Weather Generator?


I've been wanting to generate weather that makes sense over a long period of time, so I don't get the "it's hot! now it's cold! now there's a tornado!" sort of weather most generators seem to supply. I'm thinking one that supplies temperature, precipitation, cloud cover and wind conditions over a period of 12 30-day months, with seasonal and climate variations. Does anyone have a link to a reasonable generator like that which doesn't require much work to use? A lot to ask I know, but I can hope! ;)

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First Post
I have a couple of weather generators that I have used in the past but none have ever been able to exactly simulate the evolving weather patterns that you're looking for.

What I do is go on line and look for a real world locale that approximates the area and climate that I want to simulate. Use their weather logs as the weather pattern for that area. Check the NOAA site. They have links to historical weather for most parts of the world.


Victoria Rules
'Bout the only thing most random weather generators are any good for is determining the weather on the very first day of your campaign. After that, you're better off just rolling some dice (skewing the odds towards normality for the season and location) to see how it's trending from yesterday.

So, if it's midsummer in a typical temperate climate and your random generator gives "heavy rain, windy, very cold" on Day 1, then for Day 2 you'd roll d% for each condition:

1. pretty much anything less than 99% means the rain has at least eased off; less than about 80% means the rain has stopped; less than 60% means the sun has partly come out; and less than 40% means it's sunny;
2. same for wind...the average summer day has at least *some* breeze, so your median roll wants to indicate a light breeze; to continue yesterday's "windy" you'd need over 90%, and it'd take about 97% to increase to "very windy";
3. much the same as above; skew wildly toward normal and only allow an extreme roll to enhance or continue the unusual weather.

That said, if the mood you're trying to set demands a thunderstorm, then there's a thunderstorm. :)

Lane-"the climatology I studied in college has to be useful for something"-fan


I once tried to create a weather generator that worked by adjusting the previous temperature, but what I discovered was that it was really easy for you to have a run of luck and end up with 'global warming' or 'global cooling'. Even with dampening modifiers on the dice roll based on departure from average temperature, I was never happy with the result.

My suggestion for generating weather would be pick a city with a climate similar to the one you want to simulate, and then go to online weather site (, for example) and look up its historical temperatures for a suitably long period. Or simply record the weather it experiences for the week you are planning the session.

In my experience, it's not a good idea to generate random weather on a daily basis. Instead, pregenerate (by whatever method) a couple weeks worth of weather. Likewise, pregenerate your 'random encounters' (if you want any) and spend some time thinking about how you want to handle them. Minimize the amount of on the fly dice rolling and creation you have to do. You'll always find yourself improvising the unexpected, but try to handle the expected before the last minute.


First Post
The Greyhawk box set had a sweet weather generator in the glossography. (Accounting for latitudes and all that.) Don't know if we ever cause to use it...

"Climate is what you expect, weather is what you get." - Robert A. Heinlein

I like to to decide on climate and then just either choose or randomize the weather slightly off a norm. I feel that the weather, like major villains, should only manifest in the extreme based on a conscious choice by the DM (because the DM is the one who has to deal with it the most).


First Post
No need for a Weather Generator, if you take a particular look at Climate.

Think of Climate as an Endless War between Good and Evil, only in this case, Hot and Cold.
This war, instead of progressing slowly, progresses rapidly and annoyingly, with one Battle Front coming through after another, every few days. (The term 'Front', ala Warm Front or Cold Front, was taken from a Real World War and it's fronts.)

So, it turns cold. Then hot. Then cold. Then hot. Then colder. Then hotter. Then less cold. Then less hot. In mad succession, never ending.
Each front brings storms of wind and rain, followed by gusty winds, followed by partly cloudy weather or sunny weather. Occasionally, a slow moving or nearly stationary front brings a long period of storms and rain.

If it is summer, these storms are rain storms.
If it is winter, these storms are snow storms (or, occasionally, ice storms or sleet storms.)
If it is spring or autumn, the storms could be of any kind.

If the storms are gentle, light rain or snow falls.
If the storms are heavy, thunderstorms or thundersnow occurs.
If the storms are strong, severe thunderstorms and tornadoes, or very deep snow and blizzard conditions, occur.

Now ...

There is always some Clown out there, in the D&D multiverse, who thinks he should be the guy running the weather, and not the weather.
Or the druids decide they are going to get revenge for the latest attack on their forest.
Or the elementals were let into the world, and they want to show off.
Or the efreeti decide to heat things up a bit.
Or the lich decides winter would be more appropriate (even they it is still July.)

Counterforces move to try to correct the weather imbalance, which of course stokes more magical interference in the weather ... the chain reaction of this can lead to some pretty serious problems worldwide.

I mean, even in the Real World, the weather is unpredictable and downright freakish at times. Throw in magic and rabble rousers, and the occasional troublemaker, and a lot of faerie and elemental forces that want to have it their way, and counterforces, and just about anything you want could happen.

