Where would a campaign
world be
without weather? Whether you're creating
a campaign world or simply guiding a
party through a pregenerated dungeon or
wilderness adventure, the addition of
weather conditions that change day by
day and season by season adds realism
to
the game. After all, how realistic is
it to
allow player characters to wander
through a perpetually sunny and warm
world? There must be days when a heavy
rain soaks them to the skin, when the
sun
bakes down and causes painful sunburns,
when deep snowdrifts make movement
difficult, or when icy cold nights make
hypothermia a very real threat.
By including weather in a campaign,
characters are forced to think and prepare
ahead for jaunts through the wilderness
from one dungeon to another. In fact,
they
might even be forced into a dungeon or
two by the adverse weather conditions
they encounter along the way! Likewise,
a
party might be forced to "winter over"
in
some disreputable (and dangerous) little
h a m l e t .
The tables in this article can be used
either to add daily weather conditions
to
an individual game module, or to flesh
out
a campaign world by adding seasonal
weather patterns. The tables (and the
instructions for their use) present average
rainfalls and temperatures for 12 different
climatic zones based on those found on
Earth. By combining these tables with
those that deal with wind conditions,
realistic weather conditions for
any given
day or time of year at any point on an
Earthlike world can be determined.
A c a m p a i g n w e a t h e r s y s t e m
If you want a logical campaign world,
you want one in which terrains blend
gradually into one another and in which
weather patterns make sense. The first
step in designing any campaign world is
to
draw a map of the continent characters
will explore. But before you draw any
more than the outline of a continent,
determine where the lines of latitude
fall.
Latitude determines where your extreme
terrain and climatic zones (the deserts,
jungles, and icebound polar regions) lie.
Let's assume that you have a world
about the same size as the Earth. Using
this scale, there are 720 miles for every
1 0oof latitude. This gives a total of
6,480
miles between the equator (0° latitude)
and either pole (90° latitude).
If you want a continent that includes
everything from torrid jungles to glacierlocked
tundra, your map must include at
least 50° of latitude, or about 3,600
miles.
For the purposes of this weathergeneration
system, jungles can only lie
within about 20° of the equator, and
icebound regions are only found above 60°
latitude (with the rare exception of an
extremely high mountain range covered
with glaciers). Deserts
are found only
within 30° of the equator.
This means that if you use the common
game mapping scale of 24 miles to the
hex,
there will be 30 hexes between each 10°
of latitude, or three hexes per degree
of
latitude. To draw a continent that spans
15° latitude to 65° latitude,
you will need
150 hexes, top to bottom.
If this scale produces a map that is physically
too large to handle (it will be about
four graph pages wide), try a scale of
144
miles to the hex. Using this scale, there
are
only five hexes between each 10oof latitude
(enabling an entire continent to fit on
one sheet of graph paper).
The next step is to fill in the terrain
of
each hex (e.g., jungle, hills, broken
land,
etc.). Note the previously mentioned rules
for where jungles, deserts and polar
regions must be located.
Now you can start working out where
each of the 12 major types of climate
falls.
It is easy to spot where some go; for
example, a desert climate will be located over
desert terrain (and possibly a few surrounding
hexes of broken land). But locating other climatic zones takes more
thought.
After you've drawn a subsidiary map of
where the 12 climatic zones fall, it will
be
easy to work out exactly what type of
weather is occurring at any spot on the
map. Each climatic zone has a different
percentage chance for rainfall in any
given
month, and each has a different average
temperature for each month. Details on
each of the 12 climatic zones and where
they can be located follow.
