Unearthly pillars of light from high altitude crystals reaching ground level
Every single one of these mythologies started out as an oral record of something that really happened and it gradually became an embellished narrative.
Did the Vikings know about the signs in the heavens that preceded the arrival of another Ice Age?
If they did, they would have recorded them in fables and tales that kept the essence of the story, so that their children would not be taken unawares the next time.
The Winter of Winters approaches. We're not prophets at Vault-Co. We simply have eyes.
It is no accident that the arrival of the final cold always leads to apocalyptic war in the Viking sagas.