Gentle W wind Grey skies build in the evening. Humidity lower. Calm before possible weather shift.
Klarmont 24 🌡️ Seasonable 76°F / 59°F — ⛈️ Thunderstorm (early a.m.) — 🌬️ Gusty winds Pre-dawn storm hits hard, gone by morning. Day overcast and wet. Fallen limbs in forest paths.
Klarmont 25 🌡️ Seasonable 74°F / 58°F — ☁️ Mostly Cloudy — 🌬️ Light NW breeze Fog at dawn in valleys. Dry day but cool and overcast. Monsters less active.
Klarmont 26 🌡️ Seasonable 75°F / 58°F — 🌧️ Rain Showers (midday) — 🌬️ Light variable wind Short midday shower dampens roads. Mushrooms flourish again.
Klarmont 27 🌡️ Cool 70°F / 56°F — 🌤️ Clearing (p.m.) — 🌬️ Moderate N breeze Oddly cool. Clear skies return late. Evening travelers may need cloaks.
Klarmont 28 🌡️ Seasonable 75°F / 57°F — 🌤️ Mostly Sunny — 🌬️ Light N breeze Night of Fire (Traladaran tradition) — final day of the month is calm and clear. Bonfires and omens. Perhaps the PCs see a falling star or an eerie light…
Weather Summary (Klarmont): Early summer in Karameikos proved variable – frequent rain showers and a few thunderstorms interspersed with hot, sunny spells. Notable patterns include a cool, rainy spell around Klarmont 4–5 (with steady rain), a heat wave on Klarmont 9–10 followed by severe storms (temperatures hit 90 °F then dramatic thunderstorms on the 10th), and another series of showers and storms around Klarmont 17 and 24–26 (several days of on/off rain). Despite being summer, Karameikos saw some unseasonably cool days (highs only ~70 °F on Kl.27) as northern winds brought relief after storms. This reflects the continental climate influence – while summers are warm, rainstorms and front systems can cause swings in temperature. Travel impact: Mud was an on-and-off issue in Klarmont; adventurers likely had to slog through muddy roads after each significant rain. However, thanks to regular rains, water sources were plentiful (rain-filled streams, ponds). There were a few days of potential exhaustion risk due to heat (Kl.9–10 and Kl.21) – the DM could ask for Constitution checks or enforce OSE’s forced march rules if the party pushed hard on those very hot days without rest. On storm days (Kl.10, Kl.24), travel might be delayed or dangerous for a few hours. Overall, early summer weather gave a good mix of challenges (heat, storms) and easy days. By Klarmont’s end, the climate is fully in summer mode, setting the stage for the even hotter Fyrmont month ahead.
Using the Tables: A DM can use these tables actively (“On the morning of Flaurmont 14, you awaken to distant thunder…”) or as a reference to answer player questions (“Has it been raining lately? Is the road flooded?”). The Notable Events column also ties in in-world lore (e.g. solstice celebrations), which can enrich the campaign narrative and foreshadow cultural moments. For example, if the PCs are traveling on Klarmont 28 and camp near a Traladaran village, they might witness townsfolk gathered under the stars telling the legend of the Night of Fire – an excellent roleplay hook or simply atmospheric detail.
Note: These specific daily results were inspired by the Poor Wizard’s Almanac forecasts for the year (adjusted to AC 1000 conditions). If the DM needs to generate new weather on the fly, they can roll 2d6 each day to vary temperature (2 = much colder than average, 12 = much hotter), and another 2d6 for precipitation (with results like 2 = heavy storm, 12 = drought clear day, and middle values = light rain or clouds). The trends given here ensure consistency – for instance, after a day of thunderstorms, it makes sense the next day is cooler and clearer. DMs are encouraged to maintain a logical flow (fronts moving through, etc.) when improvising beyond the provided 60-day period.
Seasonal Weather Summaries by Region
As the campaign moves beyond Karameikos, the party will traverse various climate regions in the Known World – from arid deserts to open seas to highlands and sub-arctic realms. The following summaries provide an overview of typical seasonal weather for these regions, along with any special weather-related mechanics or hazards. All mechanics align with classic B/X or OSE assumptions (e.g. movement rates, rest rules, foraging, and the presence of standard wilderness encounter checks).
Desert Regions (X4/X5 – Great Waste and Alasiyan Desert)
Climate Overview: Mystara’s arid regions include the Alasiyan Desert of Ylaruam and the Great Waste on the Sindh–Hule border (featured in Master of the Desert Nomads and Temple of Death). These areas are characterized by extreme daytime heat, cold nights, and very low precipitation. The Emirates of Ylaruam in particular have a unique microclimate largely uninfluenced by surrounding weather – hot and dry year-round, with rain being very infrequent. The Great Waste (Sind Desert) is similarly parched but does experience a summer monsoon in certain locales (particularly the Asanda River Valley and adjacent plains).
Winter (Kaldmont–Vatermont): Desert winters are mild during the day and cold at night. Highs might reach 60–70 °F (15–21 °C) on sunny afternoons, but clear nights plunge to near freezing. Little to no rain falls in winter – the air is dry and often windy. In the Great Waste, a rare winter rain might occur once or twice (perhaps brief showers in Vatermont) but it’s not reliable. The Alasiyan basin essentially sees no rain at all in winter. Skies are usually clear. Behavior: Nomadic tribes keep close to winter oases or migrate to slightly warmer lowlands. Trade caravans still cross the deserts in winter (the cooler temperatures make daytime travel safer). However, nights are bitter cold – without shelter or fire, characters may need to make saving throws to avoid hypothermia if unprepared. Monsters: Many desert creatures are actually more active in winter since the daytime heat is not lethal – for example, giant scorpions or lizards might be seen at midday in January (Nuwmont) warming on rocks, something they wouldn’t do in peak summer. Mechanics: No special movement penalties in winter beyond the normal desert terrain slow pace (deserts count as Broken terrain in B/X, reducing travel to 2/3 normal). If a rare sandstorm blows in winter, it’s usually a “cold wind” storm off the mountains, possibly carrying freezing winds but little sand (more on sandstorms below).
Spring (Thaumont–Flaurmont): Spring in the desert starts pleasant – cool mornings warming to moderate days (70–85 °F, ~20–29 °C). By late spring, temperatures rise rapidly. Rain remains scarce; however, in some years a few spring thunderstorms may skirt the desert’s edges (especially near mountains or plateaus). These can cause brief downpours that create flash floods in arroyos and then evaporate. Generally, though, dry conditions persist. Winds in spring can be strong – this is the season of dust storms and sand-laden winds as the desert heats unevenly. (In the Sind region, hot winds blowing from the Great Waste are called the “Sirocco”, capable of reducing visibility and carrying fine sand.) Behavior: By mid-spring, wise travelers adopt hot-weather routines: traveling at dawn and dusk and resting during the blazing midday. Nomads move to their summer grazing grounds near dependable water. Monsters: Many desert creatures bear young in spring before the worst heat – meaning more sightings of juveniles or increased aggressiveness from parents. For example, a giant cougar might be hunting more desperately to feed its litter. Mechanics: Starting in later spring (Flaurmont/Yarthmont), enforce heat rules on especially hot days. In OSE/BX terms, if characters travel during the hottest part of the day (roughly 11 AM–4 PM) in extreme heat, have them Save vs Death (or Constitution check) or suffer fatigue/exhaustion or minor heat damage. In X4 it is suggested that those failing such a save take 1d4 points of damage from heat exposure (and even those who save might take a minimal 1–4 points). This represents heat exhaustion and sunstroke. Make sure to track water consumption – by late spring, a person needs at least 1 gallon of water per day in the desert (more if marching in armor). OSE notes that a day without adequate water can impose attack and movement penalties, require extra rest, or even cause damage. DMs should warn players that spring is turning to summer – if they don’t adjust travel hours and hydration, they’ll start suffering these effects.
