Weather Generator, Part 3: Climate Templates

Illustration from "Weather in the World of Greyhawk" from The Dragon #68

Previous posts:

Part 1, here.

Part 2, here.

Download the Weather Generator, here.

Today, we'll look at the second tab or sheet from the left - Climate Templates.

For each climate zone you create, you'll start with one of the twelve pre-set climate templates contained in this tab. 

Three important things to note:

1. While there are only twelve templates (I haven't yet built in any slots for additional ones), each can be tweaked, modified or completely redesigned from scratch by the user.

2. The templates are templates, nothing more. You can still individually adjust most things within each particular climate zone. For example, you can use the same Desert template for two different climate zones in different latitudes. In one, you can lower the average temperature by 20 degrees. In another, you can increase the precipitation chances from 5% to 15%. And so on.

3. I tried to set up the templates to be "realistic" (working off initial numbers presented in The Dragon 137), so you don't need to change anything. Of course, your world may be quite different from Earth, or you may think I'm just wrong about the length of desert seasons (which is quite possible) or whatever. In that case, change it! 

Each template is actually quite simple, containing three sets of information:

1. The timing and duration of seasons. Does "Summer" in north temperate coastal areas last from June through September or merely July to August? And so on.

2. Each month's precipitation chances. This is roughly the chance per day that there will be a precipitation event. Again, you can change the numbers here, or you can wait to further tweak them in a general way for a particular climate zone. For example, if Tropics I (Coastal with Rainy Season) has 10% precipitation for seven months and 85% precipitation for the remaining five months, in your own "Super Monsoon" zone, you can change it to 20%/95%.

3. For each season, what is the range of temperatures? You read the numbers this way: If the range for Fall/Spring of Tropics I in the 96-00 category is 110 to 120, that means there's a 5% chance per day that the temperature will be within the upper range of 110 to 120 degrees Fahrenheit.

Here is an example of one climate template:

And here is the full list:

1. Tropics I (Coastal with Rainy Season)
2. Tropics II (Inland Swamp or Jungle)
3. Tropics III (Savanna, etc.)
4. Tropics IV (Desert)
5. South Temperate I (Coastal Warm and Rainy)
6. South Temperate II (Coastal Hot)
7. South Temperate III (Southern Steppes)
8. South Temperate IV (Forest, Hills or Mountains)
9. North Temperate I (Coastal)
10. North Temperate II (Inland)
11. Polar I (Coastal)
12. Polar II (Inland)

There are four Latitude zones - 0-25º, 25-50º, 50-70º and 70-90º. Each has at the least, a coastal climate zone and an inland climate zone. But the two southern most Latitude zones each have two additional zones.

Seasons vary less the closer one gets to the Equator. On the other hand, there are more geographic climate options.

The original templates (and my tweaks) are probably more European than American. I've lived in Boston, Chicago and London. Boston and Chicago are actually 10 degrees south of London. But Boston and Chicago get colder. Indeed, they also get warmer.

So, if you want "American" values as opposed to "European," make the winters colder and the summers hotter. In this regard, Asia (or at least the Asian Eastern coast), may be even more American than America. 

Cheers, weather nerds!

Tomorrow, the Climate Zones themselves.      

Weather Generator, Part 2: Weather Parameters

Illustration from "Weathering the Storms" in The Dragon 137

I made some general comments in Part 1, yesterday.

If you haven't downloaded the Weather Generator Excel Workbook and would like to, you can find it here.

Okay, let's look at the first tab on the left, WEATHER PARAMETERS.

The red values can be changed. The black values aren't locked, but you don't want to change them. Or, rather, in most cases nothing would really happen if you did - they're just default reminders.

However, for the reds, in every case, you don't need to change anything, but may simply leave the red values untouched. I would actually recommend this.

I. Choose Game System

This is self-explanatory. For the moment it has no effect. It's in there for when I build movement rates for different game systems into the Calendar.

II. Choose Hex Size and Base Move (if applicable)

Ditto.

III. Choose Precipitation Event Name

I'm not sure why anyone would want to change these, but if you want to change "HEAVY BLIZZARD" into "STRONG BLIZZARD" or whatever, you can.

Now that I think of it, I suppose one reason might be to change the names into those of another language.

IV. Choose Relative Chance of Events

Two things to note:

1. These are the general defaults. You can (and almost certainly will want to) change them within particular climate climate zones. But if for some reason you think the default for DRIZZLE should always be twice as likely as LIGHT RAINSTORM, go ahead and increase the DRIZZLE % or decrease the LIGHT RAINSTORM %.  Again, they don't have to add up to 100%.

