Fair-Weather Friends

Albert Bierstadt - Approaching Thunderstorm on the Hudson River

Oh boy.  There are certain aspects of running D&D game worlds that define the meaning of “polarization”.  There are groups that embrace rules of encumbrance, mass combat, specialty critical hit and miss charts, flanking rules, and so-on and so-on. For me it’s weather.

Weather is a complicated little piece of D&D minutiae. The Tao of D&D blog stated the problem of weather best in the post: The Weather Problem Described.  I am using that as the impetus for understanding and compromising my own approach to weather in my world.

For me, successful weather needs to include variable temperatures, precipitation, and wind (obviously).  It should also include a chance for severe weather on any given day.

I have tried, like so many DMs before me, to create some simple way of generating pseudorandom weather.  At its most basic, a simple table that has some aggregated description of weather that a DM rolls against can be sufficient, albeit probably not so relevant or realistic.  “Roll a d20. Okay, a 7.  Today’s weather is Windy, Partly Cloudy, and Warm.” Sure that’s fine for what it is.  But that simplicity lacks for me.

On the other side, I have seen complicated charts and compiled tables that take into account for various climates, seasonal changes, wind chill factors, armor effects, exhaustion, and outside forces that influence weather.  I am looking at you AD&D Wilderness Survival Guide. They can result in quite a few lookups and rolls to determine the weather.  I’ve seen a few where they re-roll weather every hour.  So in summary: that’s too much for me.

Finally, weather should influence not only the PCs, but the NPCs and the area surrounding them at a given encounter (combat or story). There are DMs who just don’t subscribe to even the minutest amount of “bookkeeping” and will hand-wave weather as just non-story related obstacles.  I personally do not feel that way, as it provides real-world feel and every player understands weather and how it could affect them.  Yes, there is a possibility it is an obstacle or conflict, but that is the point!  Weather can force your players out of complacency when fighting.  It can even out slightly lopsided fights as well.  It gives the DM more scene descriptors.  It gives Players more roleplaying prompts. Think of weather as another omnipresent NPC.

A word of warning though.  Many DMs do not like to use Weather because it needs to always be there, always ready to respond to the characters when it is pertinent. It needs to be present from day-one of the campaign, be seen each and every day.  It needs to be a consistent thing for players to know might be an obstacle for them to overcome.  Don’t let your characters purchase all manner of gear to handle weather situations, and not meet them halfway by not managing the weather.

Design Requirements

To find a balance between enough detail that gives interesting elements for the players to grab onto and use, as well as, keep the details relatively easy to generate, is the main conceit. Weather should have a few assumptions, and within a few rolls, create meaningful temperatures, winds, and precipitation.  There also needs to be a chance for severe weather that can override everything for variety and realism, as well as, potentially new story directions.

I want slight temperature fluctuations from day-to-day, with the possibility of hot/cold snaps, but fairly steady during a given day. I also do not want to determine intra-day temperatures. Lastly, I want precipitation and wind gusts to fluctuate from encounter to encounter during a day.  For example, today the temperature high/low will be 79F/58F, 60% chance of rain showers, wind gusts up to 24 MPH. Then both precipitation & wind get specifically determined when an Encounter is triggered.

I also want all the information to fit on a single piece of paper as a Weather Worksheet. Then I will build a 2-page Session “Almanac” tracker that will include the Weather Worksheet as the back page.  The Almanac Tracker will be for another post.

I should note the way I generate weather is to determine the Temperature at the start of a day, then a worst-possible Precipitation possibility, then the worst-possible Wind gust possibility, that may occur when it is relevant.  I also make a simple 1% check for Severe Weather on a given day.

This is the 2nd page of a document I call my “D&D Daily Almanac“, which I will review in my next posting. Here is page 2, the Weather Worksheet:

 D&D Daily Almanac - Page 2Note: I do try to include both metric & Celsius measures, but they are not exact reciprocals of the US standard units of measure, only approximations.


1. Determine Normal Temperatures

For me, it all starts with Normal Temperatures.  I make the assumption that DMs know the average temperature for a given time of year and/or climate of the location where the story is taking place on any given session.  It is the DM’s world afterall.  I also make the assumption the weather is probably similar to our lovely planet Earth, for simplicity.  Normal Temperatures are an amalgam of climate and seasonal changes (like AC is an amalgam of armor, dodging, and other hokum), and all are broken into Monthly Averages.

Weather Worksheet - Normal Temps

With that in mind, I know the region of the world and I know the climate of my story.  For example, I have a version of the Neverwinter, from the Sword Coast in Forgotten Realms, in my world. It resembles, climate-wise, like the North American Pacific Northwest, and Vancouver, B.C. Canada in particular.  Waterdeep = Seattle, WA; Baldur’s Gate = Portland, OR etc.

I used average temps from Vancouver, BC for my Neverwinter, but bumped it up to reflect the warmer influence of the Neverwinter River (story canon).  Once written it would look like the following (the current month is June):

Weather Worksheet - Normal Temps Example

Normal Temperatures then become the “seed” to generate daily weather.  One of the big requirements is that temperatures should have “memory”.  It should know yesterday was below average for the day, and a trend is starting.  You should have a way to allow for a streak of below unusual temperatures (cold or warm trend), but then have the ability to rebound back toward normal (reset).  Those effects will be determined by the daily temperature changes.

2. Determine Temperature Changes

The next step is to determine how the Temperature Change for the day.  After looking at different approaches, I wanted a bell-curve of data, where the bulk of data is normal or near-normal (change by a degree or two per day).  Then the as the chances get smaller, the temperature can get more extreme.  I also want to be able to roll a simple 1d100% to determine the day’s temp change.

