Home >Gamemastering >Environment >

Weather


While many of the physical dangers a group faces in the wilds vary significantly based on the nature of the terrain they explore, the weather can pose an array of challenges within a single region. When the weather is calm or good, it can make even the most unpleasant of terrains less grueling, but when the weather turns bad, even gently rolling hills, idyllic woodlands, and pastoral plains can become death traps.

While you can simply decide what the weather’s up to at any point in your campaign—and indeed you should always feel free to have it start raining, thundering, or gusting with wind when the story is enhanced by dramatic shifts in the weather—you can also use the following system to generate weather for your game.

In keeping with the goal of providing a shared game experience first and foremost, this system for generating weather is narrative-based rather than a fully scientific simulation. While this system takes into account generalities such as climate, elevation, and season, its primary focus allows you to set the norms for weather in a particular area of your choice, using a number of broad categories based on general climate and favored terrain categories. You can then add weather details and events outside that norm, from mere hassles to catastrophes, either randomly generating those weather events or picking and choosing ones that support your campaign’s greater narrative. This makes it easier for PCs whose classes enhance their skills in certain terrain types to better thwart environmental dangers that are created or provoked by such terrains’ weather.

Weather Baseline

When determining weather for a region in your campaign, your first step is to establish the weather baseline for the region. The weather baseline is influenced by the region’s climate (this sets the baseline temperature), elevation (this provides the baseline precipitation intensity), and season (this affects the temperature and dictates the baseline precipitation frequency).

Climate

Your first step in determining a region’s baseline weather is to decide upon the region’s climate. Climate is split up into one of three categories: cold, temperate and tropical. These types correspond to the three climate categories used in monster entries (note that a fourth category, extraplanar, is not a factor in determining weather for Material Plane worlds).

The baseline temperature range for each climate category is given below, and is further refined in Temperature Variations and Precipitation. These baselines are also presented in Table 4–12.

Extreme Temperatures

Temperatures of 40° F and lower or 90° F or higher are hazardous, growing more dangerous the more extreme they become. Without the benefit of endure elements or some other form of protection, characters exposed to temperatures beyond these ranges run the risk of taking damage and suffering other effects.

Cold: A cold climate is found in the extreme northern or southern regions of the world at latitudes greater than 60 degrees (approximately 2,000 miles from a pole). In these polar regions, temperatures often remain below freezing throughout the majority of the year. The baseline temperature in this climate is cold, ranging from 20º F in the winter, to 30º F in the spring and fall months, and up to 40º F in the summer. For regions within 500 miles of the pole, the baseline temperature is 10º F colder than the seasonal average. For regions within 250 miles of the pole, the baseline temperature is 20º F colder than the seasonal average. Because cold air tends to be drier than warm air, reduce the frequency and intensity of precipitation by one step in cold climates.

Temperate: Temperate climates stretch between the polar regions and tropical regions of the world, generally at latitudes between 60 degrees and 30 degrees. The baseline temperature in this climate ranges from 30º F in winter, to 60º F in spring and fall, and all the way up to 80º F in summer. Precipitation frequency is not altered as a result of a temperate climate, but it can still be altered as a result of other factors such as the elevation or season (see below).

Tropical: The tropics exist to either side of the world’s equator, extending north and south for about 30 degrees of latitude in either direction. Tropical regions tend to be warm and humid, with a baseline temperature ranging from 50º F in winter, to 75º F in spring and fall, and up to 95º F in summer. Because warm, humid air produces a great deal of precipitation, increase the frequency and intensity of precipitation by one step in this climate.

Elevation

While the climate sets baselines for temperatures, elevation plays a key factor as well. Elevation can affect the baseline temperature, and it sets the baseline intensity of precipitation in the region, as explained below and displayed in Table 4–13: Elevation Baselines.

Sea Level: Temperatures in sea-level and coastal regions are 10º warmer. Sea-level regions also tend to have more precipitation than areas of higher elevation, so the baseline precipitation intensity in a sea-level region is heavy.

Lowland: Lowlands are areas of low elevation not near the coast, generally at an elevation of 1,000 to 5,000 feet. This elevation range does not alter baseline temperatures. The baseline precipitation intensity in lowlands is medium.

Highland: Highlands include regions with elevations above 5,000 feet. Decrease baseline temperatures in highlands by 10º (although in particularly arid and flat regions, you should instead increase the baseline temperature by 10º, while in particularly high-altitude regions such as significant mountain ranges, you should instead decrease the baseline temperature by 20º). The frequency of precipitation is decreased by one step, and baseline precipitation intensity is medium.

