An accidental Fimbulwinter?

It's cold, and the days grow darker, but we are well.

But still, I can't help but wonder: What if one of these years it actually didn't start getting brighter with the solistice, all because some pesky shamanistic priest somewhere forgot which day it was, or was at the hospital, and by the time he realized what had happened, things had gone too far for a simple ritual to fix.