Thank you all for y'all's input. I'm still turning all these takes over in my mind.

This came to me in an odd way, I guess: we had three snowstorms in the previous two weeks, and I thought, "the snow is relentless." Then I thought, "the snow is unrelenting." I stuck with the latter even though (or maybe, because) it seems I'm anthropormorphizing the snow -- like it's doing what it's doing just to give *me a hard time!

Can a natural event be unrelenting?