2. These apply only within possible temperature ranges. For example, if the temperature is -10 degrees, whatever value you have put in for DOWNPOUR, it's not going to happen.

V. Minimum and Maximum Temperatures for Events

You can't change these (if you do edit the black, nothing will happen). This section is there in part to illustrate how the algorithm works.

VI. Choose Duration of Events

These cannot be changed within the particular climate zones. So if you want to change them, you're only chance is now. The durations are intended to be "realistic," but I might have been wrong about them, and in the end it's your call. If you want sleet storms to last an average of two weeks in your world, go for it.

VII. Choose Chance of Events Continuing

This is similar to, but not quite the same as VI. Sleet storms last 1d6 hours but then have a 20% chance of continuing for another 1d6 hours (and then have a 20% chance of continuing for another 1d6 hours...). You can change that.

VIII. Choose Wind Speed of Events

Here also, this is your only chance, as these are not adjustable within the climate zones. If you think I've overestimated the power of Gales, change it.

IX. Choose Precipitation Amount (per hour)

You can change the average precipitation amounts and/or the average variance of them. The variance mechanic adds or subtracts a percentage up to 100%. So "+/-90%" means the inches of rain per hour could be anything from 10% to 190% of the average. 

X. Choose Chance of Lightning

The Dragon 68 article has a mechanic where whenever there is lightning, you have a small chance of being hit by it, and if you are, you take some ridiculous amount of damage. Though the chance is small, given enough chances, you will be hit.

In my view, that mechanic is insane. It implies that any low-level party that attempts a long-term wilderness trek will almost certainly be electrocuted.

I would dispense with that mechanic.

For me, the main purpose of lightning is to decide when spell casters can cast a Call Lightning spell. It's an extremely powerful spell, especially for its level, so you want lightning to be somewhat rare, but not so rare such that the spell will be meaningless.

Also, lightning adds atmosphere.

You can also change the lightning frequencies within particular climate zones. This only changes the recommended default. It actually makes perfect sense that some zones - those nearer to the equator, "evil" zones and so on - would have much more lightning than others.

Keep in mind that the chances are per 12 hour period. So, for example, if there's a 25% chance of lightning during each half-day of TORRENTIAL RAINS, it's highly likely you'll get a number of lightning episodes in, say, a two-week storm. 

XI. Choose Chance of Rainbow

Okay, it sounds silly, but rainbows can be fun (I know, I know). Single, or especially double or triple rainbows might be omens. In extreme cases, you can actually see storm gods in he sky. Each precipitation event has a separate chance of ending in some type of rainbow. Change these if you want. 

XII. Choose Chances for Type of Rainbow

If you want every rainbow to be a literal physical bridge to Valhalla (a Bifrost bridge), go for it.

XIII. Choose names and Chances for Cloud Cover

All the sources I've seen have percentages that track the given defaults. But if you think, say, that Very Cloudy days are too common, change it. You should know, however, that I have modified these chances in my algorithm for each climate template. For example, in areas of low precipitation, there's more than a 25% chance of it being Clear. But if you want to change the chances, generally, or if you want to change the name "Very Cloudy" to "Overcast" or whatever, go for it. 

XIV. Year begins on which Phase of the Moon?

Moon phases can be important. Or not. It's obviously up to you. But if you want to change the phase your year begins on, you can. Each phase will last 30.44 days, so the phases will gradually diverge from the months.

This assumes one "earth-type" moon with the same orbit period as our moon. Unfortunately, the workbook isn't set up to change that. I might try to do so in the future.

By the way, a friend reminded me that no version of Excel includes the "Moon Phases" font. But it's easy to download and add it. (It takes about a minute.) You can find the font here.  

XV. Choose Other Modifiers

Most of these you can also change within particular climate zones, and some will also be affected by terrain, but you can also change them generally here.

Base wind variance/maximum: If there is no precipitation event, the default wind speed will vary from 0 to 15 mph. You can change that. Increasing or decreasing it will also increase or decrease the variance for when there is a precipitation events.

Overall wind speed modifier: If you simply want your entire world to have a windier (or less windy) default, go for it.

Overall temperature modifier: Ditto for temperature.

Overall precipitation modifier: Ditto for precipitation.

Rainbow chance multiple: Change those general rainbow chances, you rainbow unicorn. Or not.

Precipitation duration multiple: Maybe you think every rainstorm, snowstorm and hailstorm should last longer.