Table 1
Month of Year
| 1d12 | Month |
| 1 | January |
| 2 | February |
| 3 | March |
| 4 | April |
| 5 | May |
| 6 | June |
| 7 | July |
| 8 | August |
| 9 | September |
| 10 | October |
| 11 | November |
| 12 | December |
Table 2
Weather Determination
| Terrain type | Where located | Latitude range | Climate category |
| Broken land | Inland | 0 - 2 0 ° | Desert |
| - | Inland | 21-40° | Warm with dry winter |
| - | Inland | 41-70° | Cool & rainy |
| - | Inland | 71-90° | Polar |
| - | Coastal | 0-20° | Desert |
| - | Coastal | 21-50° | Warm & rainy, or warm with dry summer |
| - | Coastal | 51-70° | Cool with dry winter |
| - | Coastal | 71-90° | Tundra |
| Desert | All | 0-30° | Desert |
| - | All | 31-90° | - |
| Forest | All | 0-20° | Tropical savvana |
| - | Inland | 21-50° | Warm with dry winter |
| - | Inland | 51-70° | Cool & rainy |
| - | Coastal | 21-50° | Warm & rainy, or warm with dry summer |
| - | Coastal | 51-70° | Cool with dry winter |
| - | All | 71-90° | - |
| Grassland (also Clear) | All | 0-20° | Tropical savanna |
| - | Inland | 21-50° | Steppe |
| - | Inland | 51-70° | Cool & rainy |
| - | Coastal | 21-50° | Warm & rainy, or warm with dry summer |
| - | Coastal | 51-70° | Cool with dry winter |
| - | All | 71-90° | Tundra, or polar |
| Hills | Inland | 0-20° | Tropical savanna |
| - | Inland | 21-40° | Warm with dry winter |
| - | Inland | 41-70° | Cool & rainy |
| - | Inland | 71-90° | Polar |
| - | Coastal | 0-20° | Tropical savanna |
| - | Coastal | 21-50° | Warm & rainy, or warm with dry summer |
| - | Coastal | 51-70° | Cool with dry winter |
| - | Coastal | 71-90° | Tundra |
| Jungle | Inland | 0-20° | Equatorial |
| - | Coastal | 0-20° | Monsoon |
| - | Coastal | 21-90° | (treat as forest) |
| Mountains | All | 0-20° | Warm with dry summer, or warm & rainy |
| - | Inland | 21-40° | Warm with dry winter |
| - | Inland | 41-70° | Cool & rainy |
| - | Inland | 71-90° | Polar |
| - | Coastal | 21-40° | Warm & rainy, or warm with dry summer |
| - | Coastal | 41-70° | Cool with dry winter |
| - | Coastal | 71-90° | Tundra |
| Swamp | Inland | 0-20° | Equatorial |
| - | Inland | 21-40° | Warm with dry summer |
| - | Coastal | 0-20° | Monsoon |
| - | Coastal | 21-40° | Warm & rainy |
| - | All | 41-90° | (as per surrounding terrain) |
Tables 3-14: Average Temperature by Climate
| General notes on Tables 3-14 |
| N: Northern hemisphere |
| S: Southern hemisphere |
| Temperatures drop at night by 5-30 F (5d6). A strong wind lowers temperatures in cold regions by 2-40 (2d20). |
| Temperature descriptions are relative to that climatic zone only. Thus, "cold" in a polar region does not describe the same temperature as does "cold" in a steppe region. |
Desert
Found primarily at the centers of continents
in low latitudes (0-30° latitude), this
arid climatic zone is dry and very hot.
At
night, deserts grow very cold, with temperatures
dropping by as much as 60°
(roll 6d10) overnight. This climatic zone
includes broken land and desert terrain.
Examples of Earth's deserts include northern
Mexico, north-central Africa, central
Australia, and all of Arabia.
Vegetation in these hot regions includes
drought-resistant plants with long, shallow
roots to absorb moisture from a large
area. Vegetation also tends to have thick
stems that store water and waxy plant
surfaces. Vegetation usually flourishes
only after the infrequent rainstorms,
when the desert "blooms." Plants lie dormant
between storms.
Table 3
Temperature: Desert
| 1d100 | Winter
(Dec-Jan, N) (May-Jun, S) |
Fall/spring/summer
(Feb-Nov, N) (Jul-Apr, S) |
| 01-05 | 55° F (cold) | 65° F (cool) |
| 06-95 | 65° F (cool) | 70-90° F (hot) |
| 96-00 | 70° F (warm) | 110° F (very hot) |
Tropical
savanna
Found inland of the monsoon climatic
zone in areas near the equator (0-20°
latitude), this climatic zone features
a
summer rainy season and a winter
drought. Such regions have hot grasslands
broken by scattered trees or patches of
forest.
Forests of thorny plants or patches
of scrub are also common. This climatic
zone includes forest, grassland, and hilly
terrain. Examples of tropical savannas
include central Africa and central India.
Table 4
Temperature: Tropical Savanna
| 1d100 | Year round |
| 01-05 | 75° F (warm) |
| 06-95 | 90-105° F (hot) |
| 96-00 | 115° F (very hot) |
Steppe
Found in the interiors of continents at
middle latitudes (20-50° latitude),
this dry
climatic zone combines low rainfall with
hot summer and cold
winter temperatures.