My temperature distribution looks like this:

1% Warmer (+7°F / 4°C)
3% Warmer (+5°F / 3°C)
6% Warmer (+3°F / 2°C)
15% Warmer (+2°F / 1°C)
15% Warmer (+1°F / 1/2 °C)
20% Normal (Reset to Normal Temp)
15% Colder (-1°F / 1/2°C)
15% Colder (-2°F / 1°C)
6% Colder (-3°F / 2°C)
3% Colder (-5°F / 3°C)
1% Colder (-7°F / 4°C)

With this distribution, I should have 80% chance to have weather within +2°F/-2°F, or +1°C/-1°C.  Also, I should note that to prevent excessive swings in temperature trends, the middle portion (20% Normal) will reset the temperature for the day to Normal.  Over an average 30-day month, this distribution runs close to average but still allows for possible streaks of cold or warm for the month. When a new month begins, the Normal Temperature is set.

Regarding the rates of increase, I wanted to roll dice.  And to that end, I wanted to use only commonly used dice (d4,d6,d8,d12,d20).  So a 1d4 was the intended to be used, and as you got warmer or colder, more dice would be rolled.  Unfortunately, the temperature swings were too extreme to work. A possible +4°F/-4°F series of change is just too much, especially during the extremes of a year (heat of summer, cold of winter).  I had a few data runs that with a 85°F Normal Temperature, could grow into a 135°F within a 30-day period. This actually helps me understand why Climate Scientists claim that just a single degree change has dramatic impact, when you aggregate that data.

To Determine Temperature change, roll a 1d100, then find on the “meter” the degrees change for the day.

Below for example, if you roll an 18, your temperature is +2°F/+1°C from yesterday’s temperature.  If you are tracking both highs and lows, roll for each.  You could possibly have a situation where the Low could be warmer than the High, or the High lower than the Low.  In either case, if that occurs, set the Highs & Lows equal for the day.

Weather Worksheet - Determine Temperature Example

3. Determine Precipitation

Now that the temp for the day is known, we need to determine precipitation.  I wanted to have a decent range from seasonal rainstorms all the way to snowstorms.  Either end would be considered extreme within this range, but not as extreme as severe thunderstorm or a heavy blizzard.  Those possibilities need to be accounted for, but would be determined separately.

I also do not want to account for accumulated precipitation here, but allow for possible after-effects when Severe Weather occurs. Lastly, I want the type of precipitation be affected by the temperature.  If the temp is above or below freezing, then a more appropriate precipitation is described.

To Determine Precipitation, roll a 1d20, then find the precipitation, whether it is above or below freezing.  Then roll a 1d10% chance for that extreme precipitation for the day. When an encounter takes place (combat or otherwise), have a contested roll 1d10% roll.  If the % encounter roll is less than % chance, then that precipitation type occurs.  If Rain, Rainstorms, Snow, or Snow Storm occurs, mechanical obstacles occur as well.

For example, I rolled a 1d20 and got a 17.  Today there is a chance of Rain.  Then I rolled a 1d10%, and determined a 40% chance of rain at any given time.  My characters are fighting in a grassy field against a small horde of Goblins.  I call for initiative, then roll my 1d10% and get a 20%.  In this case, the occasional small shower has little to no effect on the encounter.

Example Worksheet 3 - Determine Precipitation

I should note that if the 1d10% had exceeded the 40%, then no Showers would occur, and I typically shift one square toward Clear Skies.  For example, if I had rolled 90%, then no Showers, and I would describe it as having Overcast skies, and is not impactful at the moment for the encounter.

4. Determine Wind

Wind is pretty interesting.  Wind fluctuates the most within its range on a given day, meaning it goes up, down, up again, down again.  It sustains for a while, then runs calm. Even the most windy days, have moments of calm.

To reflect for wind, I want to set an extreme for the day much like I did for Precipitation. (step-approach).  In this case, each step represents a number of dice to be rolled when determining Wind at any given encounter.  I use the general Wind Classification of 10-minute sustained measures to define wind levels (0-5).  Meaning, when you roll for wind during any given day, it is assumed that wind is sustained for a minimum of 10-minutes.  I also assume that the wind speed covers an entire encounter, as for the majority of encounters may never exceed 10-minutes.

To Determine Wind, roll a 1d20, then find your Wind Factor.  It does not matter which side of “0” you choose.  So for example, if you roll a 12, your Wind Factor is 2. Then when an encounter occurs, roll a number of dice equal to the Wind Factor (MPH = d20s; KPH = d12s).  Then you can determine Wind Direction optionally.  I use a special d8 Direction Die, but you can use anything. I rolled 2d20s for 16MPH wind, blowing North for the encounter.

For my world, if the speed > 25MPH/40KPH, then Ranged Weapon Attacks and Perception (Hearing) checks are at Disadvantage, and open flames are extinguished.

Example Worksheet 4 - Determine Wind

5. Determine Severe Weather Chance

Finally, I check for severe weather.  This weather potentially overrides any and all the data from above.  A DM needs to choose an appropriate type of severe weather for the climate and time of year the characters in.  The Weather not only has potentially devastating immediate effects, it also may have harmful after-effects.  The weather can also be story-changing, much like real world weather can.

To Determine Severe Weather, simply roll 1d100, and if it is 100, then manually choose an appropriate weather for a given day.  Follow the information for selected weather, and adjust as needed.

Weather Worksheet - Determine Severe Weather

Final note.  Of course this is abstracted weather.  This is a mix of oversimplification and abstraction, but a higher degree of detail than most others.  It has been working in my world.

Here is a link to the 2-page PDF: D&D Daily Almanac

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