Over at ComicBookResources.com, there’s a series called “Comic Legends Revealed”. The second legend revealed in their 273rd post is:`
COMIC LEGEND: Len Wein came up with an amusing tribute to Snoopy’s Great American Novel in a Batman short story he did with Walt Simonson.
“It was a dark and stormy night” first appeared at the beginning of novelist Edward Bulwer-Lytton’s 1830 novel, Paul Clifford. It has become one of the most famous example of “purple prose” ever.
In July of 1965, Charlie Brown’s dog, Snoopy, first began working on his novel, and sure enough, the phrase opened his work.