There are definitely some differences in how people are defining terms on this thread.
BBC Bitesize* - not a definitive source on advanced literary criticism, obviously, but probably a good guide to how exam boards expect the terms to be used in secondary schools - says this:
Be careful: don't mix up pathetic fallacy with personification.
- Pathetic fallacy is always about giving emotions to something something non-human.
- Personification is giving any human attribute to an object. For example, 'The wind whispered through the trees.' or 'The flowers danced in the breeze.'
Of your two examples, I'd say "the storm raged" meets these definitions of both pathetic fallacy and personification: it's ascribing the human emotion of anger to something non-human.
In some instances of pathetic fallacy, the weather is definitively ascribed emotions: "clouds wept fat tears over the grey town" or, more mundanely, "it was a miserable day". Here the pathetic fallacy is inherent. Your second example of "the grey clouds filled the sky" seems a bit more nuanced. The words in themselves seem to be neither personification nor pathetic fallacy. They're just a factual statement about the weather.
I suppose the key thing in your example is that the grey clouds occur when the character is unhappy. When the writer and/or reader notice this correspondence between the "miserable" weather and the emotional tone in the story, this is the pathetic fallacy. But you can't always definitively identify pathetic fallacy from the words alone: maybe the weather is a necessary part of the plot, because rainy conditions will lead to a character being washed away in a flood. Or maybe it's just how it is: the weather is a bit dreich because the story's set in the west of Scotland.
Presumably this sort of pathetic fallacy, like symbolism identified in literature more generally, is often not put there intentionally by the writer but arises in the mind of readers. It isn't a writing technique as such, but something that may arise naturally and resonate with readers. In a survey circulated to 150 writers in 1963 asking about the use of symbolism in literature.** I've enjoyed reading the example responses I've come across:
- Norman Mailer: "the best symbols in a novel are those you become aware of only after you finish the work".
- Saul Bellow: "Symbol-hunting is absurd, but it is encouraged by teachers of lit."
- Ray Bradbury: "Each story is a Rorschach Test ... and if people find beasties and bed-bugs in my ink-splotches, I cannot prevent it ... Still, I wish people, quasi-intellectuals, did not try so hard to find the man under the old maid's bed. More often than not, as we know, he simply isn't there."*