Summer (Flaurmont’s end–Fyrmont): Summers are deadly hot. Daytime highs commonly exceed 100 °F (38 °C) and can reach 110–120 °F (43–49 °C) at midday in the deep desert. The air shimmers with heat; mirages appear almost daily on the horizon. Nights, by contrast, may drop to 70 °F (21 °C) or lower – providing some relief but also risk of exposure if one only has daytime attire. In Ylaruam, summer is bone-dry – virtually no rain falls for the entire season (the sky is a brassy, cloudless dome for weeks on end). In the Sind Desert/Great Waste, monsoon patterns reach the fringes of the desert in mid-to-late summer: In Felmont and early Fyrmont, humid air and thunderstorms push up the Asanda River Valley and plains. These storms are infrequent but intense – sudden downpours or even wall storms that can create flash floods in the waste. They are usually localized near the valley; much of the open waste beyond sees only dust. However, one or two severe monsoon storms might sweep across a wide area, causing a brief desert bloom. PWA forecasts for AC 1012, for example, note severe monsoon rains and flooding in late Felmont and even an “unseasonable” monsoon lasting into Sviftmont one year – these are exceptional cases. Typically by Fyrmont (high summer), any rains recede and the desert returns to dry, with slightly shorter days by late summer. Behavior: Almost all intelligent desert denizens become nocturnal in summer. Travel is done at night by both nomads and caravans. Midday in the open is suicide – even lizards seek shade. Adventurers crossing a summer desert must adapt: they should schedule rests at midday (and per OSE, characters must rest 1 day in 6 of travel regardless; in summer desert, that rest might need to be in shade or risk collapse). Monsters: Some monsters estivate (summer hibernation) during the peak heat – e.g. certain giant lizards or insects may burrow and wait out the hottest weeks. Others become active only at night: expect a spike in nocturnal encounters (giant bats, jackalweres, desert ghosts, etc.). Additionally, the rare summer storms can awaken dormant threats: a sudden rain might cause giant scorpions to emerge from cracks in the ground or wash out nests of burrowing monsters. Summer is also sandstorm season (see Hazards below). Mechanics: In summer, daily heat checks are critical. If PCs insist on traveling under the noon sun, require Saves vs Death each hour (or each hex) of midday travel. Failure = exhaustion or damage (1d6 per hour exposed, for example). Armor or heavy clothing imposes penalties (possibly automatic failure after a short time). Enforce water use: each PC might need 2 gallons per day in extreme heat. Without magical aid (e.g. create water), they’ll need to carry substantial supplies or locate oases. Foraging in true desert is nearly impossible except after a rare rain (default assume no reliable foraging unless near an oasis or the desert’s edge). If using OSE’s foraging rules: in Barren desert, treat chance as minimal (perhaps 1-in-6 for scant succulents or a small game, if that). The Great Waste’s summer monsoons present a double-edged sword: they provide water but also create hazards like floods, sinkholes in suddenly wet sand, and attract predators to new waterholes. Flooded wadis can sweep away travelers – DMs can spring a flash flood encounter where PCs must scramble to high ground or take 2d6 bludgeoning from a torrent.
Autumn (Ambyrmont–Eirmont): Early autumn remains very hot in the day, though each week brings slightly shorter periods of sun. By Ambyrmont (late summer/early fall), the intense heat starts to ease off to merely hot (90s °F). This is a dusty season – after the monsoon or summer dryness, vegetation is sparse and ground is cracked. Occasional dust storms kick up in the afternoons, especially in Ambyrmont when the land is at its driest and winds shift. These are not as fierce as peak summer sandstorms, but they can still reduce visibility and coat everything in fine sand. By Sviftmont (mid-fall), nights grow significantly cooler (down to 50 °F/10 °C or lower by late fall), and days, while warm (80s °F), are far more bearable. There is a slight chance of autumn rains – sometimes a last gasp of the monsoon might drift in during early Ambyrmont (as happened unseasonably in AC 1012, when monsoon rains lingered into Ambyrmont causing flooding south of the Atruaghin Plateau). Generally, though, fall is dry until winter. Behavior: This is the traditional season for long caravan crossings. The great trade route between Selenica and Ylaruam, or Sind to Jaibul, often schedules departures in early fall so that the journey happens in cooler weather (and hopefully ends before winter storms in the mountains). Nomads have another mini-migration in fall, moving from deep desert summer havens to more sheltered winter grounds. Monsters: Activity picks up as the weather moderates. Many desert predators that lay low in summer come out to hunt more often in fall to build fat for winter. Adventurers might see an uptick in encounters around oasis regions as creatures big and small converge on remaining water sources (which begin to shrink in fall). An interesting phenomenon in the Great Waste: mirages are still common in the early fall heat, and can sometimes conceal actual threats. For instance, at a distance the shimmering air might hide the true number of nomad riders approaching (appearing as a wavering single silhouette), or an oasis might appear closer or farther than it is, leading a thirsty party off-course. Mechanics: Temperatures in early fall can still warrant midday heat checks (especially Ambyrmont). By late fall (Eirmont), that’s no longer necessary. Sandstorms remain a threat until about Ambyrmont; by late fall, larger regional windstorms die down. The DM can simulate an occasional sandstorm event in summer or early autumn: e.g. once every 1d10 days during peak summer, and maybe 1d20 in early autumn. See Desert Hazards below for sandstorm mechanics. In fall, navigation is easier – the skies are often clear, and one can orient by stars or sun. OSE’s default chance to get lost in deserts (2-in-6 without a guide) may be lowered to 1-in-6 in calm, clear fall weather, but note that mirages or featureless terrain can still mislead travelers even under clear skies. DMs might give a bonus to Navigation checks in autumn due to calmer conditions.
Key Desert Hazards & Mechanics:
Heat Exhaustion and Sunstroke: As noted, in extreme heat conditions (especially summer midday), characters must take precautions. A simple rule: during any hour (or 5-mile travel segment) of >100°F heat exposure, each character must Save vs Death (or make a Con check). Failure means they suffer one level of exhaustion (in 5E terms) or -2 penalty on attack rolls and movement rate halved until they can rest in cooler conditions. If using B/X damage approach, failure could instead deal 1d4 or 1d6 hit points of non-lethal damage (representing heat prostration). In X4, even successful saves still resulted in minor damage; you can optionally have a success cause the character to lose 1 hp (or no damage if they had protective gear or plenty of water). Encourage players to avoid this by traveling at night or twilight. Provide in-world warnings (“The guide insists you all take shelter through noon, as the rocks themselves are too hot to touch.”). If players persist in noon marches, track their water closely – consuming water can grant advantage on the save or negate damage for that hour.
Dehydration: OSE mentions penalties after a day without water; in the desert, those penalties should kick in faster. Rule of thumb: a character needs ~1 gallon (4 liters) per day of water in moderate heat, and 2+ gallons in extreme heat. If a character has less than half the required water in a day, they must Save vs Poison at day’s end or suffer dehydration (a level of exhaustion or -2 attack/move as above). No water at all automatically causes dehydration (no save). After two days of dehydration, a character cannot recover hit points and is dangerously close to death. The third day with insufficient water should prompt a Save vs Death to avoid collapsing (0 hp). These are harsh rules, but Mystara’s deserts are unforgiving – Poor Wizard’s Almanac notes that the Alasiyan Basin is almost entirely dry and any rain evaporates quickly, so water is life. Smart parties will carry ample water or use magic; others may need to spend actions during encounters to search for shade or water (e.g. using a divining rod or following an animal to water at dusk).
Sandstorms: Fierce sandstorms (also called “khamsin” or “simoon” depending on local tongue) are one of the deadliest hazards in the open desert. These storms usually occur in summer afternoons or early evenings when hot air and cooler air masses collide. Occurrence: The DM can check for sandstorms during summer and early fall. For example, a 1-in-6 chance each day in Fyrmont, 1-in-8 in Felmont and Ambyrmont, only 1-in-20 in other months (if at all). Alternatively, tie it to an encounter roll: on an “encounter” that turns up no creature, consider a sandstorm as an environmental encounter. Effects: When a sandstorm hits, describe a wall of dust on the horizon growing and then engulfing the area. It will drastically reduce visibility – to virtually zero (you can see only a few feet). Travel becomes impossible; anyone separated from the group may get lost (treat as automatic lost direction if moving during storm). The sand’s blast is painful: all characters and creatures caught in the open must make a Save vs Breath Weapon (or Dex check) to properly cover up. Those who fail suffer abrasions and choking – assign a small amount of damage (e.g. 1d3 or 1d4) and possibly blindness for 1d6 hours after (sand in the eyes). Even those who save will be coughing and have gritty skin (no damage). Tents or tarps can provide shelter if secured – otherwise the storm can tear flimsy shelters away. A strong sandstorm can last 1d4 hours (or more for truly massive ones). Mounts and pack animals may panic; handlers need to succeed an Animal Handling or morale check for their beasts or risk them bolting. After the storm, the landscape may be subtly altered – dunes shifted, tracks erased. Characters without a guide may need to reorient themselves (forced Navigation check or they end up off course). For added challenge, DMs can require the party to dig out any mostly buried gear or mounts (there’s a chance things get buried in sand). On the positive side, a sandstorm can also cover the party’s tracks effectively and deter pursuers.
