On the Generation of Weather

Lately I've been thinking a lot about the weather.

I read a thread recently posted by a fan of those niche story games claiming without example that because rules light games rely on rulings that everyone playing them must want to just play freeform games.

You see, the whole idea of player-facing rules light play is to:
            A) Allow the Dungeon Master to be an impartial adjudicator
            B) Allow players to engage in fiction based problem solving
            C) Lower the barrier of entry to play

In other words, the games are explicitly well designed to do exactly that.

Which, strangely enough, brings me to the weather.

The whole gestalt of this rulings based play is a dynamic organic campaign. These are often called sandbox campaigns, because you know, it's about playing. Rarely do you find one of these rules-light games running adventure paths where the characters just move onto the next scene. The players drive the campaign.

One of my fondest memories of gaming was a Tower of Silence that had at some point been converted into a watchtower and then abandoned. It was abandoned because at night, the bodies rose from the dead and haunted the tower.

One line of notes on a six-mile hex map.

The players left the city and headed west. The day started out sunny, then at night it began to storm badly (because of the random weather table). I didn't need a rule to determine what sleeping in the rain would do to the players and neither did they.

They, of course, took cover in the watchtower. MUCH TO THEIR SURPRISE it was not a calm night.

It was a good organic emergent moment. The best kind in role playing.

It's these small things, calendars and weather, that lead to this kind of emergent long-term play. And that's sort of the problem with it. The weather generator is random. Even one for seasons, roll on it daily and it begins to cause problems with suspension of disbelief. This is even more important for fantasy setting where weather can include spellstorms, fire tornados, and ice growths. If you're feeling bad you've never had a fire tornado storm, don't. There's always your next session.

It's the calendar and weather and structure of society that come into conflict. How to create a realistic weather table with as little bookkeeping as possible?

Well I'm glad you asked. If you're playing in the Forgotten Realms, your work is already done for you. They have this nice utility that lets you determine the weather on any day in any year any place in the Forgotten Realms. If you're not running that though, and I'm not, you'll need a weather table.

My requirements are that it has to organically simulate weather, require minimal bookkeeping and fit on one page in a 4"x6" notebook.

Today I'm going to be developing the weather table for The Frigid Realm of Exquisite Stasis named Etah-naris of Peitharchia, the Child Czar of Equilibrium. She is a devil lord in Perdition. This is fairly simple, because in Etah-naris, there are no seasons, only the eternal winter of Peitharchia. It means we don't have to worry about the Merwish calendar, the months, or seasons. We only have to worry about the weather.

Having lived in the frozen wasteland for half a decade, I know how the weather is in such a place. There are relatively long periods of similar weather, punctuated by blizzards and storms. Weather is so important to that living feeling to a campaign because areas are defined by their weather. It's always consistent in the same way, even if it's highly variable during certain seasons, it's consistently highly variable.

I'm going to point out one more thing before we begin. Don't let yourself turn this into a lot of work. You don't need weather tables for anything but the current season and the current area. It can be a substantial length of real world time before you have to make another.

This is my second draft of the table, the first one was smaller. I realized I wanted more possible consecutive repeating days. Making the table 18 entries instead of 12 and primarily using 1d6 increased my odds of similar weather over 3 days from 42% to ~60%. A table with 24 entries and primarily using a d8 would give similar weather ~70% of the time.

I generally determine weather a week (10 days) at a time, although you could simply track it day by day and make it part of your hexcrawl procedure simply by noting the die roll you need for the next day. You roll 1d4 to start and simply roll the dice next to the entry to determine the weather for the next day.

1.      Clear, Sunny 40º (1d4)
2.      Clear, Cool 30º (1d4)
3.      Clear, Windy 10º (1d6+3)
4.      Clear, Crisp 0º (1d6+4)
5.      Clear, Cold -10º (1d4+2)
6.      Cloud, Cold -20º (1d6+12)
7.      Bitter, Windy -20º (1d4)
8.      Bitter, Windy -40º (1d6+6)
9.      Freezing, Windy -20º (1d4+2)
10.  Freezing, Windy -40º (1d6+6)
11.  Freezing, Windy -60º (1d4+7)
12.  Cloudy, Freezing -40º (*)
13.  Light Snowfall 0º (1d4)
14.  Light Snowfall -20º (1d6+12)
15.  Light Snowfall -40º (1d6+12)
16.  Heavy Snowfall 0º (1d4)
17.  Heavy Snowfall -20º (1d6+12)
18.  Heavy Snowfall -40º (*)

The * indicates that the roll is a 1d8+12 roll, with natural results of 7 or 8 indicating a roll on the Storm Subtable

