Weather is important in role-playing games. This is especially true in wilderness and seafaring exploration adventures, where poor weather can affect navigation, travel speed, and visibility. Nearly all RPGs provide some way to randomly generate weather. One of the problems with random weather tables is that they tend to be “too random”. Rolling once a day on a random weather table can result in the weather jumping unrealistically between different types (Storm! Cold Weather! Hot Weather! Storm! etc). Real weather tends to vary over a few days, for example, mid-latitude weather tends to flip between regimes of unsettled stormy weather and regimes of settled weather (for example, heatwaves in summer or cold spells in winter associated with anticyclonic conditions).
“Less random” random weather using a simple Markov chain
A different way to create random weather and yet retain realistic variations is to expand on the idea of the weather flipping between “Settled” and “Unsettled” regimes using a method known as a Markov chain. The basic idea is that there is one roll per day to determine if the weather remains Settled or Unsettled, or if it flips to the other weather regime. There is then a second roll to determine the weather type. The second roll is done every day during an Unsettled weather regime to mimic the passage of storms and weather fronts. During a Settled regime, only one roll is made for the weather type, which then persists until the weather flips to the Unsettled regime again.
The tables below describe a method for generating realistic spring or fall (autumn) weather for a location similar to Southern England. Hopefully you’ll find this fairly simple to follow (or at least no more complicated than other RPG methods) – let me know in the comments.
Spring and Fall Weather Tables
- Roll 1d20 each day to determine if the weather remains Settled or Unsettled, or if it changes regime.
|Roll 1d20||Settled Weather Regime||Unsettled Weather Regime|
|1-14||Weather remains Settled||Weather remains Unsettled|
|15-20||Weather becomes Unsettled||Weather becomes Settled|
- Now determine the type of weather, which depends on regime:
For a Settled Weather Regime:
At the start of the regime, roll 1d20 to determine the type of Settled Weather. The type of Settled Weather persists until the weather becomes Unsettled.
|1-5||Cool & Foggy||No rain, morning fog then clear, calm, cool|
|6-10||Clear & Cool||No rain, clear, calm or light wind, cool|
|11-15||Clear & Warm||No rain, clear, calm or light wind, warm|
|16-20||Cloudy & Warm||No rain or light showers, cloudy, light wind, warm|
For an Unsettled Weather Regime:
Roll 1d20 each day to determine the type of Unsettled Weather.
|1-6||Clear & dry||No rain, clear, light wind, cool|
|7-11||Rain showers||Rain showers, cloudy, light wind, cool|
|12-17||Rain||Rain, cloudy, light to moderate winds, cool|
|18-20||Storm||Heavy rain, cloudy, moderate to strong winds, cool|
More details of the method can be found in the following blog post.
Some additional tables for summer and winter weather can be found here.
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More about Dungeons & Dragons OnlinePost: "Is random weather in role-playing games too random? Using simple Markov chains to make RPG weather more realistic" specifically for the game Dungeons & Dragons Online. Other useful information about this game:
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