Dust Devils & Mirage Effects: Not every desert weather event is a full sandstorm. Smaller dust devils – swirling dust whirlwinds – might be encountered on hot afternoons. These usually last a few minutes, dancing across the flats. They are mostly harmless (perhaps startling mounts or coating gear with sand), but folklore might attribute them to air spirits. Mirages are very common on hot days, especially in summer. A mirage might make a distant dune look like a shimmering lake or cause travelers to see false cliffs or buildings at the edge of vision. DMs can use mirages to introduce uncertainty: for instance, the party might “see” a gleaming city on the horizon at midday – if they investigate, by evening they find only sand. This can be a good roleplaying challenge (wasting time and resources chasing illusions). Random Encounter Layering: A clever trick is to combine mirages with encounters. Example: as the party crests a dune, they see what looks like a lake with palm trees (mirage)… also, some shapes moving near it (could be an actual band of gnolls or could be mirage reflections). Perhaps the oasis is real but the water is a mirage covering quicksand, etc. Or a bandit ambush could use a mirage spell to lure the party toward a trap. In game terms, if a random encounter is indicated during high noon, you might decide the encounter is illusory – e.g. “You spot what appears to be a caravan in the distance, but it never seems to get closer,” hinting it’s a mirage. Conversely, you could hide a real encounter behind a mirage: e.g. giant lizards lying in wait beyond a heat-haze who aren’t noticed until they are much closer than anticipated. Encourage players to make Wisdom checks to discern reality, or allow characters from desert regions to be less fooled by common mirages.
Foraging and Survival: Desert foraging follows classic B/X rules – in true desert, forage yields are scant. Players should not expect to hunt game easily (at most, a small lizard or a desert hare once in a while). OSE suggests some terrain just can’t support foraging; the Alasiyan deserts definitely qualify. An oasis or the Ust-Urt Savannah on the fringe of Ylaruam might allow some hunting (small antelopes, edible roots) with DM discretion. Otherwise, parties must carry provisions or rely on magic. Orientation is also a challenge – the flat, featureless wastes require Navigation proficiency or lots of survival skill. The PWA notes that the grasslands of Ust-Urt have weather akin to the steppes, meaning if the party sticks to the very edge of the desert they might get more rain and food (but likely more encounters with settled or patrolled areas). DMs can subtly push lost characters toward the nearest water by having wildlife tracks or birds appear more frequently in the direction of water.
Overall, adventuring in desert regions should feel markedly different: harsh and majestic. The weather itself is a primary antagonist. As the party crosses the Great Waste, describe the relentless sun, the way everything (from armor to water flasks) gets coated in fine sand, how each evening they shake out their bedrolls and a cup of sand falls out. Emphasize wide daily temperature swings – perhaps a magic sword left out at noon becomes too hot to hold, or a character’s breath is visible in the chill pre-dawn hours. Use weather to wear them down: a sandstorm separates the party members, or an unexpected monsoon flood forces them to higher ground where a hostile nomad band waits (layering weather and encounters for drama). By incorporating these elements, the journey through X4 and X5’s desert becomes as memorable as any battle – truly driving home the theme of survival against the elements.
Sea Voyages (X1/X6 – Sea of Dread and Sea Travel)
Once the party embarks on ocean journeys (such as traveling to The Isle of Dread in module X1, or the voyages in X6 Quagmire!), they will encounter the dynamic and sometimes perilous Sea of Dread and surrounding waters. Mystara’s seas have their own weather patterns, and the sea conditions (wind, waves, visibility) greatly impact travel speed, navigation, and safety. Below is a seasonal overview for sea routes likely taken in the Known World’s tropics and subtropics, followed by specific mechanics for sailing conditions.
Geography & Climate Context: The Sea of Dread lies south of Karameikos, Thyatis, and the Five Shires, dotted with islands (Minrothad, Ierendi, and farther out, the Thanegioth Archipelago where the Isle of Dread is located). The southern part of this sea is tropical (closer to the equator), while the portion nearer the continent is more subtropical/temperate, moderated by warm currentsstockingthedungeon.blogspot.com. Generally, weather systems move west to east across this part of the worldstockingthedungeon.blogspot.com – meaning storms that hit the Minrothad Isles often travel onward toward Thyatis or the eastern sea. The prevailing winds in the summer tend to be gentle trade winds from the east or southeast (helpful for ships sailing westward), whereas winter can bring northerly winds and gales in the temperate zones.
Winter (Kaldmont–Vatermont): Winters in the Sea of Dread (roughly corresponding to our December–February) are relatively mild, especially in the southern reaches. Near the equator (Thanegioth islands), there is no true winter – it remains warm (around 80 °F/27 °C) year-round, and the concept of seasons is defined more by wet vs. dry periods. In the northern part (near Thyatis/Minrothad at ~30°N latitude), winter brings cooler temperatures (60s °F, ~15–20 °C sea surface) and more frequent storms on the temperate fringe. The northern coastal waters can see winter gales – strong winds and big waves generated by cold fronts moving off the continent. However, snow or frigid conditions are virtually unknown at sea level here (even in Kaldmont, sea spray might be chilly at night but not freezing). Rainfall in winter is moderate: the southern tropical zone actually has a dry season roughly in winter (less frequent rain in Nuwmont/Vatermont), whereas the Thyatian coastal areas get more winter rain from passing fronts (Mediterranean-style rainy winter)stockingthedungeon.blogspot.com. Sea State: In winter, the visibility is often excellent on clear days (low humidity, crisp air), allowing lookouts to spot land or sails up to the horizon ~24 miles. But when storms roll through, visibility can drop with rain and mist. Waves: In the open Sea of Dread, winter storms can kick up large swells (10–15 ft waves) that persist even after the weather clears. Ships will pitch and roll – those without seafaring experience (PCs included) might need to save vs Poison or make Con checks to avoid seasickness in rough winter seas. Winds: OSE provides a simple sailing wind table – in winter there’s a higher chance of strong winds or gales. Mariners consider Kaldmont a dangerous sailing time near the coast due to sudden gales (2d6 roll of 12 indicating a gale). Farther south, winter winds are gentler. Many captains in Minrothad dry-dock their smaller vessels during the worst winter month, sending only larger ships on long voyages. Travel: Despite storms, winter can be a good time to sail from the northern hemisphere toward the equator (e.g. from Thyatis down to Ierendi) because the wind patterns might push south. However, returning northward might be slower. The X1 journey to Isle of Dread could certainly be undertaken in winter, but the DM could introduce a dramatic storm at sea to test the party’s mettle – e.g. a New Year’s gale in Nuwmont. According to OSE’s sailing rules, a gale triples ship speed but is hazardous; we’ll cover mechanics shortly, but basically winter = higher risk of such conditions.
Spring (Thaumont–Flaurmont): In spring, the weather in the Sea of Dread begins transitioning. For the northern parts, spring brings fewer cold fronts – by Flaurmont the heavy winter storms abate. Rain shifts: the Thyatian and Minrothad region sees a drier late spring (similar to Earth’s Mediterranean spring where rains decrease). The tropics (Thanegioth) start moving toward their wet season as summer approaches – early spring is still relatively dry, but by late spring/early summer, the frequency of tropical showers and thunderstorms increases. Winds in spring can be variable: calm days become more common as the winter pressure systems break down. Sailors might find themselves becalmed on some days (little to no wind – a result of transitional weather, perhaps a 2 on the 2d6 wind roll for “No Wind”). Conversely, spring can also have surprise squalls – short-lived but intense storms, especially near the equator where warm water fuels convection. Sea State: Generally moderate in spring – not as rough as winter, but some lingering swell early on. By late spring, the sea is often quite calm except during squalls. Visibility is usually good, though increasing humidity can cause morning sea fog or haze along coasts in Thaumont and Flaurmont. Travel & Encounters: This is a favored time for setting sail on long voyages. Many merchant ships depart in Yarthmont for places like Sind or Davania to take advantage of expected calmer seas before hurricane season. Adventurers at sea in spring might encounter more fog banks (especially in the mornings) – which can serve as natural ambush cover for pirates or sea monsters. The DM can describe eerie calm dawns where the sea is flat as glass, and the only sound is the creak of the ship – a different kind of tension from roaring storms. During such calms, navigation by sail is slow (the ship might only drift at 1/3 normal speed unless rowed). The crew might break out oars or just wait for wind. Encounters: becalmed ships can become targets for predators from the deep (e.g. a giant octopus might think a stationary ship is a curious object to investigate). As spring progresses, sea life becomes more abundant – warmer waters bring fish and whales northward. This might mean a better chance of non-threatening encounters like a pod of dolphins (a good omen to Mystaran sailors), or conversely, the appearance of a whale could draw a hunter like a kraken or sea serpent into the area.