Temperature consistency: This is an interesting one. The algorithm assumes that temperatures will vary within a range (given by the climate zone and season) from day to day, but the temperature consistency percentage represents the chance per day that it won't vary by that much (it will still vary by a little bit). Thus, you get longer lasting "heat waves" or "cold waves." You can adjust this.

Cloud cover consistency: same idea.

By the way, I'm not a weather nerd. I did a fair amount of research for this but some questions I still don't really know the answer to. For example, do clear days cluster?

Temperature drop variances: In almost every climate and in every season, the temperature drops in the evening. You can modify the possibilities here. It's probably more important to modify which possibility you get in a particular climate zone. But you can change the general parameters here if you like.

******

That's all for now. Tomorrow, Climate Templates!    

Weather Generator, Part 1: Introduction

Illustration from "Weather in the World of Greyhawk" from The Dragon #68

In writing Book of Fiends, I decided to add some "additional" spells - many of them originally Druid spells from Eldritch Wizardry. Since some of these spells involve weather and have little meaning without some sort of campaign weather system, I started to think about designing or at least adapting a weather generation system for Seven Voyages of Zylarthen/OD&D.

The systems I found fell into three basic categories:

1. Simple. I would put, say, the Delving Deeper system into this category. Saying it's simple is not a criticism. Indeed, I think the Delving Deeper system is the best out there. For a system generated with dice, it must be simple in order to be playable. The problem, of course, is if you think simple is, well, too simple.
2. Complex. The Dragon 68 and The Dragon 137 put forward realistic and satisfying weather generation systems. As I understand it, the scheme in issue 68 was later incorporated into the Greyhawk Boxed Set campaign setting. The problem here is that I just can't see how these systems are really playable. Just to calculate the weather for one day in one climate zone requires many die rolls. Doing so would either slow down play or require a huge amount of boring prep work for the referee. An the thing about weather is while it might be very relevant to play, it's more often not very relevant. You don't want to take ten die rolls to discover that it's partly cloudy with a high of 72 degrees and a gentle breeze.
3. Computer generated. There are a number of sites where you can ask for one day's weather (or in one case a week's worth of weather). Sometimes you can change the climate parameters and sometimes you can't. But I find the computer dependent snapshot approach unsatisfying. It's usually only a snapshot, and frankly, I don't want a system where you have to keep visiting a website. It's not very 1974.   

In response to these alternatives, I decided to design an Excel workbook for instantly calculating 365 days worth of weather for as many different climate zones as you want.

I'm not computer programmer but I've always liked Excel and do a fair amount of work with it in my profession.  

The idea is, once you do a small amount of prep-work - basically deciding what your climate zones are going to be and whether there will be any variation from the basic templates - you can calculate all of your world's weather at the touch of a button. You can then save it a PDF or set of PDF's and either print them out or save them on your tablet or phone.

It's complex, but the complexity is already baked into the system for you.

The worksheet incorporates ideas from those two issues of The Dragon plus some ideas and tweaks of my own.

In the next few posts, I'll be explaining how to use the workbook. You can download the BETA here.

It's a BETA because I want to put more things into it. Among other things I want it to display movement rates. (You want to keep marching cross country through a blizzard? Fine, but you move at 3 instead of 12, or whatever) But before I do that, I need to finalize my thoughts on Zylarthen/OD&D wilderness movement.

The BETA includes 4 worksheets in Caps: WEATHER PARAMETERS, CLIMATE TEMPLATES, CLIMATE ZONES and CAMPAIGN CALENDAR.

CAMPAIGN CALENDAR is where you get your results. I've already set it up with 19 pre-set climate zones that track this Zylarthen/OD&D campaign map. So you literally can use it as is.

But if you want to tailor it to your world, you can pretty quickly do so by making adjustments in the first three sheets.

The workbook makes heavy use of random functions. If you're familiar with Excel, you know that by simply changing 1 cell (typing 1 into any blank cell or whatever), every random function will recalculate. This is how you generate weather for different zones. Or you can simply recalculate a year's worth of weather if you don't like what you got. Or you can sit there like a weather nerd and waste an hour seeing all the different sorts of weather patterns that are possible for an equatorial monsoon zone, or whatever.

You can also turn off the recalculation function or, of course, save one of the results to a separate workbook (saving values not formulas) or by saving to a PDF.

The cells in red are what you might want to change. You don't want to touch the cells in black unless you want to experiment with changing the entire workbook. Most of the red cells are framed by a black "default" cell, giving you a "recommended" setting or range of settings.

