This entry is part 2 in the series House Rules from The Adventurer's Club


This is part 2 of a series presenting the various House Rules that have been introduced into the Pulp Campaign that I co-GM. Today I’m presenting some cold, heat, wind-chill, and altitude tables that were developed for the campaign in preparation for a midwinter race against time in the Frozen Wilds of Western Canada.

Although designed for a Pulp Campaign built with the Hero System, the rules and tables are easily adaptable to any RPG.


Credit where credit’s due

As always, Blair Ramage deserves half the credit, and half the blame, for these rules. This article is largely based on discussions between us, but was written by Mike alone. Note that the rules writeup was also done by Mike alone, after the general principles, approach, and draft rules were approved (and revised) in collaboration with Blair.


Cold and wind-chill are some of the most dangerous conditions that characters can encounter, because they trigger automatic survival responses in human physiology that make every task undertaken – even those essential to continued survival – more difficult. Adding these effects to any encounter vastly increases the danger posed by that encounter. Added to that are the psychological effects of knowing that things are harder, which should create an air of desperation to every such encounter.

And yet, every version of this sort of thing that I have seen falls short of what is necessary to actually trigger the psychological effects involved, never mind accurately reflecting the dangers posed. Frostburn, the D&D 3.0 supplement, is one of the best, but it’s not the most user-friendly system to wrap your head around.

We wanted a system that was simpler to use, but that nevertheless created the atmosphere of acute danger desired, and was a little more robust in terms of the real world. So that’s what we created.


Frostburn was the initial template, but we actually started by researching wind-chill. The actual goal was to have a table that gave us the effective temperature loss due to wind of different speeds, but we quickly found that the real-world situation was more complicated than that.

The tables already present in Champions 6th Edition were intended to be our foundatio°ns, but didn’t go far enough for our needs. So these became our second template.

Researching the subject involved gathering information from multiple sources of impeccable credibility and then trying to resolve them after we discovered that there is no consensus on the subject. Australian meteorology uses a different formula to American meteorology, for example; the US version doesn’t take into account atmospheric humidity.

The more we dug into it, the broader the subject became. We decided early on to cover high temperatures as well as cold and to make the system more universal. We also decided to extend it to cover wind speeds and temperatures that were way in excess of those that might reasonably be encountered in real life – this was for use in Pulp campaigns, possibly in superhero campaigns, and even in Fantasy campaigns, and in all three cases, larger-than-life possibilities needed to be accounted for. It’s fair to say that none of the tables went far enough for game needs.

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The Rules

So what’s in the rules?

  • Wind-chill by Air Temperature and wind speed.
  • Altitude effects
  • Humidity effects
  • Perceived Temperature & danger level
  • Game Effects:
    • Low Pressure
    • Rain/Snow
    • Extreme Cold & Heat
    • Wind Velocity
  • The STR table (for easy reference)*

* yes, this is the same one that I presented in part one of this series.

The following is a snapshot and discussion of each of these rules sections.

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Wind-chill by Air Temperature and wind speed

This is what we were initially after. Presented in two forms (one in °F, and one in °C) showing quite different information, because we weren’t sure which one would end up being most useful. As it happened, we used the °C version, but kept the °F version because it gave the frostbite times; it has no other value within the rules.

What’s missing is a table converting from °C to °F and vice-versa. Darn it. So I went looking for one to link to, and guess what? None of them go far enough. So I made one, just for our readers. You can find it to the right. You might see holes and gaps in the entries – that’s because I only converted the specific values that show up on the tables in the rules.

Using this section is fairly straightforward: you decide what the air temperature is, decide what the wind speed is, and look up the values on the tables. An Air Temperature of 5°F (-15°C) and a wind speed of 25mph (40 km/h) gives an effective temperature of -17°F (-27°C) according to the top table, which shows that characters are just out of the temperature range for Frostbite.

Note that we aren’t talking about the sort of Frostbite that gives rosy cheeks and a little discomfort; we’re talking loss of fingers, toes, noses, ears, perhaps even more substantial portions of limbs. Dangerous levels of Frostbite.

According to the lower table, the effective temperature is -27°C, which tracks with the upper table – something that’s not always the case – and rates the wind-chill-adjusted temperature as “Cold” (Blue zone), ie in the -25° to -45°C range.

Altitude effects

Temperatures also drop with altitude. I have given these in meters, and have not provided conversions, because most maps give altitudes in metric these days if not both ways.