Summer (Felmont–Fyrmont): Summer is sailing season in the tropics – but it’s also storm season. In the Sea of Dread and the tropics, the height of summer (Fyrmont, the late summer month) typically corresponds to the hurricane/typhoon season. During Felmont (midsummer) and especially into Fyrmont and Ambyrmont (late summer/early fall), powerful tropical cyclones can form over the warm ocean. These are rare but devastating events – essentially giant storms (gales and storms on the OSE wind table) with winds 60+ mph, massive waves, and torrential rain. PWA weather records note things like “severe coastal storm south of the Atruaghin Plateau likely” in late summer – evidence of such tropical storms. Not every voyage will hit a hurricane, but the risk is there in high summer, especially if traveling long distances (the DM might roll a random event for a storm if journeying across weeks at sea). Aside from cyclones, regular summer weather is generally hot, humid, and with daily squalls in the tropics. Near the equator, expect near-daily afternoon thunderstorms or showers during the “rainy season” (Felmont through Fyrmont is noted as the three-month rainy season in some tropical regions). These are usually short (an hour or two) but can be intense. Skies are often partly cloudy with brilliant sun in between rains. In the more temperate parts of the sea (near Ierendi/Minrothad), summer is actually relatively dry and calm except when a stray storm passes. Temperatures are warm to hot – on deck under the sun it can feel over 90 °F (32 °C) easily, so crews often rig awnings or work shirtless. Winds: Summer typically has consistent trade winds blowing from east to west or southeast to northwest in this region. That means a ship heading west (toward the Isle of Dread from Thyatis direction) has a steady tailwind – good sailing. A ship returning eastward may need to tack or take a slower route using known currents. However, when a storm system approaches, winds can shift rapidly. OSE’s optional wind table suggests a good chance of fresh breeze (normal) or strong breeze (+1/3 speed) on most summer days, with occasional high winds or near gale if a storm front is near. Sea State: For much of summer, seas are moderate – waves of 3–6 feet with whitecaps in normal winds, which is manageable for most ships. During thunderstorms, localized rough patches occur but pass quickly. The real danger is a tropical storm or hurricane: waves can exceed 20–30 feet, and the sea surface becomes chaotic. If the party is caught in such a storm, it might become a set-piece event (see Mechanics below for how to handle). Navigation: Summer haze can sometimes reduce visibility a bit (especially in humid doldrums). But on clear days, one can still see a long way. Spotting land might be trickier in heavy haze until closer (maybe 18 miles instead of 24). Encounters: Summer brings rich marine life – schools of flying fish, sharks trailing ships, maybe even colossal creatures basking in warm waters. There’s also more ship traffic; many merchants and pirates sail in summer due to favorable winds. The Voyage of the Princess Ark journals mention encountering everything from waterspouts to sea monsters in tropical waters – the DM can incorporate things like a sudden waterspout (tornado over water) during a squall to add excitement, or an encounter with the “Sea Hermes” (sea elves or tritons) who are more active in warm months. Monsters: consider that sea dragons or marine hydras might venture nearer to shipping lanes in calmer weather to hunt prey, whereas in storms most creatures dive deep for safety.
Autumn (Ambyrmont–Sviftmont): Early autumn is actually an extension of late summer patterns at sea. Ambyrmont (late summer/early fall) is often still part of the hurricane season. In fact, some of the worst tropical cyclones historically strike in early fall. By Sviftmont (mid-fall), the tropical rainy season starts to wane. The weather begins to stabilize with fewer daily thunderstorms; however, the interplay of cooling air and warm ocean can spawn fog in some areas (especially around cooler currents or autumn nights). The northern parts of the sea begin getting more frequent temperate storms again as the year nears winter (though those really ramp up in late fall into winter). Winds: In autumn, winds gradually start shifting. Those steady summer trades can become less reliable by late fall. Storm winds in autumn can be tricky – occasionally, a dying hurricane might curve north and hit areas like Ierendi or even the southern coast of Darokin as a gale or tropical storm. So one might get a period of eerie calm (the “eye” or after a storm) followed by very gusty days. Mariners in the Known World know that by late Ambyrmont, it’s wise to be heading to safe harbor. Sea State: Early fall seas can be rough if a cyclone hits, otherwise moderate. By mid-fall, seas are mixed – calmer in tropics as monsoon/hurricane season ends, but starting to become more restless in higher latitudes as autumn cold fronts stir up swells. If the party sails back from Isle of Dread around this time, they might notice bigger swells as they approach the continent in Sviftmont, indicating changing seasons. Visibility: Autumntime often has haze on the horizon due to still-warm water and cooling air. This can slightly shorten how far away something can be spotted. Also, daylight shortens, so there’s more dusk and dawn sailing under low light. Autumn sunsets at sea are spectacular but also remind the crew that nights are growing longer (good for stealth, bad for visibility). Encounters: Many captains try to conclude their voyages by late fall to avoid winter gales, so by Sviftmont the sea-lanes might be a bit quieter (except for adventurous or urgent missions – like the PCs!). Piracy might spike just before the “off-season” – pirates making one last score before hiding out for winter. Sea creatures might also have seasonal patterns: e.g. migratory whales head to warmer waters in fall (so near the end of the year you might see more whales passing Ierendi going south). Predators follow them, so maybe a party sees a whale being attacked by a giant squid on their route. As weather cools towards winter, giant aquatic monsters could become more lethargic (depending on if they’re cold-blooded). But intelligent ocean races (tritons, merrow, etc.) could take advantage of fewer humans sailing to extend their territories.
Sea Travel Mechanics & Hazards: When running the oversea portions of X1, X6, or any module where the party takes a ship, it’s important to simulate wind and waves without bogging down. OSE/BX provides a straightforward framework:
Wind Conditions: Each day (or each 8-hour sailing watch), the DM can roll for wind using a 2d6 table (as given in Champions of Mystara and OSE optional rules):
2 = No Wind – the ship is becalmed. If the vessel has oars (galley or longship), it can row at 1/3 normal speed (rowing is tiring, so crews can’t sustain it 24 hours). Otherwise, you drift. This result is more common in late spring or certain calm zones (like the doldrums around the equator).
3 = Faint Breeze – sails give only 1/3 normal speed. Sea is smooth with slight ripples. Good for fishing, bad for making haste.
4 = Gentle Breeze – about 1/2 normal speed. Enough to make headway, albeit slowly.
5 = Moderate Breeze – about 2/3 speed. Small waves, steady movement.
6–8 = Fresh Breeze – Normal sailing speed. This is the default assumed wind in travel calculations (e.g. a sailing ship with Move 120’ (40’) has ~24 miles/day in gentle to fresh breeze). Waves have whitecaps, ship moves well.
9 = Strong Breeze – about 4/3 (133%) normal speed. The wind is stiff; crew might reduce sail a bit to maintain control. Waves 6–8 feet. This is often the best wind for fast travel if the ship and crew are sturdy.
10 = High Wind – about 1.5× (150%) normal speed. Very strong wind; non-expert crews might start to worry. Rigging strain is considerable. Waves are becoming large (~10+ feet). If sustained, crew may need to shorten sail to avoid damage (GM could treat this as either still +50% speed with risk, or force the crew to effectively behave as “strong breeze” instead for safety).
11 = Near Gale – Speed doubled (200%), but danger is close. Winds howl. Waves 15+ feet, spray flying. At this point, small ships are in peril. There’s a chance of taking on water or minor damage. (In OSE, a near gale would likely trigger a check or minor hazard but not automatically wreck a seaworthy ship.) It might be wise to reef sails (reduce sail area) and run with the wind. If near land, ships must be very careful of being driven aground.