Due to the arid conditions, trees are
rare. Vegetation in these semidesert
regions includes grassland broken by
scrub. This climatic zone includes grass-.
land terrain only. Examples of steppes
include northern Africa, Argentina, and
central China.
Table 5
Temperature: Steppes
| 1d100 | Summer
(Jun-Aug, N) (Dec-Feb, S) |
Fall/spring
(Sep-Nov/Mar-May, N) (Mar-May/Sep-Nov, S) |
Winter
(Dec-Feb, N) (Jun-Aug, S) |
| 01-05 | 70° F (warm) | 50° F (cool) | 35° F (cold) |
| 06-95 | 85-95° F (hot) | 60-70° F (warm) | 40-45° F (chilly) |
| 96-00 | 110° F (very hot) | 80° F (hot) | 50° F (cool) |
E q u a
t o r i a l
Found in both coastal regions and the
interiors of continents, but always near
the equator (0-20° latitude), this
hot and
humid climatic zone features heavy rainfall
and high temperatures throughout the
year. There is, however, no distinctive
rainy season. This climatic zone includes
jungle and swampy terrain. Examples
include the upper Amazon basin, ?darkest?
Africa, and Indonesia.
In tropical rain
forests, vegetation is lush
and includes hundreds of species of
plants. Trees grow to a height of 130?,
and
the thick canopy of leaves formed blocks
the sunlight, making the forest floor
dark.
Vines and creeping plants make up the
bulk of the other forest plants.
Table 6
Temperature: Equator
| 1d100 | Year round |
| 01-05 | 60° F (unusually cool) |
| 06-95 | 70-85° F (hot) |
| 96-00 | 100° F (very hot) |
M o n s o o
n
Found in coastal areas near the equator
(0-20o latitude) that have strong, prevailing
winds from offshore, this climatic zone
is
characterized by hot weather and a distinctive
rainy season marked by heavy
tropical storms. Here again, the tropical
rain
forest predominates. This climatic
zone includes jungle and swampy terrain.
Examples include the coastal Amazon,
coastal India, and southeastern Asia.
Table 7
Temperature: Monsoon
| 1d100 | Year round |
| 01-05 | 70° F (warm) |
| 06-50 | 85-100° F (hot) |
| 51-95 | 100-110° F (very hot) |
| 96-00 | 120° F (extremely hot) |
W a r
m a n d r a i n y
Found at the edges of continents in
middle latitudes (20-50° latitude),
this
temperate climatic zone features steady,
moderate rainfall throughout the year.
Depending upon the latitude, the forests
found in this region can range from broadleaf
(at lower latitudes) to coniferous (at
higher latitudes); these two types of
forest
often shade into one another. This type
of
climatic zone includes broken land, forest,
grassland, hilly, and mountainous terrain.
Examples of warm and rainy climatic
zones include west coastal Canada, southeastern
United States, Europe, Japan,
southeastern China, New Zealand, eastern
Australia, and southeastern Brazil.
Table 8
Temperature: Warm and Rainy
| 1d100 | Summer
(Jun-Sep, N) (Dec-Mar, S) |
Fall/spring
(Oct/Mar-May, N) (Apr/Sep-Nov, S) |
Winter
(Nov-Feb, N) (May-Aug, S) |
| 01-05 | 60° F (cool) | 40° F (cold) | 10° F (very cold) |
| 06-50 | 65-70° F (warm) | 50° F (chilly) | 25-32° F (freezing) |
| 51-95 | 70-75° F (hot) | 60° F (cool) | 33-45° F (cold) |
| 96-00 | 85° F (very hot) | 65° F (very warm) | 50° F (cool) |
W
a r m with dry summer
Found in coastal areas in middle latitudes
(20-50° latitude), this temperate
climatic zone features a dry summer season.
Vegetation varies from scrub (at lower
latitudes) to thick coniferous forest
(at
higher latitudes). This climatic zone
includes broken land, forest,
grassland,
hilly, and swampy terrain. Examples of
warm with dry summer climatic zones
include Spain, the Mediterranean, and
Iran.