Season

A year has four seasons—spring, summer, fall, and winter—each of which lasts about 3 months. Season plays an important part in dictating a region’s baseline temperature (as noted in each climate and in Table 4–14). It also dictates the baseline precipitation frequency in a region before applying adjustments due to climate or elevation. In most regions with cold and temperate climates, precipitation frequency is intermittent during spring and fall, common during the summer, and rare during the winter. In most regions with tropical climates, precipitation frequency is common during spring and fall, intermittent during the summer, and rare during the winter.

On worlds with a tilt in their axis, the seasons are typically reversed between northern and southern hemispheres. While it is the height of summer in the north, the areas south of the equator are in the depths of winter.

Temperature Variations And Precipitation

Once you have established weather baselines for a region and adjust them to match the elevation and season, the next step is to breathe life into the weather by determining the temperature’s variation from the adjusted baseline and the daily precipitation. With this system, you can build out weather patterns and events as far as you want into the future. If the PCs will be in a region for some time, it’s a good idea to plan out the weather’s variations and events at least a week in advance so if a character tries to use Survival to predict the weather, you’ll have information to work with. On the other hand, if you know the PCs are going to be in a region for only a few days, planning our a full week of weather isn’t necessary. And of course, you can randomly generate weather on a day-by-day basis if you’re comfortable with the possibility of an unexpected turn complicating the game’s other events.

Temperature Variations

Weather is constantly changing, and a significant aspect of that change is the temperature. For the purposes of this system, it’s easiest to assume that the daily temperature remains relatively static during daylight hours and then drops by 2d6+3 degrees during the night.

When setting a day’s temperature in a terrain, you can roll on the temperature variations table appropriate to the climate; the result determines how you should alter the adjusted baseline temperature, and also suggests the duration of that change. You can also use the tables without rolling for a result, consulting them as a guide to help you make decisions about variations in temperature.

For terrain in a cold region, roll on Table 4–15: Cold Region Temperature Variations. Temperature variations in this climate trend colder and last for a long period of time.

Precipitation

The next step in setting the local weather is to determine whether precipitation occurs and the intensity of that precipitation, if any.

Precipitation Frequency: Precipitation frequency is organized into five levels: drought, rare, intermittent, common, and constant. A region’s baseline precipitation frequency is set by the season, but it can be modified by the climate and other factors (for example, see the Deserts sidebar). A precipitation frequency can’t be reduced lower than drought or increased higher than constant. Check each day to determine whether precipitation occurs for that day; the percentage chance of precipitation occurring is summarized on Table 4–18: Daily Precipitation Chances.

For terrain in a temperate region, roll on Table 4–16: Temperate Region Temperature Variations. Temperature variations in this climate are about as likely to swing warmer or colder, and such variations tend to last for shorter periods. If you need to establish a day’s temperature for terrain in a temperate region, you can roll on Table 4–17: Tropical Region Temperature Variations. Temperature variations for tropical climates trend warm but for even shorter periods.

Table 4–12: Climate Baselines
Climate Winter Temp. Spring Temp. Summer Temp. Fall Temp. Precipitation Adjustment
Cold 20º F 30º F 40º F 30º F Decrease frequency and intensity by one step
Temperate 30º F 60º F 80º F 60º F
Tropical 50º F 75º F 95º F 75º F Increase frequency and intensity by one step
Table 4–13: Elevation Baselines
Elevation Altitude Range Baseline Temp. Adjust. Baseline Precipitation Intensity
Sea level Below 1,000 ft. +10º F Heavy
Lowland 1,000 ft. to 5,000 ft. Medium
Highland Above 5,000 ft. –10º F Medium (decrease precipitation frequency by one step)
Table 4–14: Seasonal Baselines
Season Cold or Temperate Climate Precip. Frequency Tropical Climate Precip. Frequency
Spring Intermittent Common
Summer Common Intermittent
Fall Intermittent Common
Winter Rare Rare
Table 4–15: Cold Region Temperature Variations
d% Variation Duration
1–20 –3d10° F 1d4 days
21–40 –2d10° F 1d6+1 days
41–60 –1d10° F 1d6+2 days
61–80 No variation 1d6+2 days
81–95 +1d10° F 1d6+1 days
96–99 +2d10° F 1d4 days
100 +3d10° F 1d2 days
Table 4–16: Temperate Region Temperature Variations
d% Variation Duration
1–5 –3d10° F 1d2 days
6–15 –2d10° F 1d4 days
16–35 –1d10° F 1d4+1 days
36–65 No variation 1d6+1 days
66–85 +1d10° F 1d4+1 days
86–95 +2d10° F 1d4 days
96–100 +3d10° F 1d2 days
Table 4–17: Tropical Region Temperature Variations
d% Variation Duration
1–10 –2d10° F 1d2 days
11–25 –1d10° F 1d2 days
26–55 No variation 1d4 days
56–85 +1d10° F 1d4 days
86–100 +2d10° F 1d2 days
Table 4–18: Daily Precipitation Chances
Frequency Chance of Precipitation
Drought 5% (decrease precipitation intensity by two steps)
Rare 15%
Intermittent 30%
Common 60%
Constant 95%