12 = Gale or Storm – Speed tripled if running with wind (effectively up to 300% speed), but ships are in severe danger. A true gale has winds of 40-60 mph; a storm (or hurricane/typhoon if tropical) can exceed 70+ mph. Waves can reach 20-30 feet or higher in a hurricane. Mechanics for storms: When a gale hits, every round (or hour of travel) the pilot must make a Ship Handling check (use the captain’s Wisdom or a proficiency, or simply a Luck roll) to avoid catastrophe. If the ship is seaworthy and not overburdened, it can attempt to run before the gale – basically letting the wind carry it in a somewhat controlled way. OSE suggests handling it like this: the ship is blown in a random direction at 3× normal speed (you can roll 1d6 for direction relative to intended course). If this random course would drive the vessel toward known land, there’s a 75% chance of wrecking on the shore – very dangerous! If the ship is unseaworthy (like a jury-rigged raft or a badly damaged ship), then in a full storm it has an 80% chance to simply founder (sink). Even a good ship might suffer damage: you can roll for something like a mast breakage, sail tear, or man overboard. Crew on deck must hold on or potentially be swept over (Dex checks or Save vs Death to grab rigging perhaps). Navigationally, a ship caught in a storm will likely be blown off-course significantly – after the storm, the party might need to re-chart their position (if they have no magical or expert navigation, they could be hundreds of miles from where they thought). Visibility in a gale is near zero – effectively night conditions even at noon, with rain and spray cutting sight to a few ship-lengths.
To simplify, you might not roll wind daily if you prefer a narrative approach – instead, decide that a certain leg of the journey has mostly fair winds (fresh breeze) with one period of calm and one big storm. However, using the table can add unpredictability that players must react to, which is fun.
Wave Height and Sea State: As indicated alongside wind categories, wave heights correlate with wind force. In calm or faint breeze, waves are negligible (only ripples). Moderate to fresh breeze: waves of a few feet, enough to cause pitching but not hazardous. Strong to high wind: large waves (6–12 feet) – the deck will be heaving, making tasks harder (maybe a -1 or -2 to delicate actions or missile fire). Near gale: very large waves (15–20 ft); it’s practically impossible to do anything on deck without being lashed to something. Visibility of other ships becomes intermittent as you dip between wave troughs. In a storm, waves become massive and chaotic – ships risk being broached by a wave (hit broadside) and rolling. Characters on a small craft could be washed overboard. If an overboard situation occurs, note that visibility to find a man in the water in stormy seas is slim (spotting distance maybe 40 yards or less in rain). For mechanical effect: In strong winds or higher, you could require Dexterity or Strength checks for PCs moving on deck to avoid slipping or being knocked down by a wave. Combat on a ship in gale conditions would be extremely difficult – possibly granting everyone cover (due to visibility) but also imposing disadvantage (5E) or -4 (B/X) on attacks due to the instability and chaos.
Visibility at Sea: Over water, the horizon distance depends on observer height. A lookout atop a mast can see perhaps 24 miles on a clear day (as given in PWA: land spotted at ~24 miles). For simplicity, assume clear weather visibility ~20-24 miles, enough to see big islands or mountains as a hazy outline, or the sails of a large ship as a tiny speck. However, any fog, rain, or mist drastically cuts this. In thick fog, one might not see beyond a few dozen yards (OSE notes ships may only be identified at 300 yards in clear conditions, and as little as 40 yards in dense fog). During heavy rain or squalls, visibility might be 1d4 × 100 yards at best – essentially the ship could stumble right into an island or another vessel. Night: At sea, without modern lights, night visibility is as far as starlight or moonlight allows – perhaps a mile or two for large silhouettes (e.g. seeing the loom of land or a black shape of a sail against starlit sky), but practically, unless there’s a lighthouse or a bright moon, it’s very limited. DMs should make liberal use of Perception checks or surprise rolls when ships meet at night or in fog.
Navigation & Getting Lost: OSE gives a base 2-in-6 chance to get lost at sea if no navigator, and even with a skilled navigator it’s possible in featureless ocean. Mist, storms, or currents can throw a ship off course. If using a hex map, you can secretly adjust their course if lost. Particularly after a storm (where they likely had to run with wind), the party might need to make an Int check or examine star positions to re-orient. You can reveal landfalls as surprises if they’ve gone off track (e.g. “After days at sea, land is sighted – but according to your chart, no land should be in that direction…” meaning they’re lost).
Sea Encounters & Effects of Weather: Some encounters are influenced by weather. For example, sea monsters often avoid rough weather by diving deep. Encounters with giant squid, sea serpents, etc., are more likely in calm or moderate seas. In a dead calm, the eerie stillness might be broken by a sea monster rising to inspect the becalmed ship. Conversely, undead pirates or raiders might choose a foggy morning or stormy twilight to strike, using weather as cover. Navigation hazards like reefs or shoals are harder to spot in rough water – after a storm, a reef might have shifted sand and become a new island or vanished shoal (Mystara’s seas are geologically active in some areas, particularly around the Thanegioth Archipelago volcanoes). A neat hazard from X1’s setting: sudden kelp beds or “sargasso sea” patches can entangle a ship’s rudder or slow progress – often these occur in warm, calm seas.
To summarize sea travel: good weather allows the ship to make full progress (24 miles/day for a typical sailing ship, more if wind is favorable). Bad weather (gales, storms) can either speed the ship along a random path or halt progress entirely while they heave to (drop sails and wait). A day of calm means little progress (perhaps only drifting a few miles with currents). The DM should narrate the voyage with attention to wind shifts (“By late afternoon the wind veers to the north, pushing you off your intended westward course a bit”), and encourage player decisions like adjusting sail, changing heading to find better winds (tacking), or even magical solutions (casting Control Wind or similar, if available, to fill the sails). The PWA note to mariners indicates local weather systems in one region can extend far out to sea, so planning routes with seasonal prevailing winds in mind is key – for example, an experienced NPC captain might say “We’ll take the southern current, it’s calmer this time of year even if it’s longer.”
Finally, ensure to play up the feel of sea weather: the oppressive stillness of a doldrums noon where the sea is like glass and everyone is sweating buckets; the exhilaration of a fresh breeze where the ship cuts through whitecaps and everyone’s spirits rise; the terror of a black storm front rising like a wall, with lightning forked across the sky, as the crew reefs sails and prays to Protius (Immortal of the sea). Weather at sea should be almost a character in itself – fickle, sometimes benevolent, sometimes wrathful. And remind players: unlike on land, they cannot simply seek shelter in a cave or under a big tree – they are exposed on the wide ocean, at the mercy of the elements and their own seamanship.
Sea Wind and Sailing Conditions (Use with Mystara maritime travel: X1, X6, Isle of Dread, and long sea voyages)
Wind Roll (2d6): 2 Wind Force & Direction: Calm – No notable wind Sailing Speed: 0 (Becalmed; oars only at 1/3 speed) Sea State: Flat, glassy sea Navigation/Visibility: Clear sky, excellent visibility (20+ mi). Night sky brilliant. Drifts with current.
Wind Roll (2d6): 3 Wind Force & Direction: Faint Breeze – Light, variable direction Sailing Speed: 1/3 speed Sea State: Ripples, no waves Navigation/Visibility: Good unless fog. Crew may need to row or wait.
Wind Roll (2d6): 4 Wind Force & Direction: Gentle Breeze – Light steady wind (e.g. NE) Sailing Speed: 1/2 speed Sea State: Low waves, minor whitecaps Navigation/Visibility: Ideal fishing weather, ship stable, easy navigation.
Wind Roll (2d6): 5 Wind Force & Direction: Moderate Breeze – 10–15 mph Sailing Speed: 2/3 speed Sea State: 3 ft waves, regular whitecaps Navigation/Visibility: Normal. Slight roll, no penalties.
Wind Roll (2d6): 6–8 Wind Force & Direction: Fresh Breeze – 15–20 mph Sailing Speed: Normal (as per ship stats) Sea State: 3–6 ft waves, numerous whitecaps Navigation/Visibility: Good visibility. Ship heels slightly. Crew morale high.
Wind Roll (2d6): 9 Wind Force & Direction: Strong Breeze – 20–25 mph Sailing Speed: +1/3 speed (~133%) Sea State: 6–9 ft swells Navigation/Visibility: Horizon sometimes obscured by spray. -1 to precision tasks on deck.
Wind Roll (2d6): 10 Wind Force & Direction: High Wind – 25–30+ mph Sailing Speed: +1/2 speed (~150%) Sea State: 8–12 ft cresting waves. Deck may be awash Navigation/Visibility: Horizon obscured intermittently. Dex checks to move on deck safely.
Wind Roll (2d6): 11 Wind Force & Direction: Near Gale – 30–40 mph Sailing Speed: 200% if running with wind (reefed sails recommended) Sea State: 15+ ft waves, heavy pitching Navigation/Visibility: Poor. Spray and noise hinder communication. Hourly seaworthiness checks.
Wind Roll (2d6): 12 Wind Force & Direction: Gale/Storm – 40–80+ mph Sailing Speed: Wild. Most ships run with bare poles Sea State: 20–30+ ft waves. Rogue waves possible Navigation/Visibility: Near-zero visibility. Navigation lost. Crew at risk of injury or being swept overboard. Capsize and shipwreck possible near coastlines.
