How are Mass Outbreaks determined?

Question

You all know about the Mass Outbreaks of Pokemon, where a special Pokemon appears on a certain route, and each day, it changes. Does anyone know how the game determines the next Mass Outbreak?
Note: I'm talking about 4th & 5th Gens. Thanks!

HB

Comments

What game or generation??

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I think it randomly selects it.

Answer 1

Its just random

Source-Experience