Precipitation Intensity: The baseline precipitation intensity is dependent on the elevation and can be modified by the climate. Intensity has four categories. Light precipitation is the lowest level of intensity and generally consists of fog, a faint drizzle of rain or a few isolated flakes of snow. Medium precipitation represents a noticeable but not distracting fall of rain or snow. Heavy precipitation typically consists of a driving rainstorm or significant snowfall. Torrential precipitation is the highest level of intensity and consists of a deluge of rain or snow with conditions that can approach whiteout levels. Precipitation intensity can never be reduced below light or increased above torrential.

Once you establish the intensity and the temperature, you’ll determine how the precipitation manifests.

Precipitation Form: Precipitation can result in more than just rain. Depending upon the intensity and temperature, precipitation can range from a light fog or a faint drizzle of rain to a blizzard or thunderstorm. Once you know precipitation of a specific intensity is occurring, set the time of day the precipitation event occurs by rolling 1d12 to find the starting hour of the day and 1d6 to determine whether the hour is a.m. or p.m. (1–3 = a.m., 4–6 = p.m.).

Next, use the appropriate table below for the baseline precipitation intensity and whether the temperature is above or below freezing (32° F) to generate the specific type of precipitation and its duration. (Remember that the temperature is lower at night!) See the Cloud Cover section for the effects of precipitation on visibility for flying creatures.

Deserts

Deserts are found in places where the weather must pass over mountains, causing a rain shadow, and in very cold environments. The baseline precipitation frequency in a desert is usually drought, but can be rare for a few weeks per year.

Table 4–19: Light Unfrozen Precipitation
d% Precipitation Duration
1–20 Light fog 1d8 hours
21–40 Medium fog 1d6 hours
41–50 Drizzle 1d4 hours
51–75 Drizzle 2d12 hours
76–90 Light rain 1d4 hours
91–100 Light rain (sleet if below 40° F) 1 hour
Table 4–20: Light Frozen Precipitation
d% Precipitation Duration
1–20 Light fog 1d6 hours
21–40 Light fog 1d8 hours
41–50 Medium fog 1d4 hours
51–60 Light snow 1 hour
61–75 Light snow 1d4 hours
76–100 Light snow 2d12 hours
Table 4–21: Medium Unfrozen Precipitation
d% Precipitation Duration
01–10 Medium fog 1d8 hours
11–20 Medium fog 1d12 hours
21–30 Heavy fog 1d4 hours
31–35 Rain 1d4 hours
36–70 Rain 1d8 hours
71–90 Rain 2d12 hours
91–100 Rain (sleet if below 40° F) 1d4 hours
Table 4–22: Medium Frozen Precipitation
d% Precipitation Duration
1–10 Medium fog 1d6 hours
11–20 Medium fog 1d8 hours
21–30 Heavy fog 1d4 hours
31–50 Medium snow 1d4 hours
51–90 Medium snow 1d8 hours
91–100 Medium snow 2d12 hours
Table 4–23: Heavy Unfrozen Precipitation
d% Precipitation Duration
1–10 Heavy fog 1d8 hours
11–20 Heavy fog 2d6 hours
21–50 Heavy rain 1d12 hours
51–70 Heavy rain 2d12 hours
71–85 Heavy rain (sleet if below 40° F) 1d8 hours
86–90 Thunderstorm 1 hour
91–100 Thunderstorm 1d3 hours
Table 4–24: Heavy Frozen Precipitation
d% Precipitation Duration
1–10 Medium fog 1d8 hours
11–20 Heavy fog 2d6 hours
21–60 Light snow 2d12 hours
61–90 Medium snow 1d8 hours
91–100 Heavy snow 1d6 hours
Table 4–25: Torrential Unfrozen Precipitation
d% Precipitation Duration
1–5 Heavy fog 1d8 hours
6–10 Heavy fog 2d6 hours
11–30 Heavy rain 2d6 hours
31–60 Heavy rain 2d12 hours
61–80 Heavy rain (sleet if below 40° F) 2d6 hours
81–95 Thunderstorm 1d3 hours
96–100 Thunderstorm 1d6 hours
Table 4–26: Torrential Frozen Precipitation
d% Precipitation Duration
1–5 Heavy fog 1d8 hours
6–10 Heavy fog 2d6 hours
11–50 Heavy snow 1d4 hours
51–90 Heavy snow 1d8 hours
91–100 Heavy snow 2d12 hours

Drizzle: Drizzle reduces visibility to three-quarters of the normal range, imposing a –2 penalty on Perception checks. It automatically extinguishes tiny unprotected flames (candles and the like, but not torches).