(Source: Synthesized from Poor Wizard’s Almanac sailing recommendations and OSE/Basic D&D rules for wind. The above speeds assume following winds; tacking into a gale is effectively impossible.)
Notes on Sailing: These mechanics assume a seaworthy vessel (a well-built caravel, longship, etc.). If the party is on a small boat or makeshift raft, reduce tolerances: even a “High Wind” (10 on the scale) could capsize a rowboat or canoe. In such cases, adjust difficulty: e.g. in high wind, a rowboat must reach shelter or risk capsizing (maybe a 2-in-6 chance each hour). An “Unseaworthy” vessel caught in a gale has an 80% chance to founder (sink) as per OSE.
Movement and Navigation: Under sail, movement is also affected by currents. OSE notes for river travel that currents can add or subtract 1d6+6 miles per day – at sea, currents are slower but vast. For simplicity, assume a steady current might add ~5-10 miles/day if going with it, or slow similarly against it. The prevailing current in Sea of Dread generally flows westward and then south (like an analogue of equatorial current), so voyages eastward may be slower. The DM can inform players that “The voyage back will likely take 2-3 days longer if the winds don’t shift.”
When it comes to getting lost at sea: if the party lacks a compass (the Known World does have compass technology in some cultures) or a skilled navigator, the risk is high. By OSE, with a navigator the chance to get lost is 2-in-6 in open sea, without one it’s basically certain if out of sight of land. The DM might allow Navigation proficiency to reroll or reduce that. If lost, you as DM secretly drift them off course by a few degrees each day of missed navigation. They might realize they’re lost only when expected land doesn’t appear on schedule. Stars can help at night if visible, but heavy clouds or storms make that moot. Encourage PCs to invest in charts and navigation tools if they plan extended voyaging.
Special Sea Hazards:
Storm Damage: After a gale or storm, evaluate the ship’s condition. Perhaps the vessel has taken on water (reduced speed until repaired at port – e.g. sails torn, so -1/3 speed, or hull sprung a leak requiring pumping). In game terms, you could say: “Your ship survived the storm, but the foremast is cracked – you’ll sail at -2 knots until it’s repaired at a dock.” This makes the players consider putting in for repairs or risk another storm with a weakened ship.
Fog: A calm morning fog bank can be an encounter itself. In dense fog, two ships might blunder into each other with little warning. Use the visibility note: only ~40 yards sight. In such conditions, sailors often drop to minimal sails and sound bells or horns. For PCs, fog might mean a risk of hitting reefs or an excuse for a ghost ship to appear out of nowhere. Navigationally, fog might cause a lost check if it lasts long.
Sargasso Sea: Module X6 Quagmire! famously involves a swampy area and possibly a “Sargasso” (floating seaweed mass). If relevant, you can include regions of thick seaweed that slow a ship (perhaps half speed) and foul rudders. Clearing a ship from a sargasso might take hours of labor with poles and blades. And who knows what lurks beneath (maybe some undead from sunken ships or a carnivorous plant monster).
St Elmo’s Fire & Omens: At the DM’s discretion, strange weather phenomena like St. Elmo’s Fire (glowing discharge on masts during electrical storms) can occur. Sailors see it as an omen from Protius or other Immortals. It’s harmless but eerie – could freak out passengers. Another phenomena: Water spouts (tornado over water) during thunderstorms. They move erratically and can smash a ship if hit. Treat a waterspout like a temporary whirlwhind: if it “attacks” a ship, require a save for the ship or take heavy damage (maybe equivalent to a siege engine hit). Encourage players to avoid or outmaneuver such things.
Using these mechanics, DMs can run the sea voyages in X1 and X6 with appropriate challenge. In Isle of Dread (X1), for instance, the journey to the isle might involve a period of doldrums (testing players’ patience and resource planning), then a sudden squall or monster attack. In X6 (Quagmire), the journey through the Great Waste’s coastal waters might have freak storms as the module’s plot suggests the climate is worsening. Always tie weather to plot or at least to mood: a dark omen can be conveyed by an unnatural storm, whereas a clear day with a following wind might signal hope and progress. And if players plan to navigate from one known port to another, weather can be a major factor in how long it takes and what they encounter. For realistic variability, you could pre-roll a week of wind: e.g. sequence of winds (Fresh, Fresh, Strong, Gentle, Gale, etc.) and play that out. But be ready to adjust if the story calls for it (perhaps delaying a storm until a dramatic moment).
Inland & Highland Regions (B2, CM1 – Temperate Inland and Norwold)
Travel in inland regions of the Known World will expose the party to a variety of temperate-zone weather patterns. Modules like B2 Keep on the Borderlands (set in a rugged border region, often assumed to be in the hills/forests of Karameikos or Darokin) and CM1 Test of the Warlords (set in far-northern Norwold, a subarctic realm) showcase two ends of the spectrum. We provide a general temperate climate summary (suitable for lowland inland areas of Karameikos, Darokin, Thyatis, Glantri, etc.) and note modifications for highland or subarctic areas (like Northern Reaches, Glantri’s alpine regions, and Norwold).
Temperate Inland Climate (Karameikos/Darokin/Thyatis heartlands): The heart of the Known World roughly corresponds to latitudes 30°–45° North, giving it a climate not unlike Mediterranean to continental Europe. According to Gazetteer climate descriptions: south of the Cruth Mountains (Karameikos, Thyatis coastal plains) the climate is moist and temperate with mild winters, Darokin and southern Glantri are warm and sunny, akin to southern France, and lands further north/east (Ethengar, Northern Reaches) get progressively colder or more overcaststockingthedungeon.blogspot.com. Here’s a seasonal breakdown for a typical inland area like Karameikos’s interior or Darokin’s plains:
Winter: Winters are cool to cold but not brutal in Karameikos lowlands. Daytime highs might be ~40–50 °F (5–10 °C) in deep winter, nights around 25–35 °F (-4–2 °C). Snowfall is light and infrequent in the low elevations – perhaps a couple of brief snowfalls in Kaldmont or Vatermont that melt within days. In Darokin (slightly further north and inland), winters are a bit colder – regular frosts and occasional lasting snow, especially in northern Darokin or higher elevations. Glantri (high valley) and Wendar see significant snow all winter. Rain is the main precipitation in southern areas: expect cold rain or sleet. Travel Impact: In Karameikos/Darokin lowlands, roads remain passable most of winter, though mud is a constant problem after rains. Rivers may ice at the edges but rarely freeze solid except in the far north or high altitude. Short winter days mean travelers have less daylight (as noted, ~10 hours at midwinter). Behavior: Trade slows but does not fully stop – caravans still move, though fewer. Villages focus on indoor work. Monsters: Many humanoid raiders retreat to winter lairs, especially in harsher climes; however, hungry wolves or owlbears might wander closer to settlements in search of food. Undead activity (being less tied to seasons) can actually become a primary winter threat in some areas – a graveyard that a vampire avoids in summer due to human activity might be a perfect haunt in the long winter nights. Mechanics: OSE’s movement rules note that heavy snow can drastically slow overland movement (possibly half or quarter speed if on foot). In these temperate regions, heavy snow is limited to a few days a year (if at all in Karameikos). The DM can handwave that travel takes an extra day during a snowstorm. More often, cold rain is the annoyance – it can cause exposure if characters don’t have warm/waterproof clothing. Consider having unprotected characters make a Con save or lose 1 hp/hour in near-freezing rain (cumulative hypothermia effect) until they dry off and warm up. One notable Mystaran winter event: Kaldmont 28 (year’s end) in later years is the Day of Dread (no magic) – in AC 1000 it’s not applicable, but individual DMs might still incorporate a “midwinter magic flux” for flavor. Also, Blizzards could occur in unusual cold snaps: e.g. AC 1006 in PWA had strange weather due to Immortal events. A freak blizzard in Karameikos could trap PCs; use sparingly as an extreme event (perhaps tied to a plot, like an artifact causing unseasonable cold).
