Its the little things that make a game world come alive. A bit of detail here and there that is not even plot relevant but perhaps just something that is added to the narration. A change of weather now and then can make the game world feel alive …and if its the freakish, unsteady weather in the dry badlands of the post-apocalypse a sudden change might become a small adventure in its own right as the characters have to deal with the new situation.
The following table is a simple example on how to add weather and weather changes at random to a scene. Just roll 2d6 to determine the weather and perhaps another 2d6+2 to determine how long it lasts in hours. Unless it is a weather phenomenon like heavy rain, a dry thunderstorm, a tornado or a sandstorm, in which case one better rolls a d6 and subtract one to determine the duration in hours. If the result is null or negative, the weather phenomenon stays for far less than an hour. Oh! And you might want to rule that a certain weather condition will not repeat itself for the next few days / weeks / month and thereby re-roll certain result, especially if it is “Heavy Rain”.
Heavy Rain is a real downpour of precious water, so there might be a chance that it is acidic, black from ashes or radioactive, depending on the game world. During “Heavy Rain” flash floods can happen while streets, roads and paths turn into deep stretches of mud next to impossible to traverse.
A Dry Thunderstorm brings clouds, thunder and lighting strikes but no rain will ever touch the surface. Skill tests for Survival might be in order to find shelter, ot there might be a (slim) chance of actually being hit by a lighting strike, especially if one is out in an otherwise open field. Dry Thunderstorms often cause fires in the surroundings (if there is any vegetation left that could be set a flame).
Heavy wind, carrying sand limits sight drastically and is very unpleasant, to say the least. Without eye protection it is next to impossible to keep the eyes open and the head up.
A Light Breeze is a common and desirable weather condition in the dry badlands while Windless Heat is a scourge to those traveling it. With the air standing still, the heat gets even more punishing.
A Light Cloud Cover is a blessing to those out in the wilds, as any obstruction of the sun is welcome, no matter how thin.
When a Sandstorm is coming, one can only seek shelter.