Fog, Heavy: Heavy fog obscures all vision beyond 5 feet, including darkvision. Creatures 5 feet away have concealment. Heavy fog typically occurs early in the day, late in the day, or sometimes at night, but the heat of the midday usually burns it away. Heavy fog occurs only when there is no or light wind.

Fog, Light: Light fog reduces visibility to three-quarters of the normal ranges, resulting in a –2 penalty on Perception checks and a –2 penalty on ranged attacks. Light fog typically occurs early in the day, late in the day, or sometimes at night, but the heat of the midday usually burns it away. Light fog occurs only when there is no or light wind.

Fog, Medium: Medium fog reduces visibility ranges by half, resulting in a –4 penalty on Perception checks and a –4 penalty on ranged attacks. Medium fog typically occurs early in the day, late in the day, or sometimes at night, but the heat of the midday usually burns it away. Medium fog occurs only when there is no or light wind.

Rain: Rain reduces visibility ranges by half, resulting in a –4 penalty on Perception checks. Rain automatically extinguishes unprotected flames (candles, torches, and the like) and imposes a –4 penalty on ranged attacks.

Rain, Heavy: Heavy rain reduces visibility to one-quarter of the normal range, resulting in a –6 penalty on Perception checks. Heavy rain automatically extinguishes unprotected flames and imposes a –6 penalty on ranged attacks.

Sleet: Essentially frozen rain, sleet has the same effect as light snow, but any accumulation typically doesn’t last longer than 1–2 hours after the storm.

Snow, Heavy: Heavy snow reduces visibility ranges to one-quarter of the normal range, resulting in a –6 penalty on Perception checks. It extinguishes unprotected flames and imposes a –6 penalty on ranged attacks. Heavy snow impedes movement even before it begins to stick. Moving into a square during a heavy snowstorm requires 1 extra 5-foot square of movement (this stacks with difficult terrain). Every hour of heavy snow leaves 1d4 inches of snow on the ground. As long as at least 2 inches of snow remain on the ground, the requirement of an extra square of movement to enter a square of snow persists. If at least 1 foot of snow remains on the ground, 2 extra squares of movement are required to enter a snow-filled square instead. A heavy snowstorm has a 10% chance of generating thundersnow and has a 40% chance of becoming a blizzard if the wind speed is severe or stronger.

Snow, Light: Light snow reduces visibility to three-quarters of the normal range, resulting in a –2 penalty on Perception checks. Light snow has a 75% chance each hour of extinguishing unprotected flames and imposes a –2 penalty on ranged attacks. Light snow does not impede movement unless it continues for 2 or more hours, at which point moving into a square of such snow requires 1 extra 5-foot square of movement (this stacks with difficult terrain). Every 2 hours of light snow leaves 1 inch of snow on the ground. As long as at least 2 inches of snow remain on the ground, the requirement of an extra square of movement to enter a square of snow persists. If at least 1 foot of snow remains on the ground, entering a snow-filled square instead requires 2 extra squares of movement.

Snow, Medium: Medium snow reduces visibility ranges by half, resulting in a –4 penalty on Perception checks. Medium snow extinguishes unprotected flames and imposes a –4 penalty on ranged attacks. Medium snow does not impede movement unless it continues for 1 hour, at which point moving into a square of such snow requires 1 extra 5-foot square of movement (this stacks with difficult terrain). Every hour of medium snow leaves 1 inch of snow on the ground. As long as at least 2 inches of snow remain on the ground, the requirement of an extra square of movement to enter a square of snow persists. If at least 1 foot of snow remains on the ground, entering a snow-filled square instead requires 2 extra squares of movement.

Thunderstorm: Thunderstorms feature powerful winds and heavy rain (see above). To determine the type of wind associated with the thunderstorm, roll on Table 4–27: Thunderstorm Winds.

Table 4–27: Thunderstorm Winds
d% Thunderstorm Wind Strength
1–50 Strong winds
51–90 Severe winds
91–100 Windstorm

In addition, there is a 40% chance that a thunderstorm features hail either up to an hour before or during the storm. An even greater danger presented by a thunderstorm is the lightning that occurs during the storm. These electrical discharges, generated by the roiling clouds, can pose a hazard to creatures that do not have proper shelters, especially creatures clad in metal armor. Every 10 minutes during a thunderstorm, a bolt of lightning strikes an unsheltered creature at random (though this can strike wildlife as easily as PCs). A creature struck by this lightning must succeed a DC 18 Reflex saving throw or take 10d8 points of electricity damage (a successful saving throw halves the damage). Creatures in metal armor take a –4 penalty on the Reflex saving throw.