There are 3 worksheets in non-caps: Calendar Data, Random and Movement. You don't want to touch these, although you can.

It's all up to you. I haven't locked anything.  However, keep in mind that some of the formulas are extremely complex. If you alter something in black, especially in the Calendar Data sheet, you might screw everything up and not know how to get it back.

I suppose if you do want to fool around with the "guts," you want to save an original copy first.

See, you can play God but playing Meta-God is problematic.

Again, the worksheet may be downloaded here. I'll be explaining how to use it over the next few posts, but you're halfway familiar with Excel, you might be able to figure it out on your own.

For now, here's the map that I based the climate zones on. It's from a post I wrote two years ago:

And here are some sample months from four of the zones.

• # means there's lightning.
• "x in rain" means the entire storm, yields, yes, x inches of rain.
• Stars and crosses are rainbows. You can get anything from a normal "single" rainbow to a bridge to Valhalla. But to get that rare bridge you might have sit there, generating new zones for a while.

1. A stormy August in the Great Coastal City:

2. It doesn't rain much in the desert, but sometimes lightning strikes from a clear sky. Also, the temperatures drop precipitously at night:

3. The rainy season in the Great Jungle:

4. Winter in the Tundra:

I hope you find the Weather Generator interesting and useful. And I look forward to improving it. As always, feedback is welcome and appreciated.

Enjoy!

Notes on Wilderness Movement

The wilderness is problematic 

I'm currently putting the finishing touches on Book of Fiends, a Seven Voyages of Zylarthen/OD&D reimagining of the Fiend Folio. Among other things, it's going to have some great art.

In the process of working on it, I've been diverted into also exploring some other paths. Book of Fiends will include a number of "additional" spells - OD&D spells not included in the original Zylarthen.

Many of these spells were originally "Druid" spells from Eldritch Wizardry. Since some of these concerned weather, I've been rethinking weather rules and designing an Excel spreadsheet to calculate the weather.

In turn, since weather can sometimes affect movement, this got me to think (or rethink) wilderness movement rules.

Here are some propositions/proposals:

1. In virtually all of the old school iterations of D&D as well as the clones, the value of horses for long-distance wilderness movement has been overestimated. In all of these systems (including Zylarthen) horses move at up to double or even triple the speed of men. This is unrealistic. Over long distances, men move about as fast as horses. You can impel a horse to move faster for a day or two but then you'll have to rest it. So, if you're doing, say a week or a month long trek through the wilderness (where you can't switch horses at the next Pony Express stop), a horse isn't going to help you that much.

2. Extra encumbrance doesn't detract from long-distance movement as much as it does from short-distance movement. Soldiers have been marching with heavy packs since long before the middle ages. If they weren't wearing heavy packs they would be faster, but not that much faster. Marching with heavy packs is what soldiers do. And if they can do it, adventurers should also be able to do it. So, systems that base wilderness movement on short distance movement (based on encumbrance) are underestimating wilderness movement.

3. For the above two reasons, all wilderness movement through clear terrain should have the same base value - perhaps 15 to 20 miles a day. Various things could give bonuses or penalties. For example  if you have a certain type of horse, then you can double movement for one to three days as long as you rest it for one to three days. If you're unencumbered or lightly encumbered, you get a +1 or +2 on movement. Mules get a bonus over harsh terrain. And so on. But the base move stays the same, subject to terrain.

4. Having just one base move (with possible bonuses/penalties) is also preferable for reasons of simplicity.

5. If you're going to have weather events affect movement, keep in mind that weather might be already implicitly "baked in" to some terrain modifiers. So, for example, you move slower in mountains partially because of storms and the wind. You move slower in deserts because of the heat. Jungles are daunting, partially because of the frequent torrential rains, etc. If you want to have weather affect movement, then you might need to scale back on some movement penalties due to terrain itself.

6. You can make an interesting game out of fractional movement speeds. If you have a map with 30 mile hexes and the base move of the party is, say, 20, then instead of decreeing that the party moves 2/3 of a hex each day (and making little dots on your map), have them roll a 13 or better (2/3 of 20) each day on a twenty-sided die. Success means they leave the hex. Failure means they stay. This inserts a bit of chance and die-rolling drama into wilderness movement. And of course, for every day that they stay in the wilderness, they make one or two more wandering monster checks. Let the players roll them... They will want to get out of the wilderness as quickly as possible!

Criticism, comments or advice would be appreciated. Cheers!