March 21, 2002 March 21, 2002
Weather Generation
The original World of Greyhawk boxed set contained rules for weather generation in the Flannaes. Although a little crude in certain aspects, I've found it very convenient and simple to use, with sufficent complexity to satisfy most detail-obsessed DM's. The rules require a little tweaking in order to generate realistic weather, especially for the extreme lattitudes, but otherwise are quite acceptable.
Since the product has been discontinued, and is (as far as I know) currently unavailable for purchase, I don't think anyone will mind too much if I reproduce some of the material here. Nevertheless, much of the stuff you see below is still technically ©copyright 1983 TSR, Inc.
To begin, let me start with the calendar used in the World of Greyhawk, listing the months of the four seasons and the names given to these by the various peoples in the Flannaes:
Months, Festivals and Seasons Common Olven Nomads Season Needfest Fireseek Diamondice Tiger Winter Readying Yellowillow Bear Spring Coldeven Snowflowers Lion Spring Growfest Planting Blossoms Frog Low Summer Flocktime Violets Turtle Low Summer Wealsun Berrytime Fox Low Summer Richfest Midsummer Reaping Goldfields Snake High Summer Goodmonth Sunflowers Boar High Summer Harvester Fruitfall Squirrel High Summer Brewfest Patchwall Brightleaf Hare Autumn Ready'reat Tinklingice Hawk Autumn Sunsebb Lacysnows Wolf Winter
(I realise that the elvish names for the months are a little silly, but I've included them anyway for the sake of completeness. I don't use them in my campaigns, as I make up my own words for elvish names based on the works of J.R.R.Tolkien. The appendices in The Silmarillion are especially useful in that regard.)
A couple of notes concerning the calendar:
- Each month has 28 days, and each festival is seven days long, so there are 364 days in the year.
- The months are based on the Great Moon (Luna), which waxes and wanes in cycles of 28 days. The Handmaiden (Celene), a small aquamarine moon, waxes and wanes four times in the year, becoming full during the four festivals.
- The prevailing winds are from the Northeast in Winter and Autumn, and from the East and Southeast in Spring and Summer.
- There are exactly four weeks in each month, and seven days in the week. The Flan standard week has the following days:
Starday Work Sunday Work Moonday Work Godsday Worship Waterday Work Earthday Work Freeday Rest
Next, to calculate daily temperatures, cloud cover and chance of precipitation for each month, refer to the baseline data chart below:
Baseline Data Chart Fireseek Readying Coldeven Planting Flocktime Wealsun Base temp.: 32 34 42 52 63 71 Daily high adj. +d10 +d6+4 +d8+4 +d10+6 +d10+6 +d8+8 Daily low adj. -d20 -(d10+4) -(d10+4) -(d8+4) -(d10+6) -(d6+6) Sky conditions: Clear 01-23 01-25 01-27 01-20 01-20 01-20 Partly Cloudy 24-50 26-50 28-54 21-55 21-53 21-60 Cloudy 51-00 51-00 55-00 56-00 54-00 61-00 Chance of precip.: 46% 40% 44% 42% 42% 36% Mid-month time of: Sunrise (a.m.) 7:21 6:55 6:12 5:24 4:45 4:32 Sunset (p.m.) 5:01 5:36 6:09 6:39 7:10 7:32 Reaping Good-month Harvester Patchwall Ready'reat Sunsebb Base temp.: 77 75 68 57 46 33 Daily high adj. +d6+4 +d4+6 +d8+6 +d10+5 +d10+6 +d8+5 Daily low adj. -(d6+6) -(d6+6) -(d8+6) -(d10+5) -(d10+4) -d20 Sky conditions: Clear 01-22 01-25 01-33 01-35 01-20 01-25 Partly Cloudy 23-62 26-60 34-54 36-60 21-50 26-50 Cloudy 63-00 61-00 55-00 61-00 51-00 51-00 Chance of precip.: 33% 33% 33% 36% 40% 43% Mid-month time of: Sunrise (a.m.) 4:45 5:13 5:42 6:12 6:46 7:19 Sunset (p.m.) 7:29 6:57 6:10 5:21 4:45 4:36
Once you've rolled the temperature and cloud cover, you need to check the chance of precipitation. If there is to be precipitation, you'll need to consult the following table to determine the type and duration of the precipitation:
Precipitation Occurence Table Dice
rollType of weather Temp. required (°F.)
Min. Max.Chance of
continuingChance of
rainbowNot
allowed in:01-02 Blizzard, heavy - 10 5% - Desert 03-05 Blizzard - 20 10% - Desert 06-10 Snowstorm, heavy - 25 20% - - 11-20 Snowstorm, light - 35 25% 1% - 21-25 Sleetstorm - 35 20% - - 26-27 Hailstorm - 65 10% - Desert, dust 28-30 Fog, heavy 20 60 25% 1% Desert, dust 31-38 Fog, light 30 70 30% 3% Desert 39-40 Mist 30 - 15% 10% - 41-45 Drizzle 25 - 20% 5% - 46-60 Rainstorm, light 25 - 45% 15% - 61-70 Rainstorm, heavy 25 - 30% 20% - 71-84 Thunderstorm 30 - 15% 20% - 85-89 Tropical storm 40 - 20% 10% Desert, plains 90-94 Monsoon 55 - 30% 5% Desert, dust, plains 95-97 Gale 40 - 15% 10% Desert 98-99 Hurricane or typhoon 55 - 20% 5% Desert, dust 00 Special - - 1% - -
(For the "Special" precipitation category, you'll need to refer to the Terrain Table to determine type. If there is no continuation of the special precipitation, you should roll a new form of precipitation.)
The remainder of this page is still under construction. If you have any queries or comments, email me at <mgeilon@oocities.com>