There is a 10% chance that a thunderstorm with winds of windstorm strength also generates a tornado, while thunderstorms with windstorm-strength winds in temperatures higher than 85° F also have a 20% chance of being a precursor to a hurricane. There is a 20% chance that a thunderstorm of any strength in the desert also generates a haboob.

Weather Details

While temperature and precipitation are important aspects of weather, other details can add further danger and drama. Powerful winds can complicate weather, cloud cover can obscure vision, and special, often destructive weather events can cause incredible mayhem and widespread devastation.

Weather Underground

In extensive underground regions, the absence of a day-night cycle results in much different weather patterns. In large part, you can assume that weather is a nonissue for adventures that take place in regions like these, but some supernaturally enhanced caverns might have magical effects that mimic surface conditions, while others might have their own strange weather such as constant clouds of glowing spores (treat as fog), a constantly leaking ceiling (treat as rain), and so on. It’s generally best to pick and choose weather effects in the Deeplands, since this affords you more control and helps to keep the Deeplands feeling strange and alien—it’s a realm where even the weather cannot be reliably predicted.

Wind

Once you’ve generated the day’s precipitation, you’ll need to establish the wind strength unless the precipitation indicates otherwise. For example, on foggy days, no significant wind occurs, while thunderstorms have their own rules for determining wind strength. To set the wind strength for the day, roll d% and consult the table above.

The following describes the categories listed in Table 4–28: Wind Strength.

Wind Strength: This is the category of the wind strength.

Wind Speed: This is the range of wind speeds that occur. Wind speed typically fluctuates between these values through the period of the day, and for moderate or higher wind strength, there are periods in the day when the wind speed dips below the listed range.

Ranged Weapon Penalty/Siege Weapon Penalty: These are the penalties that characters take when firing ranged weapons and siege weapons in wind of the listed strength. In windstorm-strength wind, normal ranged weapon attacks (either projectile or thrown) are impossible. This includes ranged attacks made via spells of the conjuration school, but it does not include evocation ranged attacks. Siege weapons include all weapons of that type and boulders thrown by giants and other creatures with the rock throwing special attack.

Check Size: Creatures of the listed size or smaller are unable to move forward against the force of the wind unless they succeed at a DC 10 Strength check (on the ground) or a DC 20 Fly check if airborne.

Blown Away Size: Creatures of the listed size on the ground are knocked prone, roll 1d4×10 feet, and take 2d6 points of nonlethal damage, unless they succeed on a DC 15 Strength check. Flying creatures of the listed size are blown back 2d6×10 feet and take 2d6 points of nonlethal damage due to battering and buffeting, unless they succeed at a DC 25 Fly check.

Skill Penalty: This is the penalty for skill checks that can be affected by the wind. These penalties always apply on Fly checks and sound-based Perception checks, but GMs may also wish to apply them on Acrobatics checks, Climb checks, and any other ability or skill checks that could be adversely affected by winds.

Table 4–28: Wind Strength
d% Wind Strength Wind Speed Ranged Weapon Penalty/Siege Weapon Penalty Check Size Blown Away Size Skill Penalty
1–50 Light 0–10 mph —/—
51–80 Moderate 11–20 mph —/—
81–90 Strong 21–30 mph –2/— Tiny –2
91–95 Severe 31–50 mph –4/— Small Tiny –4
96–100 Windstorm 51+ mph Impossible/–4 Medium Small –8

Cloud Cover

You can roll on Table 4–29: Cloud Cover to determine the cloud cover for the day. Light and medium cloud cover mainly serve as thematic elements. Overcast conditions grant concealment for creatures flying at high altitudes. Overcast conditions without precipitation increase the temperature in fall and winter by 10° F and decrease the temperature in spring and summer by the same amount. If precipitation occurs, the cloud cover functions as overcast.

Table 4–29: Cloud Cover
d% Cloud Cover
1–50 None
51–70 Light clouds
71–85 Medium clouds
86–100 Overcast

Severe Events

On rare occasions, weather can produce truly dramatic and dangerous events. The following severe effects are sometimes generated by extreme precipitation. For instance, thunderstorms can create or be a harbinger for haboobs, hail, tornados, wildfires, or even hurricanes. At other times, certain types of precipitation combined with higher wind strengths can generate these severe events.

Blizzard: A combination of severe or stronger winds with heavy snow can create blizzard conditions. Blizzards reduce range of vision to no more than 20 feet, and even then, creatures takes a –8 penalty on Perception checks within that range. In a blizzard, the snowfall increases to 4 inches of snow each hour, and travel in more than 3 feet of snow is usually impossible without snowshoes or an ability such as waterwalk. Furthermore, the high winds make it feel (and affect living creatures) as if the temperature were 20° F colder. There is a 20% chance that a blizzard lasts for 2d12 hours instead of the normal duration for heavy snow.

