The Queenbite

Every year, in the depths of winter, a horizon-spanning storm, known as the Queenbite, appears on the Bluecap Sea, heading towards Whitelake and The Nonary Land. Common theory is that the storm is spun up by Umberlee in a fit of pique and temper, an expression of her rage towards the Divine Aegis and all those under its protection.
The Queenbite is a cyclonic blizzard, strong enough to cause waves to drown and crush ships, persistent enough to wash over a massive swathe of The Nonary Land, freezing everything before it.
The Church of the Nine Gods does what they can to shelter the peoples of Whitelake; offering storm basements, magical wardings, enspelled stones for warmth, and free food - but nonetheless, every year, some people freeze and die under the storm's wrath.