Spring: Spring is a time of unpredictable weather. Early spring (Thaumont) can still feel like late winter – chilly rains, occasional frost in morning. By Flaurmont and Yarthmont (mid-late spring), days warm significantly (60s–70s °F / 15–25 °C highs) but nights remain cool. Rainfall is frequent: spring is the wettest season in much of the Known World, with frequent showers and some longer rainstorms as weather fronts move through. Thunderstorms are possible especially in late spring when air masses clash (warm afternoons followed by cold fronts). Travel Impact: After the thaw, mud is at its worst. Dirt roads become quagmires. Travel times can double on muddy roads or trails – wagons risk getting stuck. The OSE rules don’t explicitly require that level of detail, but as DM you can narratively slow the pace (“Your carriage gets bogged; you spend an extra half-day extricating it”). River levels rise with spring runoff, making ferry crossings riskier but also allowing boat travel earlier. In flood-prone areas like the Streel River in Darokin, there could be flooding of lowlands in spring. Behavior: Caravans resume in force by late spring. Farmers are in the field sowing crops whenever the ground is dry enough. Festivals: Spring equinox (Thaumont 1) is celebrated as planting festivals in agrarian communities – often a day of rest and ritual, meaning travelers might find villages less active (everyone at the shrine praying for good crops) or conversely enjoying a spring fair. Monsters: Hibernating creatures wake up hungry. This is the season for increased monster encounters – a bear (or owlbear) emerging skinny and irritable, giant insects hatching when the first warm days hit (giant wasp sightings start in Yarthmont, for example). Humanoid raiders often conduct spring raids to steal livestock or grain since their winter stores are low. Mechanics: If using random encounter checks, one might increase frequency slightly in spring to reflect this uptick in activity (or simply emphasize in descriptions how desperate some creatures are – maybe an encounter that would normally avoid the party now attacks recklessly out of hunger). Weather-wise, getting caught in rain is the big hazard. Visibility can be reduced in heavy rain (–2 penalty on ranged attacks, for example, and Perception checks to spot distant things). Travel can be miserable – consider morale: characters without decent gear might have lower morale or require a Wisdom save to avoid feeling depressed or irritable after days of rain (role-play opportunity). On the other hand, spring brings renewal – healing herbs sprout, animals breed (maybe the party encounters territorial beasts protecting their young). DMs might allow foraging for spring greens or mention that hunting is easier (more game out and about). Overall, spring is a mix: lots of life, but lots of rain.
Summer: Summers in the temperate inland regions are generally warm to hot, with periodic storms. By early summer (Klarmont), days reach mid-80s °F (around 30 °C) commonly, with some days creeping into the 90s in lowland areas. Humidity can be moderate (Karameikos has forests and marshes that add moisture). Thunderstorms are a hallmark of summer afternoons, especially after hot, humid mornings. PWA notes frequent afternoon thundershowers in these climes – for example, in Karameikos region, expect a pattern of a few clear hot days, then a day with a storm or heavy shower to break the heat, then repeat. There is no monsoon per se (unlike in the Sind desert or Savage Coast), but late summer (Fyrmont) often has the most violent storms and even the risk of tornadoes in flatlands. Travel Impact: Generally, summer is the easiest time to travel. Roads are dry and firm (except briefly right after storms). Rivers are lower by late summer (easier ford in some cases, though harder for boat travel in shallow sections). The long daylight (15+ hours by midsummer at 45°N) means parties can cover more ground if they want. However, heat can be an issue especially wearing heavy armor under the sun. In Karameikos’s mild Mediterranean climate, heat is less deadly than in a desert, but still – a warrior in full plate marching at noon might need a Constitution check on a 95°F day. DMs can enforce rest breaks (OSE expects 1 turn rest per 5 turns travel, so perhaps narrate that as taking shade in midday). Encounters and Behavior: People travel early and late to avoid midday heat, similar to desert-lite behavior, but not as extreme. Trade is in full swing – roads are busiest, inns crowded. Bandits often choose summer to launch ambushes (dry ground for quick getaways, and plenty of travelers to pick from). Monsters: Many monsters have their mating season in summer. You might encounter more aggressive animals or monsters protecting territory. Water sources begin to dry in late summer, forcing creatures to compete at remaining ponds (could drive an owlbear into an area it normally wouldn’t go, etc.). In forested areas, summer thunderstorms sometimes cause wildfires (via lightning strikes) – an adventuring party could literally find themselves fleeing a forest fire after a storm, adding an environmental peril. Also, insect swarms (normal or monster insects) peak in summer – e.g. a plague of locusts might strip farms (thereby causing local famine, unrest… a plot hook), or monster insects like giant dragonflies might be more numerous near swamps. Mechanics: The main weather mechanics to consider in summer are exhaustion from heat and storm effects. For heat: if PCs are doing strenuous activity in >90°F (32°C) in armor, consider a Constitution save each hour or level of exhaustion (disadvantage on ability checks, etc.) or simply enforce the OSE rest rule strictly. Provide narrative cues: “The sun is beating down, your chainmail is searing to touch, sweat pours – you may want to take a breather or remove some layers.” For storms: apply penalties during heavy downpour or lightning. In open terrain, if there’s thunder and lightning, characters in metal armor or holding metal weapons could (very rarely) be struck – maybe have them roll a save vs Breath if they happen to be the tallest thing in a flat area at the wrong time (lightning strike for 6d6 damage?). Generally, just use common sense: players often ask, “Can we travel during the storm or should we shelter?” – it’s usually wise to shelter for the hour or two of a severe thunderstorm (especially to avoid soaked gear or frightened horses). Flash floods can occur if they are in narrow valleys or canyons during sudden storms (something to watch in say the Borderlands canyon country). Summertime is also when miasmas or disease can spread (spoiled food in heat, mosquito-borne illnesses). If using disease mechanics, summer could increase chances for things like swamp fever or heatstroke. But these are optional gritty details.
Autumn: Autumn (Ambyrmont, Sviftmont, Eirmont) in temperate regions is harvest time and generally pleasant, though progressively cooling and wetter again toward the end. Early autumn (September-like, Ambyrmont) still has many warm days, but nights start to get crisp. Mid-fall (Sviftmont) brings beautiful foliage in deciduous forests, and more frequent rain systems as the first cool air masses from the north clash with lingering warmth. By late fall (Eirmont), frosts become common at night and the first snow flurries might appear in northern areas or highlands. Travel Impact: Early autumn is excellent for travel – dry roads (until late fall rains), moderate temperatures (no more brutal heat). Many caravans make a last push before winter to move goods. By mid-autumn, days shorten (down to ~12 hours by late fall), so travel gets naturally limited by daylight unless the party travels by night (which is longer now, but colder and riskier). Mud can return in late fall as frequent rains soak the ground that had been dry. If Eirmont (November) brings heavy rain, some dirt roads become muddy like spring. In cold regions, late fall rains might freeze overnight, causing icy patches on roads in the morning. Behavior: Harvest season means many villagers and even some monsters are focused on gathering food. You might find less banditry in early fall because bandits are busy secretly harvesting their hidden plots or raiding farm stores after harvest. However, once harvest is in and communities have full granaries (late fall), raids can spike – goblinoids and brigands love to steal a portion of that bounty before winter. That’s why many borderland keeps (like in B2) are on guard during late fall. Monsters: Animals grow more active and aggressive in fall in preparation for winter. You might see territorial clashes (stags locking horns – or monster equivalents). Some monsters like werewolves are often associated with autumn (harvest moons, etc.) – this is flavor, but perhaps their curses act up or more were-beasts are created during long autumn nights. In Ethengar and the steppes, Steppe fires can break out in early autumn when grass is dry before the rains come – a threat similar to a wildfire scenario. As leaves fall, visibility in forests improves – easier to spot things at distance compared to dense summer foliage (so ambushes might be noticed slightly earlier). Mechanics: If using encounter distance rules, perhaps increase by a bit in sparse autumn woods. Another mechanic: wind in late autumn storms can be quite strong (seasonal gales). A big November storm might down trees or make missile fire -2 to hit due to gusts if outdoors. Cold rain in late fall should encourage PCs to start unpacking warmer clothing or risk the cold exposure issues as in winter. One interesting phenomenon: fog is common in autumn, especially near bodies of water (warm days + cool nights = morning fog). This can set a scene – e.g. the Keep on the Borderlands might be shrouded in mist one morning, with goblin war drums echoing faintly… atmospheric and affects visibility until sun burns it off.
Northern Highlands and Norwold (CM1 Test of the Warlords): When the party ventures to more extreme climates (e.g. Norwold, which is around 60°N and includes subarctic conditions, or high-altitude areas like Glantri’s mountains, Rockhome, the Khurish Massif, etc.), adjust the above temperate expectations:
General: At 60°N (Norwold’s southern coast) the climate is roughly like Earth’s southern Alaska or Scandinavia. Winters are long and harsh, summers short and mild. Snow cover is common half the year or more. The PWA climate table for 60°N (Farend) shows winter daylight as only ~6.5 hours and summer daylight as 18+ hours – a dramatic swing. Northern regions also suffer “white nights” (very short darkness) in high summer and very short days in midwinter. This affects how you might schedule encounters (lots of nocturnal threats have limited hunting time in summer, but endless night in winter).
