Garweeze Wurld Moon & Weather Generator
I use Garweeze Wurld as my campaign world because, quite frankly, I like the amount of detail that has been published....and probably just as important, what hasn't been published. Garweeze Wurld was the game world of Jolly Blackburn and the default setting for Kenzer & Company's 4th Edition of HackMaster.
Years ago Jolly published in Knights of the Dinner Table a guide to calculating the different moon's position for any date. I made this Excel sheet and used it for years before being told it was "wrong". Evidently the directions printed in KoDT were off, but screw it....I've already done the calculations....multiple times. The thing is that a worksheet that calculates just the moon's positions is of limited usefulness. Using some of the information from the 4th Edition GameMaster's Guide I made up some figures for calculating the albedos of the moons, factoring in their size and making a hip-shot guesstimation for how much light they send back.
OK, so know I can calculate how much moonslight comes back to the surface. Next I figured I should see if the light is trending up or down (i.e. Is it brighter than it was last night?) and know when the light is at a low or high point (the bottom or top 15% of the range). My reasoning is that certain creatures might be even more active at those points. It also helps to know if the brightness is above the halfway mark since I have a home rule reducing the penalties for fighting in darkness.
My next step to tweak the usefulness is to make some additional weather calculations. I picked an appropriate Earth analog for the weather, which is Munich, Germany. Using historical averages I charted out 394 days of highs, lows, rain, and wind. The start was adding a "Julien" calendar to my own, going up to 394 and then made a calculation to equivocate a real-world date to the Garweeze Wurld Julien date. This was a calculation, not a thing where I dump in some dates.
Now I have a huge array of 394 days and average weather.
Rain was interesting because the "average" precipitation is really the average of those days where it rained...I started with the exact same process and then started tweaking the numbers until I got average rainfalls that mirrored, or at least was "close enough" to the historical results. My biggest problem were just making the results appear the way I thought was most useful.
Wind and wind gusts were more of the same, but I had to factor in instances where the gusts might end up being less than regular wind speed. A formula or two and that was fixed.
Now each time you update something on the page you'll get a year's worth of weather. That's great, as long as you want to equivocate your game area to Munich. Adding in a couple of adjustment blocks for weather and precipitation and then updating all of the formulas was the answer. All you need to do is pick a real-world analog for your campaign area and compare the difference in average temperatures and rainfall. The rain adjustment is listed as a percentage.
Obviously this whole thing is not extremely useful to you if you don't use Garweeze Wurld, but might prove as some sort of template if you do have a custom game world and/or calendar. You can download the file here, or click on the lead-in graphic to get the file.