Answer:
Foreshadowing
Step-by-step explanation:
Foreshadowing is the technique that allows the author to forward some information about something that will happen in the narrative later on. In the sentence "The Western Daily Mail could run that forecast every day - for all I know, it may - and scarcely ever be wrong.", We can see that the speaker confirms that what was predicted in the Western Daily Mail will happen at some point of the story being told, that is, the author advanced an event, leaving the reader curious about how the narrative will flow and how that event will influence what is being narrated.