So. You’re all ready to run your shiny new campaign. You’ve spent months drawing maps, stocking dungeons, detailing noble lineages, and naming taverns. You know the name and demeanor of every NPC within a twenty mile radius of your starting town and exactly how many copper pieces the goblins in room 12 of the Caverns of Carnage are carrying in their filthy belt pouches. You’re at the table and your players are finishing up some last minute equipment purchases when one of them looks at the equipment list and sees “winter blanket.” He looks at you and asks “Will I need one of those?”
If the adventure is taking place in the Blizzard Peaks then the answer to the above question is probably obvious, and weather conditions were likely a factor when it came to adventure design. Most of the time, however, it seems like weather is an afterthought, and conditions in the outside world are perpetually sunny and mild. This may be fine for one-off adventures or rather small campaigns, or if your adventure takes place in San Francisco, but otherwise some thought should be given to climate, seasons, and the day to day weather conditions. This small detail helps reinforce the idea that the characters exist in a real world, that in turn exists beyond them and their actions. If it only rains when zombies are rising from the grave or some mad scientist is animating an abominable monster, your players will soon realize this and begin to see the weather as little more than the plot device that it is (Gee, it’s raining, I guess that means he wants us to seek shelter and get into some misadventures in a cave or something…).
My solution to handling this detail is simple: get a calendar! You could either print one off from your computer or go to the local dollar store and pick one up, if you don’t mind having kittens, lighthouses, or some similar theme (mine is Spiderman). Bonus points if you find one that tracks the phases of the moon. If you are feeling more ambitious, or if your campaign world has an odd number of days in the week, you could make your own calendar with a word processor or spreadsheet program with little or no effort. Once you have decided what day and month your campaign begins on, you can start populating your calendar squares with weather conditions and other notes (more on that later). For weather, I use a nice program that I downloaded several thousand years ago that no longer looks to be available. It accounts for climate, season, precipitation, wind speed/direction, and moon phases, and is perfect for what I need. After a bit of digging, I found this online weather generator that accomplishes exactly the same tasks. It also has the added benefit of allowing the user to customize the number of days in the week and month. After setting your parameters, one click will generate three months of weather conditions (EDIT: Charles Aikins over at Dyvers had another awesome weather suggestion, which was to use a Farmer's Almanac to "generate" your weather). Write these down in the squares on your calendar for as far out as you feel like (I usually do at least a month). Feel free to make alterations to the temperatures and rainfall amounts at this time, or even on the fly. You are by no means forced to use these weather conditions, so it can still rain when those zombies march on the town or be clear and sunny on the day of a large military engagement. This information is there for days when the weather conditions aren’t significant for any reason other than the fact that your characters are out there trudging around in it. Knowing what the weather is going to be tomorrow or next week may also give that guy who is proficient in weather sense or the like a chance to use his skills in a meaningful way.
Another benefit to the above generator or certain calendars is moon phases. This information can be important in adjudicating night time encounters, for certain religious observances, or for putting some forethought into when that werewolf is going to attack. Sticking to these moon phases can help thwart continuity issues (So there was a full moon and a werewolf attack in the village last night? Wasn’t there a full moon last week when those zombies attacked? Can my character move to a village where that type of thing doesn’t happen on a weekly basis?) and in general help establish a sense of verisimilitude.
Aside from weather and moon phases, keeping a calendar has a host of other advantages. You can write down when important events are going to take place or did take place, and when certain effects end or begin (yeah…do you remember last week when you got bit by all those rats and felt fine? Well this morning your not feeling so well…). You can keep track of character birthdays as well as making notations for holidays, feast days, religious observances, or anything else that happens in a relatively fixed and predictable time frame. Tracking things in this way gives you an at-a-glance overview of when significant events happened or are scheduled to happen in your campaign world, and helps establish a solid chronological record of your campaign. The best part? This type of calendar takes almost no effort to prepare, and can actually help you with some of the other preparatory and planning work that goes into being a dungeon master.