The values determined in the previous step are sea-level values; at the top of, say, Mount Jumbo in Missoula, Montana, an altitude of 1453m (4768′), effects would be rather more pronounced. That’s a further change in temperature of between -10.1 and -10.8°C – call it -10°C for convenience. Note that you can’t look up this number to get a conversion to °F right away – you have to look up the total. Ten degrees colder than -27°C is -37°C, which the conversions table gives as -35°F. With that added altitude, we have an effective temperature change of 40°F due to altitude and wind.

Going back to the first table, locating the wind speed line and tracking across finds no entry for -35°F; -31° is in the 30-minute Frostbite Zone and -37° is in the 10-minute Frostbite Zone. Going up the column from the -37°F entry shows a -35° entry in the 30-minute zone, so conditions are right on the cusp of the 10-minute zone but aren’t quite that severe yet.

The table on the right is provided for convenience – it shows the altitudes at which a specific temperature drop occurs. This is very useful when characters are climbing mountains, especially when combined with the boundaries (eg the Frostbite indicator) on the other tables.

Humidity effects

This section shows how to correct the wind-chill adjusted temperature for humidity. There’s no value stated for -37°C, but at -35, we’re talking -2°C for every 5% humidity, so that’s close enough. If the conditions that the PCs were experiencing were, say, 40% humidity, that’s another -8°C onto the effective temperature, so we find ourselves at -45°C (-43°F). This is quite enough to shift table one’s readings solidly into the ten-minute zone, and only 5°F removed from the 5-minute zone.

It would not take much additional humidity to bridge that 5° gap – 15%, for a total of 55%, would be enough.

Perceived Temperature & danger level

Comparing the resulting effective temperature of -45°C (starting with the original wind-chill adjustment (15°C and 40km/h) and moving across the table to the right) puts us right on the edge of going from Zone blue (-41°C) into zone Purple (-48°C). Going across to the next highest value and then up the column shows -45°C to be the very edge of the zone change. If anything at all worsens, conditions will enter the extreme danger zone.

Game Effects: Low Pressure

Mount Jumbo is just below the threshold (1453m vs a threshold of 1525m); that 72m (about 236 feet) are gold, so far as the PCs are concerned.

Flying over the mountain, with a clearance of 250 feet – the absolute minimum I would contemplate as a GM, 500 would be better – puts a character over the limit.

This section of rules is all about effort required, and recovery of damage, and has very limited utility with other game systems. GMs may want to calculate the Pressure number anyway, simply for the utility of rule 2, relating to the ease of starting fires and the effect of fire damage. D&D HP can be considered roughly equivalent to Hero-system Stun points, so the “-3 damage per pressure number” from fire would be appropriate.

The recovery rate can also be applied by a D&D GM for protracted stays at altitude, and the effect on regenerating creatures.

Game Effects: Rain/Snow

This is quite straightforward. The GM decides on a description for the conditions and reads off the appropriate modifiers.

3.x/Pathfinder use: The Perception modifier should be applied to Spot and Listen checks. The Range Multiplier should be used to determine the attack modifier for ranged attacks, and the OCV modifier applied on top of that to all attack rolls. The DEX-based skill penalty should be applied to all skills that are based on DEX.

Game Effects: Extreme Cold & Heat

Now we’re getting to the crux of the system. Indexing the difference between a range that the character finds comfortable, allowing for the clothing he is wearing, and any acclimatization that may have taken place, to determine game effects.

Let’s say we’re talking about a character who is used to cold temperatures; acclimatization gives them a comfort zone of 6°C to 23°C. Yes, I know these values aren’t on the temperature conversion table; if you are used to °F, use 35°F to 65°F as a rough guide.

There are two ways to handle the effect of appropriate clothing; the method described in these rules (adjusting the comfort zone) or the one we came up with in play, reducing the effective number of temperature levels, which is less accurate but much faster and easier.

In our example, we have an effective temperature of -45°C (-43°F).

Rules as written, °C:
Comfort Zone for an acclimated character in several layers of heavy clothing: perhaps -10°C to 7°C. The gap from -10°C to effective temperature (-45°C) is 35°. That gives a thermal level of between -11 (=35/3) and -7 (=35/5). A level of -9 is right in the middle, but the higher range value is more appropriate for a cold-acclimated character, so use a temperature level of -7.