Table 9
Temperature: Warm With Dry Summer
| 1d100 | Summer
(May-Sep, N) (Nov-Mar, S) |
Fall/spring
(Oct-Nov/Mar-Apr, N) (Apr-May/Sep-Oct, S) |
Winter
(Dec-Feb, N) (Jun-Aug, S) |
| 01-05 | 60° F (cool) | 50° F (chilly) | 10° F (very cold) |
| 06-50 | 65-70° F (warm) | 60° F (cool) | 20-32° F (freezing) |
| 51-95 | 70-85° F (hot) | 65° F (warm) | 35-50° F (cold) |
| 96-00 | 95° F (very hot) | 70° F (very warm) | 60° F (warm) |
W
a r m w i t h d r y w i n t e r
Found inland in middle latitudes (20-40°
latitude), this temperate climatic zone
features dry winters. These regions tend
to have forests,
usually coniferous. This
climatic zone includes forest, hilly,
and
mountainous terrain. Examples of warm
with dry winter climatic zones include
the
southern interior of China, Bolivia, and
south-central Africa.
Table 10
Temperature: Warm With Dry Winter
| 1d100 | Summer
(Jun-Jul, N) (Dec-Jan, S) |
Fall/spring
(Aug-Oct/Mar-May, N) (Feb-Apr/Sep-Nov, S) |
Winter
(Nov-Feb, N) (May-Aug, S) |
| 01-05 | 70° F (warm) | 50° F (cool) | 32° F (frosty) |
| 06-95 | 85-90° F (hot) | 60-65° F (warm) | 35-45° F (chilly) |
| 96-00 | 110° F (very hot) | 70° F (hot) | 50° F (cool) |
C o o l
a n d r a i n y
Found in the central and eastern portions
of continents in high middle latitudes
(40-70° latitude), this temperate
climatic
zone features cooler temperatures and
consistent rainfall or snowfall. There
is no
variation in precipitation from one season
to another. Generally, this region is
covered with coniferous forests having evergreen trees well adapted to
colder
temperatures and snowfall. This zone
includes broken land, forest,
grassland,
hilly, and mountainous terrain. Examples
of cool and rainy climatic zones include
most of Canada, most of the U.S.S.R.,
and
Scandinavia.
Table 11
Temperature: Cool and Rainy
| 1d100 | Summer
(Jul-Sep, N) (Jan-Mar, S) |
Fall/spring
(Oct/Mar-Jun, N) (Apr/Sep-Dec, S) |
Winter
(Nov-Feb, N) (May-Aug, S) |
| 01-05 | 60° F (cool) | 35° F (cold) | 5° F (very cold) |
| 06-50 | 65-70° F (warm) | 40-50° F (chilly) | 15-25° F (cold) |
| 51-95 | 70-75° F (hot) | 50-60° F (cool) | 25-32° F (freezing) |
| 96-00 | 85° F (very hot) | 65° F (warm) | 40° F (chilly) |
C
o o l w i t h d r y w i n t e r
Found at the edges
of major continents
at high middle latitudes
(50-70° latitude),
become marshy and
fill with mosses,
lichens, and small
flowering plants. The
permafrost prevents
the growth of anything larger than dwarf shrubs.
At higher latitudes
(above 70° latitude),
the summer season
corresponds with an
extremely long day,
while the winter season corresponds with months of virtual
darkness. During
the summer, the sun is
overhead for about
23 hours per day.
During the winter,
the sun rises above the
southern horizon
for only about one hour
per day. The change
from one extreme to
another is gradual.
This climatic zone
includes clear,
hilly,
and mountainous
terrain. Examples
of tundra climatic zones
include northern
Canada, Alaska, northern U.S.S.R., and Tibet.
Table 12
Temperature: Cool With Dry Winter
| 1d100 | Summer
(Jul-Sep, N) (Jan-Mar, S) |
Fall/spring
(Oct/Mar-Jun, N) (Apr/Sep-Dec, S) |
Winter
(Nov-Feb, N) (May-Aug, S) |
| 01-05 | 60° F (cool) | 35° F (cold) | 5° F (very cold) |
| 06-50 | 65-70° F (warm) | 40-50° F (chilly) | 15-25° F (very cold) |
| 51-95 | 70-75° F (hot) | 50-60° F (cool) | 25-32° F (freezing) |
| 96-00 | 85° F (very hot) | 65° F (warm) | 40° F (chilly) |
T u n d r a
Found at high latitudes (above 70°
latitude) or in very high mountains
above 50°
latitude at the center of a continent,
this
cold climatic zone features low rainfall
(or
snowfall) and a short, warm summer,
when the top few inches of permafrost
(permanently frozen soil) thaw and vegetation
flourishes briefly. Flat areas then
become marshy and fill with mosses,
lichens, and small flowering plants. The
permafrost prevents the growth of anything
larger than dwarf shrubs.
