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A 2D6 Science Fiction Supplement
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 violent weather. Determine the degree of instability with a throw of 1D6
Weather and add the modifiers in the table below for the planet’s overall climate,
©2020 Michael Brown its current season, its approximate period of rotation, and the
approximate latitude of the PCs’ current location. All four mods are
I looked up in alarm as a particularly loud thunderclap went off overhead. cumulative:
It must’ve also taken Vajra’s attention off our mission; as I glanced at
her, I saw her mouthing a silent prayer as she eyed the boiling blackness Climate Season Rotation Latitude
overhead. Warm +1 Spring +1 12– hrs. +2 0º (Pole) –2
Tropical +1 Summer 0 24 hrs. 0 ±15º –1
“The gods are angry today,” she said, almost in awe.
Hot +2 Fall –1 36+ hrs. –2 ±30º –1
I had to agree; the sky was certainly angry, anyway. The black Very Hot +3 Winter –2 ±45º 0
rainclouds took on a greenish cast off to the west. The rain itself was Torrid +4 ±60º +1
coming down in sheets. The wind was gusting to worrisome levels. And ±75º +2
the lightning…I knew we couldn’t stay exposed like this. ±90º (Equator) +3
I wished we could’ve waited this storm out in the ATV, but we had
chased our target across the subsector and The Colonel wasn’t about If the modified instability number equals 0 or less, then the weather
to let him get away after coming so close. Not to mention the fifty remains calm for that day. However, if the number is positive, reference
thousand creds we’d get for catching him. the table below to see how much it has changed (indicating that a
weather system has moved into the area):
But that lightning. And the rain…
Conditions Duration
I forced myself to focus. The Colonel and Berlin had circled ahead to 0 No activity n/a
flush the guy in our direction; we had to be ready. 1 Overcast +1D3 x 100%
The rain suddenly stopped, as though Vajra’s gods had decided enough 2 Overcast1 +1D6 x 100%
was enough and flipped the “off” switch. It was then that we both heard 3 Minor Storm, Local +0%
a loud, rushing sound. A jet engine, or…? 4 Minor Storm, Regional +0%
I looked westward, toward the noise. A few kilometers away, a spinning, 5 Major Storm, Local –50%
grayish-white finger of cloud was reaching toward the ground below. 6 Violent Storm2, Local –75%
Rope-thin at first, it gained girth as it touched down and announced its 7 Major Storm, Regional Cyclonic +300%3
presence with a roar of wind and a veil of black dust. Local: an area of up to 25 km
Regional: an area of 26-250 km, including squall lines
Vajra spat a barbarian profanity upon seeing the tornado and looked 1
Chance of precipitation per day is the planet’s Hydrographic
around frantically for cover. I did the same, suddenly deciding the
score or less on 2D6
mission — and the money — wasn’t that important after all. 2
Usually tornadic
3
Duration is the time is takes for the system to pass through the
Modeling weather in a roleplaying game is often a hit-or-miss area.
proposition. There are random tables, published and online, that can
help, but the results can sometimes be unrealistic, even silly. Add to that The current conditions persist in the area for 6D6 x 10 minutes. Adjust
the fact that meteorological processes can be almost impossibly this time by the Duration modifier in the table above. After this time, the
complex, and it’s no wonder many Referees simply don’t bother weather moves one step up the table toward “No activity” once again,
introducing weather into their games, or if they do, they relegate it to the with a new duration determined each time. This simulates the movement
background of a given weather system through the PCs’ present location and the
planet’s natural meteorological tendency toward stability.
But the addition of inclement or violent weather can add more to the
adventure than mere background or window-dressing. Indeed, a sudden The modified instability score also indicates the weather’s effects on
rainstorm or the appearance of a tornado as in the vignette above can vision, combat, and movement. Half of the instability (round off) is
add tension and spice to the action, serve as an additional complication applied as a negative DM to these actions due to wind, precipitation, and
for the PCs, and add color to what is supposed to be an alien darkness, doubled for heroes in a flying vehicle or otherwise aloft.
environment.
The type of precipitation depends on the current season and the type
This supplement for Cepheus Engine (CE) and the Original Science of storm. For example, winter precipitation on a Cold world is usually
Fiction Roleplaying Game (OSFRPG) gives the Referee the tools to snow, while precipitation during a violent storm might be hail.
emulate weather across an entire world – any world. While purely
realistic results are impossible due to the complexity of real-life weather Weather Creation Checklist
systems — for instance, the effect of such atmospheric mechanics as
Hadley cells aren’t covered here — this gross oversimplification of the 1) Determine the world’s Weather score (Wx)
process is sufficient for gaming purposes. Instead of meteorology, we’ll a. Wx = (Atmosphere x Hydrographics) ÷ Size
be using the concept of stability, which is, after all, a boiled-down 2) Once per local day, throw 2D6 for Wx or less
description of weather: a natural process of atmospheric instability a. If the throw is less than or equal to Wx, there is an
correction. See below for details. atmospheric instability that will try to correct itself.
i. Determine the degree of instability with a
Creating Weather throw of 1D6.
ii. Apply modifiers
To begin the process of creating a world’s weather, the Referee needs 1. Climate modifiers
three pieces of information: the world’s Universal Planetary Profile Size 2. Seasonal modifiers
(SIZ), Atmosphere (ATM), and Hydrographics (HYD) codes. Using the 3. Latitudinal modifiers
formula (ATM x HYD) ÷ SIZ, the Referee determines a basic Weather 3) Reference final result on Weather Conditions table.
Score (Wx). If Wx ends up less than 2, or ATM is zero, then the world a. Note Duration adjustments.
has no significant weather. However, in such cases, the Referee can
expand the definition of “weather” to include radiation/dust/solar storms, Other Applications
or meteor showers.
This ruleset need not be confined to meteorological effects. It can also model
The “default” weather condition is No activity (see table below.) Once such items as massive insect swarms (such as the local equivalent of
per local day, the Referee should throw Wx or less on 2D6 to determine locusts), motion of the aftereffects of a natural disaster (such as a volcanic
if there is an atmospheric instability resulting in inclement, sometimes ash cloud), or even planetary troop movements or animal migration.

Cepheus Engine and Samardan Press are the trademarks of Jason "Flynn" Kemp. The author is not affiliated with Jason "Flynn" Kemp or Samardan Press™.

Christopher Tulloch (Order #45738185)