Haboob: A haboob is a sandstorm created by a thunderstorm. See Sandstorm below for its effects.

Hail: Hail typically occurs just before or during a thunderstorm. Hail does not reduce visibility, but the sound of falling hail imposes a –4 penalty on sound-based Perception checks. Rarely (5% chance), hail pellets can become large enough to deal 1d4 points of lethal damage per minute to creatures and objects out in the open.

Hurricane: Hurricanes are incredibly massive storms featuring heavy rain and a wind strength greater than that of the most powerful windstorm. With winds of 75–174 miles per hour, a hurricane renders ranged attacks impossible, and siege weapons take a –8 penalty on attack rolls. Large or smaller creatures must succeed at a DC 15 Strength check or they are unable to move forward against the strength of the wind. Medium or smaller creatures on the ground must succeed at a DC 15 Strength check or they are knocked prone and roll 1d6x10 feet, taking 1d6 points of nonlethal damage per 10 feet. Flying creatures must succeed at a DC 25 Fly check or they are blown back 2d8×10 feet and take 4d6 points of nonlethal damage due to battering and buffeting. Hurricanes also usually cause flooding. It’s nearly impossible to journey out into a hurricane unscathed.

Sandstorm: Sandstorms occur when severe or greater winds kick up sand and debris in a desert or similarly arid environment. Sandstorms reduce visibility to 1d10×10 feet, and those within them take a –6 penalty on Perception checks. Sandstorms deal 1d3 points of nonlethal damage per hour to creatures caught in the open.

Thundersnow: High winds in a snowstorm can create the rare phenomena known as thundersnow. Lighting strikes are less common in thundersnow, but just as deadly. Every hour during the storm, a bolt of lightning strikes an unsheltered creature at random (though this can strike wildlife as easily as PCs). A creature struck by this lightning must succeed a DC 18 Reflex saving throw or take 10d8 points of electricity damage (a successful saving throw halves the damage). Creatures in metal armor take a –4 penalty on the Reflex saving throw.

Tornado: With winds with speeds of 174–300 miles per hour, tornados are deadly terrors. The smallest tornados occupy a 20-foot-radius burst, with winds of windstorm strength swirling up to 100 feet beyond that burst. The largest tornados can be 100-foot-radius bursts, with a windstorm whose radius extends 500 feet beyond that burst. Ranged attacks, including normal, siege, and even those produced by evocation spells, are impossible in the core burst of a tornado. Huge or smaller creatures must succeed a DC 20 Strength check or be sucked up by the funnel of the tornado; this deals 8d8 points of bludgeoning, piercing, and slashing lethal damage to the creatures. This damage ignores all but DR/epic, DR/—, and hardness. Once it deals this damage, the tornado flings the creature it has sucked up 1d20×10 feet up and away from the tornado, dealing 1d6 points of falling damage per 10 feet that the creature is flung. Gargantuan and larger creatures take the 8d8 points of damage but are not moved by the tornado. A tornado moves at a speed of 40 feet, though the direction it moves is entirely unpredictable—you can determine the direction randomly each round. Tornados typically last for 3d6 minutes, but some can swirl for up to an hour. While most tornados are created by thunderstorms, some smaller tornados (typically with a 5- to 10-foot-burst radius, with no outer radius) can be created in areas of wildfire (firenados), snow (snownados), or sand (dust devils). They deal a similar amount of damage, but firenados deal fire damage, snownados deal cold damage, and dust devils deal bludgeoning damage only, and these types of tornados do not fling their targets.

Wildfire: While wildfires can be sparked a number of ways, for these rules, they are usually created by a lightning strike in a particularly dry area of forest or other vegetation. Use the rules for forest fires, but add a 10% chance of the fire producing 1d6 firenados (see Tornado above).

Special Weather Events

Extreme Weather by Raging Swan Press

Source Wilderness Dressing: Extreme Weather. © Raging Swan Press 2013; Author: Mike Welham.

Storms have many game effects that can contribute to make encounters and combats unique and exciting. See Running a Rain Storm, Running a Wind Storm, and Running a Snow Storm for some interesting options for storms in your campaign or adventure.

Running a Rain Storm

Rainstorms can slow or halt travel and turn trails and tracks into quagmires. Travelling in a rainstorm – while not necessarily dangerous – can be miserable.

