Traveller 1977: Expanded World Data (Axial Tilt, Average Temperature) and Random Weather Encounters

If you are a Classic Traveller referee and have just finished generating a subsector with the procedures from Book 03 Worlds and Adventures you might be eyeballing a world or two to develop more fully.

One of the first questions I asked myself was what is the weather like on this world?” There is not a lot of referee guidance given on this subject, not until GDWs Book 06 - Scouts. The procedures in Book 06 Scouts are extremely detailed and, at least for my tastes, produce an unnecessary amount of game prep I would not use.

What do I want as a referee for game play?

  1. Are there temperature conditions that we must account for?
  2. Are there swings in seasonal weather?
  3. Are there weather conditions that might impede play?

Finally, I’d like to have this extended world data encoded using the same 0-C digit system that is familiar for the rest of the world data.

Axial Tilt

Axial tilt tells us whether a planet has extreme variations in seasons.

Roll 2d6-2:

Digit Axial Tilt & Label
0 -90%~ Extreme
1 -50%~ Extreme
2 0%~ None
3 1%~ None
4 3%~ None
5 15%~ Slight
6 20%~ Slight
7 25%~ Slight
8 30%~ Slight
9 50%~ Extreme
A 90%~ Extreme

Average Temperature

Roll 2d6-7 + atmosphere

Note: Atmosphere’s 0 and 1 would have extremely different temperatures depending on the time of day.

Digit Temperature Average °F
0 Frigid -225
1 Cold -70
2 Cold -10
3 Cool 20
4 Cool 40
5 Temperate 50
6 Temperate 60
7 Warm 80
8 Hot 110
9 Hot 160
A Searing 220
B Searing 220
C Inferno 330

If the axial tilt is none, then the temperature is consistent. If the axial tilt is slight then you can imagine that there are variations of one to two steps in either direction from the average. If the axial tilt is extreme then you have changes between three to six steps in either direction.

Random Weather Encounters

Planets possessing an atmosphere other than 0 (no atmosphere) have weather conditions.

Throw 1d6 on a 5 or 6 there is adverse weather. In cases of adverse weather, we can use a variation of the reaction throw to determine the severity of the weather event:

Apply the following DMs to the result:

Atmosphere DM
1-5 +1
8-12 -1
Size DM
5-9 -1
10-14 -2
15+ -3

Throw 2d6 - DMs:

Result Severity
2 Extreme
3-5 Major
6-8 Moderate
9-11 Minor
12 Limited

10 is an intense, violent storm. 0 is a minor, short event. To determine how long the storm lasts in minutes, throw 2d6-2 and multiply the result by 5. You’ll have to factor in the temperature, seasonal effects, and other world data to determine if it is an extreme” dust storm or a minor” rain shower. If necessary you can use the severity of the weather to apply DMs to skill throws (in a range of -4 (extreme) to 0 (limited), where limited” weather events may not directly effect skill throws but may still provide fictional constraints on actions.)

Inspiration for the random weather encounter procedures comes from Traveller’s own encounter procedures and Michael Brown’s Hazard: Storm! article in Freelance Traveller.

September 8, 2022 · Traveller · GM tools · Observation Deck


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