Wintersmith begins with another storm (once the book gets going after the glossary). This is a common PTerry openning. I wonder if he did it first to prove that a good book could begin with" a dark and stormy night" and kept doing it because he was right. Why return to it now? Probably because of the title character but maybe to tie it to other discworld novels, or to comfort and reward fans reading thier first YA novel or maybe because it's worked before. I begin each novel admiring his prose then noticing it less as I get pulled into the story so I read them twice to start. Opinions on PTerry opennings and storms anyone?

Hm, I have to check out that one... when I finished the paper I'm sitting on. I thought a lot of the novels were starting by a zoom on the turtle... You might be right though.

Well, it is winter and Tiffany is having a face-off with the Wintersmith...

The only other book I know from the top of my head is Equal Rights.
Then again, my head is spinning right now.
One point in case discaimer's observation is right, though: A lot of things on Discworld are caused by narrative law (tm)... And if narrative law says a certain kind of story has to start in a dark and stormy night, well...

and Stormy night-that opens "Wintersmith". The Book begins with a Winter snowstorm and it starts out with the Feegles observing the full snow clouds which to me indicats that the storm is taking place in the light of day. So it was a gray and stormy day--plus a bit later in the same beginning narrative the comment is made that "the light from the windows was coming through snow". However things on the discworld do seem to happen when the weather is rather inclement. (Dwarfs Turning Iron into Glod, etc.)
I don't feel that despite the Narrative Law of the disc that Pratchett necessarily lets that dictate how his books open.

There's also a dark and stormy night in GG.

And don't forget Wyrd Sisters. That's the one with the drama queen storm, right?

Aren't all nights dark?

Some more than others...