This is my first attempt at a Dying Light mod and I 'think' it works as intended.  The purpose of the mod is to make it storm all the time. 

Unzip the weatherdata.scr file into Documents > Dying Light > out > data > scripts directory
Start up your game.  After the player sleeps it should storm all the time after that.

Endorse if you like and let me know if there are any glitches.  It shouldn't interfere with storyline specific weather due to how those events are scripted.