Hurricanes normally occur over warm water of 80 degrees or higher (27 celsius or higher.) Normally, they begin over areas where the weather is (paradoxically) tranquil and calm, down in the tropics.
Once started, they - much like bulls - rush along, mowing everything down in their path.
Since hurricanes are such enormous weather systems, affecting in some cases more than one million square miles of surface area in one way or another, they can throw side effects into regions thousands of miles from themselves.
Fooling around with hurricanes using magic is ... well ... dangerous. It is much like trying to control a raging forest fire with a garden hose. Unless you've got some pretty powerful magic, you may unleash something you never intended, playing around with such forces.

There are some campaigns where the weather is artificially generated by resident faerie beings or wizards, and one of them is the Flanaess region of Oerth (Greyhawk.)
There, the climate is warm temperate or subtropical from Veluna and northern Furyondy, east through the Shieldlands, to northern Nyrond and the Theocracy of the Pale, across the mountains to Ratik, and offshore to a point well north of the Lendore Isles.
West of the Crystalmists, the climate is subtropical all the way to the ocean north of Zeif, and warm temperate up through Tusmit.
*North* of this line, the climate turns from warm temperate to subarctic within a hundred miles, except only in Perrenland which is cold temperate.

What does subarctic mean? What does it mean versus temperate?

Tropical = always summer
Subtropical = always summer, but occasional cold snaps for 4 months
Very Warm temperate = 6 months of summer (2 to 3 months of winter.)
Warm temperate = 4 months of summer, 4 months of winter.
Cold temperate = 3 months of summer, 5 months of winter.
Frigid temperate = 3 months of summer, 6 months of winter.
Subarctic = 3 months of summer, 7 to 9 months of winter.
Tundra = 2 months of (quite variable) summer, 9 to 10 months of winter.
Arctic = Always winter.

Final thing: A classic rule of thumb about the Temperate climate is that you are always importing somebody else's climate. You never really have your own (and you wish the climate from somewhere else would leave, and it does, but then you wish what replaced it would go away too, and ...)


I made a table a while back for the main area in my campaign world... I think it was loosely based on something I saw in an old MERP sourcebook long ago.

Most of the time I just used it as a general guide (just for consistency) - but I have also used it to determine one week/month from another (and if week 2 was drastically different from week 1, I would make the transition slowly over the course of a few days or so).

Here's a link to that table if you think it might be of interest (though it does have 28 days in each of its 13 months/moon cycles):

(broken link removed)

It's far from perfect, but (hopefully) it might spark a few ideas (or not :) ).

* * *

Edit: Sorry - it doesn't seem to want to link directly... but it appears on this page of my campaign website:
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Thanks for all your suggestions (and links)! I'll definitely look into them. Thanael, thanks for the generator link, it's just the sort of thing I was looking for.

If anyone knows of a more modifiable generator, maybe a downloadable one, don't hesitate to link me! ;)


Just out of curiosity, why do you need a generator?

Recently, I've been trying to make weather a more significant factor in my campaign, in part to add a sense of veracity and in part to provide another potential tactical factor to my encounters (at least, the outdoor ones) and the heroes' plans.

I thought about some sort of system to generate the weather, but ultimately decided that I didn't need it. I don't use a random generator to come up with my maps; why should I do it for the weather.

I choose the weather (within reasonable expectations) that fits the challenges or atmosphere I want for my story. In the same way that I design a map, pick out opponents, or otherwise set up elements for an encounter or segment of a story.

I recommend that route!


CharlesRyan: I'd like a generator because I have no real feel for believable weather patterns and because I'm lazy and don't want to have to keep track of it beyond checking a list in case the matter comes up in the game. If it were left up to me the weather would probably always be dry and sunny with no wind, LOL! I like the idea of random weather patterns being a factor to deal with, I just don't want to have to do the work myself.

The D&D 1e Wilderness Survival Guide seems to have the sort of thing I'd imagined, but it'd take forever to sit and determine the changes day by day, which is why a generator to do the grunt work would be welcome.


First Post
The 1e Wilderness Survival Guide. Bar-none.

I still use it to this very day. There was a generator online that actually generated the weather from the WSG for you... I don't know if it's still out there, but Google is your friend. I printed off a year for each terrain in each climate type, and I'm ready to go for life.

And I agree - "making it up" is hugely unsatisfying (both for me and my players).


First Post
Roll a d6:

1. Choose whatever weather will annoy your PCs the most.
2. Choose whatever weather will annoy your PCs the most.
3. Choose whatever weather will annoy your PCs the most.
4. Choose whatever weather will annoy your PCs the most.
5. Choose whatever weather will annoy your PCs the most.
6. Re-roll



First Post
Edena_of_Neith that was a great fun little post. I'd give you xp, but I've allotted my giving for this 24 hours.

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