Rainstorms have the following game effects:

  • Visibility: Visibility during normal rain is halved, resulting in a -4 penalty on Perception checks; rain also imposes a -2 penalty on ranged attacks, and it extinguishes unprotected flames.
  • Wind: During a rainstorm, the wind increases such that it reduces visibility by three-quarters, resulting in a -8 penalty on Perception checks; these storms also render ranged weapon attacks impossible (with the exception of siege weapons, which take a -4 penalty on attack rolls), automatically extinguish unprotected flames and have a 50% chance to extinguish protected flames (such as from lanterns).
  • Thunderstorms: Thunderstorms have the additional hazard of lightning, which strikes once per minute in a one-hour period at the storm’s centre (decrease this as the PCs move away from the centre); each bolt causes between 4d8 and 10d8 electricity damage.
  • Colder Climates: In colder conditions, hail sometimes accompanies or replaces rain in a storm, where it imposes an additional -4 penalty on sound-based Perception checks and creates difficult terrain where it falls; hail has a 5% chance to be large enough to deal 1 damage to unprotected creatures.
  • Possible Tornado: Each thunderstorm has a 10% chance of producing a tornado (extinguishes all flames, renders all ranged attacks impossible—including siege weapons, renders all sound-based Perception checks impossible and pulls creatures who fail a Fortitude save into the funnel—dealing 6d6 damage per round for 1d10 rounds before expelling the creature and dealing falling damage).
Running a Snow Storm

Snowstorms dump a lot of snow over an area in a short amount of time. This hinders travel, can lead to travellers getting lost and – in extreme cases – can kill those caught out in them.

Snowstorms have the following game effects:

  • Normal Snowfall: Normal snowfall has the same effects as rain (reduces visibility by half that results in a -4 penalty on Perception checks, -2 penalty on ranged attacks and extinguishes unprotected flames); a day’s worth of snowfall leaves 1d6 inches of snow on the ground, and this forces a cost of 2 squares of movement to enter a snow-covered square.
  • Heavy Snowfall: Heavy snowfall has the same effects as normal snowfall, but it also grants concealment (20% miss chance) to creatures 5 or more feet away; this snow leaves 1d4 feet of snow on the ground, which hinders movement such that it costs 4 squares of movement to enter a square covered with heavy snow.
  • Snowdrifts: Windy conditions during heavy snow result in snowdrifts 1d4 x 5 feet deep, usually around objects large enough to deflect the wind.
  • Heavy Snow: Heavy snow has a 10% chance to have a thunderstorm accompany it. As with thunderstorms that occur with rain, lightning strikes once per minute in a one-hour period at the storm’s centre (decrease this as the PCs move away from the centre); each bolt causes between 4d8 and 10d8 electricity damage. For snowstorms, lightning is less severe, so the damage tends toward the range’s lower end.
  • Blizzard: A blizzard is the most powerful snowstorm, combining high winds (severe or worse), heavy snow measuring 1d3 feet, and bitter cold (requiring a Fortitude save every 10 minutes [DC 15, +1 per previous check] to avoid taking 1d6 nonlethal damage).
  • Sleet: Sleet and frozen rain can occur during winter storms, and it has the same effect as rain (however, the chance to extinguish protected flames increases to 75%), and, once it has fallen, it imposes a cost of 2 squares when entering a square affected by the precipitation.
Running a Wind Storm

Powerful windstorms can damage or destroy property and make travel impossible.

Windstorms have the following game effects:

  • Gusts of Wind: Windstorms rarely occur with precipitation, but gusts of wind during thunderstorms can hit extremes approaching a windstorm’s power (or exceed them when a thunderstorm spawns a tornado).
  • Windstorms: Windstorm-force winds can bring down tree branches, and sometimes whole trees, automatically extinguish unprotected flames, have a 75% chance of extinguishes protected flames, render ranged weapon attacks impossible, impose a -4 penalty on attack rolls for siege weapons, inflict a -8 penalty on Perception checks that rely on sound, and impose a -8 penalty on Fly checks.
  • Flying Creatures: Medium or smaller creatures attempting to move against windstorm-force winds must make a DC 10 Strength check, or a DC 20 Fly check for airborne creatures; windstorm-magnitude winds knock Small or smaller creatures on the ground prone and push them 1d4 x 10 feet (dealing 1d4 points of nonlethal damage per 10 feet), unless they make a DC 15 Strength check; for airborne creatures of size Small or smaller, the wind blows them back 2d6 x 10 feet and deals 2d6 points of nonlethal damage (which a flying creature can avoid with a successful DC 25 Fly check).
  • Hurricanes: Hurricane force winds act like windstorm-force winds with the following exceptions: they impose a -8 penalty on siege weapon attacks, render Perception checks based on sound impossible, check Large or smaller creatures, blow away Medium or smaller creatures and impose a -12 penalty on Fly checks.
  • Tornadoes: Tornadoes impose even greater penalties: siege weapon attacks become impossible, and tornadoes check Huge or smaller creatures; instead of blowing away Large or smaller creatures, a tornado pulls them toward it 2d6 x 10 feet if a creature fails its Strength or Fly check, and a creature making contact with the funnel as a result gets picked up and whirled around within the funnel for 1d10 rounds (taking 6d6 per round), after which the tornado ejects the victim, possibly inflicting falling damage.
  • Dust Storms: Dust storms are related to windstorms, except they have severe rather than windstorm-magnitude winds; they smother unprotected flames, have a 50% chance of extinguishing protected flames and deposit 1d6 inches of sand.
  • Great Dust Storms: Greater dust storms are accompanied by windstorm-force winds, deal 1d3 nonlethal damage and pose a choking hazard (a PC with a scarf or other protection starts choking after a number of rounds equal to 10 + Constitution score) to those without shelter, and deposit 2d3-1 feet of sand.