At higher latitudes (above 70° latitude),
the summer season corresponds with an
extremely long day, while the winter season
corresponds with months of virtual
darkness. During the summer, the sun is
overhead for about 23 hours per day.
During the winter, the sun rises above
the
southern horizon for only about one hour
per day. The change from one extreme to
another is gradual. This climatic zone
includes clear, hilly, and mountainous
terrain. Examples of tundra climatic zones
include northern Canada, Alaska, northern
U.S.S.R., and Tibet.
Table 13
Temperature: Tundra
| 1d100 | Summer
(Jun-Jul, N) (Dec-Jan, S) |
Fall/spring
(Aug-Nov, Feb-May, N) (Feb-May/Aug-Nov, S) |
Winter
(Dec-Jan, N) (Jun-Jul, S) |
| 01-05 | 32° F (cold) | 10° F (very cold) | -15° F (extremely cold) |
| 06-50 | 35-40° F (chilly) | 15-20° F (cold) | -5-15° F (very cold) |
| 51-95 | 40-50° F (cool) | 25-32° F (freezing) | 15-32° F (freezing) |
| 96-00 | 65° F (warm) | 35° F (chilly) | 35° F (cold) |
P o l a r
Found at the center of large land masses
at high latitudes (above 70° latitude),
this
climatic zone features cold
average temperatures. This region is permanently
covered with snow and is almost completely
devoid of plant life, with only mosses and lichens on rocks that protrude
above the polar ice caps and glaciers.
This
climatic zone includes clear, hilly, and
mountainous terrain. Examples of polar
climatic zones include Greenland and
Antarctica.
Table 14
Temperature: Polar
| 1d100 | Summer
(Jun-Jul, N) (Dec-Jan, S) |
Fall/spring
(Aug-Nov/Feb-May, N) (Feb-May/Aug-Nov, S) |
Winter
(Dec-Jan, N) (Jun-Jul, S) |
| 01-05 | 32° F (cold) | 25° F (very cold) | -35° F (extremely cold) |
| 06-50 | 35-40° F (chilly) | 30° F (cold) | -25 to 0° F (very cold) |
| 51-95 | 40-50° F (cool) | 32° F (frosty) | 0 to 30° F (cold) |
| 96-00 | 65° F (warm) | 40° F (cool) | 32° F (frosty) |
P r e v a i
l i n g w i n d s
The direction of
the prevailing winds in
any area also helps
determine both the
type of climatic
zone and the general
weather conditions
found there. The
direction of the
prevailing wind determines whether lots of warm, moist air
sweeps across the
ocean and drops rain on
the land, whether
cold air blows down
from the poles,
or whether hot air moves
up from the equator.
On Earth, winds tend
to follow general
patterns, depending
upon the latitude of
each region. At
the equator, where the
sun?s rays provide
the most heating, air is
forced upward. Trade
winds blow toward
the equator from
about l5° latitude. Within the belt at 30-60° latitude, the prevailing
winds blow toward an imaginary
middle line at about
45° latitude. This
pattern exists in
both hemispheres.
Because the Earth
rotates on its axis, the
prevailing winds
do not blow directly
north or south.
Generally, prevailing
winds blow to the
northwest or southeast
in the southern
hemisphere, and to the
northeast or southwest
in the northern
hemisphere. Winds
blowing from the
direction of the
equator warm a region,
while winds blowing
down from the poles
cool a region.
Of course, the winds
in any region do
not always blow
in these directions. Local
terrain, prevailing
ocean currents, and
local weather patterns
all change the
course of the wind
slightly.
Table 15
Day-by-Day Precipitation1
| Climatic zone | Time of year | Daily chance
of rain/snow |
| Desert | Year round | 5 |
| Tropical savanna | May-Sep (rainy season) | 85 |
| - | Apr, Oct | 35 |
| - | Nov-Mar (dry season) | 10 |
| Steppe | Jul-Sep (dry season, N); | <-> |
| - | Jan-Mar (dry season, S) | 5 |
| - | Rest of year | 20 |
| Equatorial | Mar-May | 50 |
| - | Jun-Dec | 40 |
| - | Jan-Feb | 30 |
| Monsoon | Jun-Oct (rainy season) | 90 |
| - | Nov-May (dry season) | 15 |
| Warm and rainy | Year round | 40 |
| Warm with dry summer | Jun-Aug (N); Dec-Feb (S) | 10 |
| - | Rest of year | 30 |
| Warm with dry summer | Jun-Aug (N); Dec-Feb (S) | 10 |
| - | Rest of year | 30 |
| Warm with dry winter | Jul-Aug (N); Jan-Feb (S) | 45 |
| - | Rest of year | 15 |
| Cool and rainy | Year round | 35 |
| Cool with dry winter | Jul-Sep (N); Jan-Mar (S) | 35 |
| - | Nov-Apr (N); May-Oct (S) | 10 |
| - | Rest of year | 20 |
| Tundra/polar | Year round | 10 |
N: Northern hemisphere
S: Southern hemisphere
1 30 percentile dice rolls
(1d100) per month.
