[Jürgen Hubert]

I remember such tables in certain gaming D&D books, but I can't look it up right now.

However, here's a quick and dirty way of doing it in GURPS: Make a random roll on the Reaction Table and substitute "weather" for "NPC":

1 to 3: Very Bad. The weather dislikes the characters and will act against them if it’s convenient to do so...