How is it that Dementors are able to affect the weather when they're breeding? In Half-Blood Prince, Fudge tells the Muggle Prime Minister the strange weather the UK is experiencing is due to the Dementors breeding:

Even the weather was dismal; all this chilly mist in the middle of July ... it wasn’t right, it wasn’t normal ...

Half-Blood Prince - page 8 - British Hardcover


‘But,’ said the Prime Minister, with a sense of dawning horror, ‘didn’t you tell me they’re the creatures that drain hope and happiness out of people?’

‘That’s right. And they’re breeding. That’s what’s causing all this mist.’

Half-Blood Prince - page 20 - British Hardcover

As well, there's this:

J.K. Rowling: Yes, the world seems a much sunnier place (literally – with the Dementors gone the weather gets better!)

J.K. Rowling Web Chat - The Leaky Cauldron - 07.30.07

I understand how Dementors multiply, but I can't quite figure out how the Dementors' breeding would manage to affect the weather. How does it?


1 Answer 1


I'd say it's a matter of quantity. When some species are in their breeding season, they all migrate to a specific location and start the frenzy of looking for a mate. My guess is that, in a similar fashion, dementors are constantly in the move, so they leave that cold feeling for a short while, until the next one comes, which shouldn't take too long because another one is bound to appear sooner rather than later.

What we could argue about is the reach. If a single dementor can disturb the weather in a radius of a mile and leave it cold for one hour, and assuming they can move 2 miles every hour, it would take 30 dementors to constantly cover the area of London (~600 sq miles).

Considering Harry, Sirius and Hermione were attacked by some 100 dementors, and that many others would have stayed to guard the prison, it seems reasonable to say that there were a few hundreds dementors before they started breeding, which would allow them to affect the weather in a few thousand square miles at the same time, an area which might have grown as they increased their number.

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    While I really like the answer, I cannot help but feel the math is a bit off. It would indeed take at least 30 dementors to cover the area of London, but that would assume they'd be at roughly a double radius away from each other, and stationary. In breeding season, I can hardly imagine this to be the case.
    – Joost
    Oct 29, 2014 at 16:37

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