Tension

[Ultimatecalibur]

No, the change took place months before 2.5, sometime around september 2014. Before the fall wasn't until january 2015.

You mean roughly when the Odin Trial was added to the game files for the 2014 Fanfests?

[Gemina]

Even after the calamity, with places like Tam-Tara-Deepcroft, Haukke Manor, Amdapor Keep, and the Lost City of Amdapor; an elder primal wandering around and slicing the unworthy in half, and the weather constantly gloomy, the Black Shroud earns its name.

The tension weather is very fitting for Odin, and just makes him out to be all the more badass that he has his own weather that lets everyone know he's around somewhere. It's very reminiscent of John Carpenter's 'The Fog'.

[ChiiSoSeriouz]

I think it was more of a localisation change then a lore change seeing as they updated other weather names at that time like clear/fair skies and leviathan's torrential to rough seas. But it sure is a good theory.