Storms

The combined effects of precipitation (or dust) and wind that accompany all storms reduce visibility ranges by three-quarters, imposing a –8 penalty on Perception checks. Storms make ranged weapon attacks impossible, except for those using siege weapons, which have a –4 penalty on attack rolls. They automatically extinguish candles, torches, and similar unprotected flames. They cause protected flames, such as those of lanterns, to dance wildly and have a 50% chance to extinguish these lights. See Table: Wind Effects for possible consequences to creatures caught outside without shelter during such a storm. Storms are divided into the following three types.

Duststorm (CR 3): These desert storms differ from other storms in that they have no precipitation. Instead, a duststorm blows fine grains of sand that obscure vision, smother unprotected flames, and can even choke protected flames (50% chance). Most duststorms are accompanied by severe winds and leave behind a deposit of 1d6 inches of sand. There is a 10% chance for a greater duststorm to be accompanied by windstorm-magnitude winds (see Table: Wind Effects). These greater duststorms deal 1d3 points of nonlethal damage each round to anyone caught out in the open without shelter and also pose a choking hazard (see Drowning, except that a character with a scarf or similar protection across her mouth and nose does not begin to choke until after a number of rounds equal to 10 + her Constitution score). Greater duststorms leave 2d3–1 feet of fine sand in their wake.

Snowstorm: In addition to the wind and precipitation common to other storms, snowstorms leave 1d6 inches of snow on the ground afterward.

Thunderstorm: In addition to wind and precipitation (usually rain, but sometimes also hail), thunderstorms are accompanied by lightning that can pose a hazard to characters without proper shelter (especially those in metal armor). As a rule of thumb, assume one bolt per minute for a 1-hour period at the center of the storm. Each bolt causes between 4d8 and 10d8 points of electricity damage. One in 10 thunderstorms is accompanied by a tornado.

Powerful Storms

Very high winds and torrential precipitation reduce visibility to zero, making Perception checks and all ranged weapon attacks impossible. Unprotected flames are automatically extinguished, and protected flames have a 75% chance of being doused. Creatures caught in the area must make a Fortitude save or face the effects based on the size of the creature (see Table: Wind Effects). Powerful storms are divided into the following four types.

Windstorm: While accompanied by little or no precipitation, windstorms can cause considerable damage simply through the force of their winds.

Blizzard: The combination of high winds, heavy snow (typically 1d3 feet), and bitter cold make blizzards deadly for all who are unprepared for them.

Hurricane: In addition to very high winds and heavy rain, hurricanes are accompanied by floods. Most adventuring activity is impossible under such conditions.

Tornado: In addition to incredibly high winds, tornadoes can severely injure and kill those that get pulled into their funnels.

Special Weather

Black Blizzard

Source: Pathfinder #7

Emberstorms, known also as “black blizzards,” are powerful duststorms composed of ash and embers left behind by large brushfires. An emberstorm typically takes hours to pass. These violent duststorms typically occur during summer months, when wildfires are more common. Winter emberstorms are seen as particularly bad omens but those that occur during the summer have become little more than an accepted way of life. The natural lay of the land shapes and funnels the path of an emberstorm to a certain extent, and knowledgeable tribes seek out lowlying areas like these out of habit. The edge of the storm assaults those it envelopes with strong winds of 30 mph. Anyone within the storm’s edge suffers a –10 penalty on Perception checks as well as missile attacks beyond ten feet. In addition, targets in the storm’s outer rim benefit from concealment (a 20% miss chance).

The wind deeper in an emberstorm can reach windstorm levels, but is normally severe wind. The scouring ash and grit in the air in an emberstorm functions as a typical duststorm, save that they normally leave behind only 1d4–1 feet of dust and ash in their wake. Additionally, whenever a character takes nonlethal damage from an emberstorm, he also takes 1 point of fire damage from the hot ashes.