Table 16
Precipitation and Wind Type
| 1d6 | Rain/snow | Cloud type | Wind type1 |
| 1 | Light mist2/few flakes | A few clouds | A |
| 2 | Drizzle2/dusting | Mostly cloudy | B |
| 3 | Steady rainfall/flurries | Gray, slightly overcast | C |
| 4 | Strong rainfall/moderate snowfall | Gray, highly overcast | D |
| 5 | Pounding rain/heavy snowfall | Dark storm clouds3 | E |
| 6 | Downpour/blizzard4 | Dark storm clouds4 | F |
1 Reference these letters on
Table 17.
2 10% chance of fog if temperature
is above 32° F.
3 15% chance of electric storm.
4 20% chance of hail mixed
with snow.
Weather is made up of
four variables:
temperature, cloud cover, precipitation,
and wind.
Using the charts and tables
provided in this article, you can construct
a weather pattern for your own campaign
world. In doing so, here are a few general
guidelines to consider (remember, there
are exceptions.
1. Regions near the
equator experience
warmer temperatures and lack distinct
seasons. The further north or south an
area lies, the more distinct its seasonal
variations. Extreme examples would be
the icebound polar regions, the "lands
of
the midnight sun," which experience drastic
differences in the amount of sunlight
they receive from winter to summer.
2. Rainfall is heaviest
in terrains near the
equator and lightest at the poles.
3. Terrain that lies
inland, especially at
the center of a large land mass or continent,
experiences hte most dramatic
changes in temperature from one season
to the next. Large masses of high-pressure
air (associated with clear, dry weather
and
extreme heat or cold, depending upon the
season) build up at the centers of continents
where coastal winds cannot reach in
to push them aside.
Coastal terrains, however,
are more
temperate with fewer temperature
Table 17
Wind Type
| Letter1 | Die rolled |
| A | 1d4 |
| B | 1d6 |
| C | 2d4 |
| D | 2d6 |
| E | 2d8 |
| F | 2d10 |
1 Result taken from Table 16
extremes, due in part to the cooling (or
warming) effect provided by the large
mass of water nearby. In summer, the
ocean heats up at a slower rate than does
the land, and cool sea breezes blow in.
In
winter, the ocean stores warmth, and
warm sea breezes temper the winter. As
a
general rule, oceans heat up more evenly
than do land masses, both because the
sun?s rays can penetrate water to a greater
depth and because ocean currents circulate
and distribute the heat from the sun.
Temperate climates are also found in terrain
near very large lakes over which
prevailing winds blow toward the land.
4. Coastal regions experience sea
breezes on summer afternoons, while the
breezes blow from land to sea at night.
5. The higher the land elevation, the
lower the average temperature.
6. Elevation also affects precipitation.
Generally, rainfall (or snowfall) is caused
when warm, moist air is cooled and reaches
its dew or saturation point. Extra moisture held by the air is then dropped
in the
form of rain, snow, hail, or freezing
rain.
Air masses experience cooling as they
are forced upward, as when they travel
over hilly or mountainous terrain. For
this
reason, mountainous or hilly coastal areas,
where warm air is forced upward and
cooled, experience more rainfall than
areas inland. This is especially true
in
winter months, when warmer, moist air
sweeps in from the ocean and over the
colder land.
7. Areas on the lee side of mountains
(the side that faces away from the coast)
tend to be much drier, as they lie in
what
has been termed the ?rain shadow.? Here,
air traveling back down the other side
of
the mountains warms up and increases its
ability to hold moisture, resulting in
very
little rainfall. In fact, rain-shadow
regions
are often almost desertlike. Sometimes,
however, winds blowing down over the lee
side of a mountain range warm up so
quickly that they are capable of melting
up
to 10? of snow in a few hours. These
warm, dry winds are known as ?chinooks?
or ?foehns.?
