Weather in your RPG
Introduction
When it comes to weather many Games masters handwave it, or only make use of it occasionally. It's another one of those things to keep track of. The other problem is how do you go about deciding on the weather for the day.
In this article I'm going to look at various ways of dealing with weather in your game and maybe one of them will suit your style of running games. It will begin with some simple solutions.
Simple Roll
The easiest way to deal with weather is at the beginning of each day roll a dice, the type of dice you roll can be dependant on how often you want it to change. The higher the dice type the less chance of a change of weather, so a d12 will give less changeable weather than a d4. When you roll the dice if a "1" is rolled then there is a change in weather. It is up to the GM to decide what the new weather is and how it aides or hinders the players.
Historical Weather
Another easy solution is let historical data do all the heavy lifting for you. Find the historical weather for a real world location with a similar climate and use that on a day by day basis. Mirror the days in your campaign with the real days in historical data.
The best I have found is wunderground
Online Random Weather Generator
There are several online weather generators that will do all the heavy lifting for you. Select the climate and season and it will produce the weather for you. The most effective one I have used is by Donjon Donjon
Self-Created Online Weather Generator
You can create own weather tables at Perchance and access them for free. The syntax is quite easy once you get used to it. Roll on a main table which then leads to smaller tables. You can have different tables for different seasons and/or climate. The first table leans heavily to normal weather with a much smaller chance of extreme weather. When a line is selected it choose the look, temperature, rain if there is any and wind from other tables. You can add to individual tables as you see fit and give each result in a table a different weighting to be drawn.
The downside to this is the weather can change quite a bit from day to day if you don't carefully craft your tables.
My random weather table from Weather in Middle Earth show this to good effect (click on the edit button to see the data behind it). Feel free to copy and create your own table from this.
Dragon Magazine
Back in 1988 in issue #137 of Dragon Magazine, Lisa Cabala wrote a very detailed guide on how to make realistic weather for your game. The idea is to look at climate and latitude and roll on a number of tables (19 in total). The idea is you would pre-roll the weather for your campaign for days, weeks or years in advance and cross each one off in order as you use them.
The Magazine can be found at the Internet archive Dragon 137
If you find this too daunting, Alexander Barrett has converted the whole article to a Google sheet which will automate the process for you Google sheet
Hex Flowers
Goblin Henchman came up with the Hexflower system for random tables with a memory. One of the tables he created was made for the current weather. It uses a 2d6 system (which gives more weighted results to be middle numbers) The weather is generated by performing a “random walk” across a 19-hex grid, each hex corresponding to a weather type.
There are some simple rules in the direction you travel and what happens if you exit the hexflower. The only slight downside to it is you need some method to record the current weather by using a token on a printed version of the Hexflower, or have a separate VTT screen to record the weather progress.
Simple Markov Chain
The final one I recently came across is the Simple Markov Chain which addresses the randomness of weather. weather is one of two state Settled or Unsettled. The basic idea is to roll once per day to determine if the weather remains Settled or Unsettled, or if it flips to the other weather regime. If the weather is Settled it remains the same until an Unsettled result occurs. when unsettled the weather changes every day. Again different tables are required for the seasons
The article behind the system is Simple Markov Chain
A complete PDF can be downloaded here
Conclusion
So there are some ideas for you, I have used them all at one time or another. If you want weather in your game, there really is no excuse now.