Winter (Far North): Expect heavy snow from mid-fall through spring. In Norwold, snow begins in early Kaldmont (if not late Ambyrmont) and accumulates through the winter. Snowpack several feet deep is normal in forests and plains, drifts can be much higher. Lakes and rivers freeze completely (thick enough to support sleds or even horse-drawn sleighs by deep winter). Temperatures routinely drop below 0°F (-18°C) in cold snaps, and highs might stay below freezing for weeks. Blizzards are a major hazard – winds and snow that can completely disorient travelers. In “hex-crawl” terms, movement in Norwold in winter without skis or snowshoes might be at 1/4 normal or worse. OSE doesn’t list snowshoes but logically a party can mitigate deep snow penalty by using them (perhaps up to 1/2 normal). Avalanches: In mountain areas, heavy snow plus a sudden thaw or loud noise can trigger avalanches (saving throw vs Death or take lots of damage if caught). Arctic monsters become more prevalent – white dragons, frost giants, winter wolves roam widely in winter months (sometimes even coming further south than normal). For example, a pass that’s safe in summer might have a frost giant hunting party in winter because they migrated down from higher peaks.
Summer (Far North): Summers are brief and cool. Norwold might see highs of 65°F (18°C) in the warmest month, occasionally a warm spell into 75°F (24°C) but nights remain chilly. Snow and ice melt leading to mud season in late spring/early summer. In marshy areas, summer brings out swarms of insects (the far north is notorious for mosquitoes/gnats in summer). That can be an environmental challenge (maybe impose minor distraction penalties or constitution checks to avoid getting “bugged” unless they have netting or repellent herbs). Crops that local settlers plant have to mature quickly – harvest likely in late summer as frosts can come even early fall. So the economic schedule is compressed. The sun barely sets at the height of summer – which means potentially no true night for a stretch. Undead or nocturnal monsters might be forced to lay low for weeks. This could advantage players (they can travel 18 hours a day with only minor fatigue if they wish), but it can also mess with sleep cycles (no dark – if no good window covers, maybe a penalty to rest?). Magical darkness or just sleeping masks solve that though.
Shoulder seasons: Spring and fall are almost skipped – winter dominates. E.g. Norwold’s spring might literally be two weeks of rapid thaw and mud in Thaumont, then it’s basically “light winter” until summer. Autumn might hit in late Ambyrmont – by early Sviftmont first snowfalls, etc. So planning expeditions is critical: an adventuring season might only be 4-5 months long before weather imprisons everyone.
Highlands (Mountains): Altitude mimics latitude. Glantri’s peaks or Rockhome’s high valleys have colder conditions than lowlands same latitude. A rule of thumb: +1000 feet elevation might equate to roughly 3°F (1.5°C) cooler temperature. So a pass at 6000 ft could be ~18°F cooler on average than sea level – turning a 40°F rain into a 22°F snow, for instance. Mountains also get heavier precipitation on windward sides. So a party crossing a mountain range even in summer could face pockets of perpetual snow/ice. The Canolbarth forest (Alfheim) in contrast has a magical climate moderation, always rather mild, but that’s an exception due to magic.
Mechanics for Cold: For extreme cold (subzero or intense windchill), similar to heat, require saves or damage. A simple system: if below freezing and improperly dressed, Save vs Poison each day (or each watch in truly frigid -20°F conditions) or take 1d6 damage and suffer exhaustion. Magical cold attacks (like white dragon breath) aside, just existing in -40 blizzard could be lethal without magic or shelter (could treat each hour exposure as a save or take 1d6 damage, cumulative). Provide ways to mitigate: cold weather clothing might give advantage or a bonus on those saves. Icing: equipment may freeze – e.g. rope becomes stiff, locks freeze (need heating or alcohol to open). A winter journey might require a good description of how PCs prepare (did they bring snowshoes, sleds, etc.?).
Conclusion: The Known World’s inland weather is diverse, but largely analogous to European temperate patterns, just remember Mystara’s year is slightly shorter so seasons might align a bit differently date-wise, and Immortal meddling or magical phenomena can always spice things up. Poor Wizard’s Almanac climate charts confirm these general behaviors (e.g. Rockhome in winter is extremely cold, Northern Reaches similar, Ethengar gets deep snow in winter and dusty winds in summer). The DM can always refer to Almanac region forecasts for flavor (like “blizzard likely in mountains” in Kaldmont or “dust storms likely in desert” in Yarthmont as cues for those times of year).
To ensure OSE consistency: Characters in temperate climates rarely face mechanical weather penalties beyond what’s logically described (rain making things wet, snow slowing movement). OSE doesn’t have a complex weather system in core, so use common sense: travel/day as per rules (24 miles in clear, 12 in forest, etc. for a 120’ movement human) can be adjusted situationally: halve it if mud or snow drastically impede, quarter if truly extreme. Foraging is generally good in temperate summers (plenty of game and edible plants), slim in winter (maybe automatic failure unless near evergreen forest with game). OSE encounter check frequency might be modified by weather: e.g. during a torrential downpour, maybe skip one check because even monsters hunker down. Or inversely, after a storm, maybe an extra check because predators resume hunting eagerly.
By incorporating these seasonal patterns, the DM can create a living world where players plan around weather. For example, before heading into the mountains in winter, perhaps NPCs warn them: “No one goes there until spring – the passes are closed.” If they go anyway, weather can become as big a foe as any dragon. Meanwhile, clear sunny days can be described to contrast earlier hardships (“After 3 days of slogging through rain, the sun finally breaks through. It’s a welcome sight – you dry your cloaks and enjoy the warmth, though mosquitos begin to hum around the puddles.”). Such details lend authenticity and encourage players to consider environment in their strategy (maybe they’ll say: “Let’s wait out the storm in the abandoned barn” or “We travel at first light to maximize daylight”).
This modular system – calendars, daily weather tables, seasonal summaries, and mechanical guidelines – is designed to support both DM logistical prep (so you can plan and adjust encounters based on weather or time of year) and player-facing immersion (through handouts like weather forecasts, notable celestial events, etc.). You can present the players with a “3-day weather forecast” table when they set off on a journey (based on the tables or your rolls), which might influence their choices (e.g. “We push hard today while it’s clear, because tomorrow’s forecast is stormy, we’ll rest then”). Include fun icons/symbols on such handouts: a sun for clear, a cloud for cloudy, raindrops, a lightning bolt, snowflake, etc., to make it easy to scan. Players appreciate knowing things like sunrise/sunset times if they plan stealth or travel – e.g. inform them “Sunset is around 6:30 PM now in autumn.” This lets them schedule watches or decide when to make camp in-game.
Finally, don’t forget solstices and strange weather patterns for mood: Use optional tables or prompts to introduce omens. For example, near every winter solstice, there might be a “Long Night” encounter table with eerie events: roll d6 – (1) an unnatural aurora lights the sky in green flames (no mechanical effect, just unsettling); (2) villagers report that all their winter store milk soured overnight (a bad omen for the year’s end); (3) on the coldest night, wolves howl a haunting chorus that seems almost speech – maybe an Immortal is sending a sign; (4) a fell fog rolls in that night, any caught outside must save vs Spells or be affected by a fear spell as dread fills their hearts; (5) the stars align in an unusual pattern (perhaps the Eye of Arik constellation glows red – foreshadowing an evil awakening); (6) a meteor shower streaks across the solstice sky – regarded by scholars as portent of significant events (perhaps correlating with an upcoming plot event). These have minimal direct mechanical impact but greatly enhance the mood and give perceptive players foreshadowing clues.
Likewise for summer solstice or equinoxes: maybe fey activity spikes – on midsummer night, travelers might encounter whimsical will-o’-wisps that lead them to a fairy circle (could be dangerous or rewarding). Or at equinox, day and night monsters might cross paths or a gate between realms flutters open briefly. You could make a small “Solstice Mysteries” table to roll on, ensuring each year in the campaign such celestial events have a unique twist.
By weaving together calendar lore, weather mechanics, and seasonal storytelling, you’ll create a richly textured wilderness experience. The party will literally feel the passage of time – trudging through spring mud, baking under summer suns, harvesting in autumn’s golden afternoons, and shivering in winter’s dark – which elevates a long campaign’s narrative spine. All these tools help transform wilderness travel from a mere line on the map into an immersive journey on Mystara, with nature as much a character in the story as any NPC.