8. In wide-open, flat regions, rainfall
is
caused by convection (vertical air currents).
As moist, sun-heated air is forced
upward, dark thunderclouds form and
drop rain. Often, the clouds drop hail
instead because the convection currents
have suddenly forced the moisture up into
an area with temperatures so low that
freezing occurs. The hailstones themselves
can be as large as 3? across.
Alternately, these clouds might drop
freezing rain during colder months. This
supercooled rain is liquid as it falls,
but it
instantly freezes upon hitting the ground,
coating everything with a layer of ice.
Precipitation in these areas is more likely
in the summer months, and summer
storms are often accompanied by thunder
and either fork lightning, which is likely
to
cause grass fires, or sheet lightning.
9. Occasionally, spring and summer
storms may produce tornadoes. An
intense thunderstorm can create between
30 and 40 tornadoes over an area several
hundred miles wide. Tornadoes are funnels
of rapidly rotating wind that usually
occur late in the afternoon. The funnels
are darkened by both moisture and dust,
and reach from the storm clouds overhead
down to the ground. A tornado funnel can
be several hundred yards wide at its base.
When the base of a funnel touches the
ground, it does great damage with winds
up to several hundred miles per hour.
As
the funnel mouth engulfs a building, the
air pressure outside the building lowers
suddenly and dramatically. The building
explodes outward, its windows, doors,
walls, and roof being blown off. Tornadoes
are accompanied by a loud roaring sound.
A tornado can pick up heavy objects and
carry them for several miles.
10. In lower latitudes where the prevailing
winds are from offshore, storms can
sometimes turn into hurricanes. Tropical
coastal regions usually experience about
10 major tropical storms per year (with
wind speeds of 40-70 MPH ? ?extremely
high? winds on Table 18), of which about
six reach hurricane strength. Hurricane
season lasts from September through
November (March through May in the
southern hemisphere).
Generally speaking, a hurricane is
defined as any tropical storm with wind
speeds of more than 70 MPH. Peak winds
in the average hurricane reach gusts of
about 180 MPH. These winds can uproot
large trees and knock over buildings.
Hurricanes are dangerous to ships
because they can whip ocean waves up to
60? high. They can also wipe out coastal
areas with a 10?-high wall of water that
precedes them, smashing into and over
low coastal regions. Prior to this, coastal
dwellers will be warned of the oncoming
hurricane by ocean swells.
Hurricanes typically move at a rate of
about 300 miles per day. When they reach
land, they cause heavy rainfall that may
lead to flooding. Hurricanes usually dissipate
and weaken once they move over a
land mass.
A hurricane, also known as a cyclone or
typhoon, affects a region for about two
to
seven days. A tropical storm several hundred
miles in diameter, the hurricane has
a central vortex or ?eye? of up to 300
miles
in diameter, in which winds are light
and
the skies are clear.
Using the weather tables
Using the weather tables
If you are just setting up your campaign
world and wish to establish a climate
and
weather system for it using this article,
follow these steps:
1. Establish whether the campaign area
is in the northern or southern hemisphere
of the campaign world.
2. Establish what month it is by rolling
1d12 and referencing Table 1 (or by picking
the month yourself). DMs should be
prepared to alter the months given in
this
article if their campaign worlds have
more
or fewer months, months of uneven
length, or (of course) months with different
names. In most cases, merely adjusting
for proportionate length should solve
time
problems. Months are only used as handy
time units, and need not be based
upon
lunar cycles.
3. Establish the campaign area?s terrain:
broken land, desert, forest, grassland
(includes clear), hills, jungle, mountains,
or
swamp. If a party?s travels take them
through a number of different types of
terrain, weather may have to be worked
out on a day-by-day basis.
4. Establish whether the type of terrain
is inland or coastal. Here, coastal terrain
is
any terrain within 96 miles of ocean or
within 48 miles of very large lakes.
5. Establish the latitude of the terrain
(equator = 0° latitude; poles = 90°
latitude). There are about 720 miles between
each 10o of latitude for Earthlike worlds.
6. Consult Table 2 to find the climatic
type (listed as types A-L).
7. Consult the temperature tables (Tables
3-14) for average temperatures for that
month. Most temperatures fall within the
average range for the month; however,
there is a 5% chance that it will be unusually
warm, and a 5% chance that it will be
unusually cold that month. Also, make
sure to note the possible temperature
changes caused by nightfall, and by strong
winds in cold regions.
