A warm front.
With persistent hard rain.
Inspired by an Australian TV graphic of a weather front building up on the coast near Sydney. This took the form of something that might have been viewed, by the impure of mind, as a toilet-wall doodle of the classic meat and two veg. The completely knowing text was also packed with innuendo and double-meaning.
In other fics I have introduced Ankh-Morpork's need for a reliable advance weather-forecasting system. The University – and HEX – have taken on this public service.
Sometimes it generates scenes like this.
"Sti-BBONS!"
"Yes, sir?"
Ridcully brandished the weather forecast, as generated by HEX, under his nose. Ponder Stibbons took it, glanced at it, then blinked and did a doubletake.
"Have a word with those damn people in Meteorology and Weather-Scrying, would you?" the Arch-Chancellor demanded.
Ponder frowned. Asking the young students in Meteorology if they could, you know, do a sort of graphic picture of the weather-fronts, so that it could go direct to the Times for publication in the morning edition, you know, a visual representation. Well, it had seemed like a good idea at the time. Good PR.
"And the Times... you know... printed this?" he said, slowly. The morning edition ran to quite a few tens of thousands of copies. And the air-mail people flew out with the overseas editions... another horrible thought gripped him.
"This goes to City institutions first. People with an interest in knowing what the weather might do. The Navy. The Clacks. The Rail Ways. The Post Office... the Post Office...
"Ridcully nodded, emphatically.
"And the Air Watch, laddie. Fortunately those young Witches are broad-minded and thought it was a huge laugh."
Ridcully frowned again.
"Young Olga Romanoff says they've pinned it up on their bulletin board and they're askin' if we can expect any more weather like this. And she said she thought it wasn't that big a laugh in the first place."
Ponder winced.
"But, sir.. the Post Office..."
Ridcully smiled, the smile of a man who has it all worked out.
"Miss Maccalariat's on her way over, lad. You're dealin' with it. You're Chair of Public Relations, after all."