Storm Subtable
1)      Snowstorm: The snowstorm lasts 4d12 hours. During the storm visibility is limited to 10 feet. Outdoor travel distance is cut by 1/2 and unless a target 8 survival check is made, direction is random. After the storm there is fresh snow over the ground augmenting all tracking checks and causing all covered terrain to be considered difficult for the next 5 days.
2)      Blizzard: A blizzard lasts 1d4+2 days. Visibility is 0. Outdoor travel distance is reduced to 1/4 normal and is always in a random direction. After the storm there is fresh snow over the ground augmenting all tracking checks and causing all covered terrain to be considered difficult for the next 5 days.
3)      Hail/Sleet: A hailstorm lasts 2d12 hours. Each exploration turn a save must be made or characters take 1d6 cold damage. All terrain is considered difficult during a hailstorm.
4)      Crystal Storm: Snow and lightning fill the skies. When lightning strikes, it leaves behind forked crystal pillars. There is a 1 in 8 chance per exploration turn that either a character is struck by lightning causing 8d6 electrical damage or a pillar shatters near the party doing 2d6 slashing damage.

That's enough, right? But for me, I like to make some notes about what each of the things means. The temperature ranges aren't exact, they should fluctuate 10º-15º towards the most recent temperature. They are the approximation of the temperature including wind chill and other factors. There are 4 temperature bands:

Cold 40º-0º
Frigid 0º- -20º
Freezing -20º - -40º
Gelid -40º or lower

Each requires a increased level of winter protection.

So for calculating weather the first week of Jofas, I begin generating numbers. I start with 1d4. I have a paper calendar so I just note the weather at the top of the day's box, along with the mechanical effects. What are the mechanical effects? You should make something up that seems appropriate. The numerical result is in parenthesis at the start of the line, die result first.

(3) Jofas, 1st of Toil: is Clear & Windy 10º
(1+3) Jofas, 2nd of Toil: is Clear & Crisp 0º
(6+3) Jofas, 3rd of Toil: is Freezing & Windy -15º
(1+2) Jofas, 4th of Toil: is Clear & Windy 10º
(4+3) Jofas, Halfrest: is Bitter & Windy -10º
(3) Jofas, 6th of Toil: is Clear & Windy 5º
(2+3) Jofas, 7th of Toil: is Clear & Cold -10º
(4+2) Jofas, 8th of Toil: is Cloudy & Cold -20º
(1+12) Jofas, Counting: is Light Snowfall 0º
(3) Jofas, Rest: is Clear & Windy 10º

It took about 90 minutes to design the table, and about 6 minutes to  generate a week of results. As expected, there are streaks of similar temperature. On Jofas 8th of Toil there was a potential for a storm, but it passed. I adjusted the temperatures each day towards the mean of the previous day. 

Perdition is out! Grab your copy today!


  1. Rereading this, it seems like a lot of useless data, until you remember at the table that each of those things is much more meaningful to the players at the time. To the players, Clear & Windy 10 degrees is a lot different than Heavy Snowfall 0 degrees.

  2. Not to toot my own horn (too loudly), but I automated the random weather tables from the AD&D Wilderness Survival Guide at http://www.dwarvenautomata.com/random-weather-generator/. It generates a month of weather in a few seconds divided out by geographic region with options to select climate region.

  3. I agree. Very nice. I added a weather generation table to the sheet I use to keep track of time, xp awards, etc. Either way works very well.

  4. "There used to be a delightful naturalistic weather generating website that has since fallen off the Internet," he said, unhelpfully.

    I recorded a year of weather for a fantasy-European climate in the Referee's Companion of Treasure Hunters. Additionally, there's a simplistic weather generation tool similar to yours in Chapter 5 of the same book.

    For the purposes of verisimilitude, a calendar and weather are absolutely necessary.

  5. Random weather tables is something I've been interested in for a long time (30+ years). I like what you've done. That's an elegant method of getting weather persistence, gradual change, and recognizable patterns of change. I linked to and commented on your post over on my blog.


  6. The problem I see with your weather table (one I had with mine, too) is that it will tend to take weather from mild to cold and snowing, and then stabilize at cold and snowing.

    1. Well, since cold and snowing is the desired baseline, I'd say it's working well.

      The weather table is for The Frigid Realm of Exquisite Stasis named Etah-naris of Peitharchia, the Child Czar of Equilibrium.

  7. I was boggling at those temperatures until I realised they were (presumably?) supposed to be in degrees Fahrenheit.


Related Posts Plugin for WordPress, Blogger...