You can control the global chance of rain/snow-compatible maps to precipitate.

To do so, you need to change the RainPctChance value in the XComGamedata.ini file.
Accepted values are between 0.0 (0%) and 1.0 (100%). The default value is 0.3

This mod has an attached copy of XComGamedata.ini file with the following settings:


In this example, the vanilla (0.3) setting is removed and further replaced with a custom chance of 0.5. You can change that 0.5 value to something else, e.g. 0.2 (very low chance) or 0.9 (very high chance).

ANOTHER WAY TO DO THIS:
If you think this is not working for whatever reason, you can make a manual tweak in the original instance of the XComGamedata.ini file. It is located in the following directory:


Inside the file, find the RainPctChance value. It should be right under the [XComGame.XGStrategy] config header. Change the value to a desired one and save the file.

Make sure other configs from other mods (i.e. other XComGamedata.ini instances) are not overriding the settings. For example: I know that Darker Nights mod has one, so you might need to delete its config copy/lines if you're using that mod.

Remember: whatever you do, the [XComGame.XGStrategy] header needs to be above the RainPctChance setting.


If the weather RNG is not in your favor, you can manually activate rain/snow during a mission.

First, make sure you have the console enabled (instructions)

Open the console and type the command:
Additionally, you can separately toggle the wet surfaces (puddles, wet roads, etc.). This is relevant mostly in city missions.


This enables and disables the wet surface looks, respectively.