Once you have this number, there are two tables in the rules – one is for hot temperatures, the other for cold. A temperature level of -7 indicates an effective loss of 7 Recovery, -6 to DEX checks, -5 to attack rolls, -6 to all DEX based skills (on top of any other penalties from snow or rain), and 2 END consumed every 5 minutes on top of any other expenditures, just from moving around, breathing, etc.

Rules as written, °F:
Comfort Zone for an acclimated character in several layers of heavy clothing: perhaps 15°F to 45°F. The gap from 15°F to effective temperature (-43°F) is 58°. That gives a thermal level of approximately -6 (58/10) to -3 (58/20). This is quite a bit lower than we got for the °C calculation because the size of the intervals (10-20°F) is wrong. It should be 9/5ths of the °C value (5.4 to 10.8) – call it 5 to 10°F – but… well, there’s no other way to put it: I made a mistake.

Using the CORRECT values gives a range of -11 (=58/5) to -6 (=58/10), almost exactly the same as the °C calculation. Again, an acclimated character should use the smaller of these numbers, the -6.

Quick and Dirty, °C:
Comfort Zone is defined as 10°C to 27°C. Acclimation lets the character reduce the temperature effect by 1 level, appropriate clothing lets the character reduce it by another 4. Difference from effective temperature (-45°C) is -55°. Temperature effects range from -11 (=55/5) to -18 (=-55/3), which is then reduced by acclimatization and clothing to -6 to -13. The -6 is more appropriate for an acclimated character.

This variant takes a vaguely-defined step out of the process, but gives a somewhat broader range of values and skews numbers toward the high end for those not in appropriate clothing. But it’s close enough.

If you want to compensate for the skew, use an interval range of 4-5 instead of 3-5°C to calculate the step size: 55/4=14, which reduces to 13 with acclimatization, and to 12 with light clothing, which is about right.

Quick and Dirty, °F:
Comfort Zone is defined as 50°F to 80°F. Acclimation lets the character reduce the temperature effect by 1 level, appropriate clothing lets the character reduce it by another 4, exactly the same as the °C version. The effective temperature is -43°F, a gap of 98°. Using the correct values gives a thermal effect of -20 (=98/5) to -10 (=98/10), but that becomes -15 to -5. Again, a broader range, and the numbers for those in inappropriate clothing are skewing higher than they should – but you can allow for that by changing the interval size to 7-10°F. But division by 7 is so messy that I would be tempted to double the range and use 15 (effectively a 7.5° value).

On reviewing the article, I realized that this might not be obvious to anyone not used to such arithmetic tricks.

Double 98 is 196. Divide that by three and you get 65 and one third, which can be ignored. One fifth of that is 13, which is exactly what you would have gotten by dividing the original 98 by 7.5.

You could make it even easier: double it twice, and divide by 30: 98->196->392; divide by 3 to get 130 and 2/3, which can be ignored because a second from now it will be 2/30ths, a trivial amount; divide by 10 to get 13.

Oh and for one final trick: it was a lot easier to double 100-2 twice to get 400-8 than it was to do the calculation the hard way.

Game Effects: Wind Velocity

The final section of the rules, it’s fairly self-explanatory – and for a change, I gave wind velocities in both km/h and mph, so that makes it fairly easy to use. And if anyone needs values for anything bigger than an F8, I don’t really want to be there when it happens!

The Impact of Genre

You can’t repeatably give the appearance of danger without posing an actual danger to the PCs. Pulp adventurers are supposed to overcome danger and death in the course of their exploits. These rules were designed to increase the danger level experienced by the PCs while providing sufficient latitude that smart play could minimize those risks.

While this is a focal point of the pulp genre, to a lesser extent it applies to almost all RPG genres. It follows that these rules are also relevant to almost every genre, at least in principle; only the degree of latitude shown in terms of the protection from the elements offered by clothing changes.

One concluding note

If I had access to the original document, I would have edited it before presenting it here, having discovered the conversion errors discussed above. Unfortunately, the editable version is still on my main computer, which I still haven’t had time to get running since it’s total failure last December. It’s only been, what, eight months now? (A Brief Heads-up: Why I may miss posting)

When opportunity permits, I’ll correct the original, upload a revised PDF, and redact this article accordingly. Until then, you’ll have to make manual corrections, I’m afraid. Or simply use the °C methods that were originally designed and tested.

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