8. Consult the day-by-day precipitation
tables (Tables 15 and 16). Assuming that
Table 18
Wind Speed (Based on Beaufort Scale)
| Die result1 | Type | Speed (in MPH) | Description |
| 1 | Calm | Less than 1 | Smoke rises vertically |
| 2-3 | Light air | 1-3 | Wind direction shown by smoke but not wind vanes |
| 4-5 | Light breeze | 4-7 | Wind felt on face, leaves rustle, and ordinary vanes move |
| 6-7 | Gentle breeze | 8-12 | Leaves and small twigs sway and banners flap |
| 8-9 | Fresh breeze | 13-18 | Small branches move, and dust and small branches are raised |
| 10-11 | Strong breeze | 19-24 | Small trees sway and small waves form on inland waters |
| 12-13 | Moderate gale (or near gale) | 25-31 | Large branches move |
| 14-15 | Fresh gale (or gale) | 32-38 | Whole trees sway and walking against wind is an inconvenience |
| 16-17 | Strong gale | 39-46 | Twigs break off trees and general progress is impeded |
| 18 | Strong gale | 47-54 | Slight structural damage occurs |
| 19 | Whole gale (or storm) | 55-63 | Trees are uprooted and considerable structural damage occurs |
| 202 (1-8) | Storm (or violent storm) | 64-72 | Widespread damage occurs |
| 20 (9-10)2 | Hurricane | 73-136 | Widespread devastation occurs |
1 Die result taken from Table
17
2 Whenever a 20 is rolled,
roll 1d10 thereafter. If the result is 9-10, consider the result a hurricane
each month has 30 days, roll percentile
dice 30 times, noting how many rainy/
snowy days result. Rainy/snowy days may
be scattered throughout the month or may
be grouped together as a period of ?bad
weather.? If you wish to determine randomly
when rainy days come, roll 1d30 to
determine which days will have precipitation,
ignoring any results already rolled. If
almost every day of the month is rainy/
snowy, roll to see which days are dry.
If you choose to group the rainy/snowy
days together, roll 1d30 to see on which
day of the month the bad weather begins,
If this roll produces weather that doesn?t
?fit? within the month ? for example,
eight days of rain starting on the 30th
(or
within the time period during which characters
will be traveling through that terrain) ? roll again until the bad weather
fits within the month, or have the bad
weather end on the last day of the month
and extend backward from there.
Construct a logical weather pattern --
Table 19
Wind Direction
| 1d8 | Wind blows toward: |
| 1 | North |
| 2 | Northeast |
| 3 | East |
| 4 | Southeast |
| 5 | South |
| 6 | Southwest |
| 7 | West |
| 8 | Northwest |
for example, drizzle, broken clouds, and
light winds on the first day or two, building
to moderate rain and wind, then heavy
rain and wind, then back to drizzle again
(see the next paragraph). To help characters
predict the weather, throw in a few
cirrus (high wispy) clouds on the last
sunny day to foreshadow the rain to come.
Note that wind can occur without precipitation,
but clear, windy days usually precede bad weather. To determine the wind
strength on a random windy day, roll 1d8
and consult Table 18.
Before determining a weather pattern,
consult Table 16 to see how heavy this
precipitation gets (at its worst). Even
though the bad weather may span several
days, it may never be any more than a
light drizzle or dusting of snow.
Note that certain regions will experience
only one type of precipitation. In deserts
(and in the dry seasons for tropical savannas
and steppes), rainfall may be light or
heavy, but it will usually rain for no
more
than one day, and not for a two- or threeday
period. In equatorial or monsoon
regions, the rainy season tends to produce
rainfall almost every day, usually a downpour,
and usually at the same time each
day (late afternoon).
Now, write down the weather pattern
you have produced on a chart for that
particular month. Using this procedure,
DMs must roll up weather for a month at
a time. An even better idea, however,
is to
roll up weather for a year (or at least
a
season) at a time. This way, the weather
for each month can ?blend? into the next
month?s in a logical way.
If questions arise as to what direction
the wind is blowing, consult Tables 16-19.
Final note
The effects of magic, whether cast by
deities or by player characters, are not
addressed herein. You can assume that
local alterations of weather by PCs are
so
short-lived that no other consequences
occur, or you can logically plot out some
more serious effects if such magic is
used
too regularly. A city that possesses an
artifact (or a large group of spell-casters)
that ensures good weather
may find this
artificial control of nature has unpleasant
side effects outside the city?s limits.
Use
your imagination ? and enjoy the
weather.