On one of the maps in City Ruins, I spent a few days there. The first 2 or 3 days, the sky box was normal, snow, rain and blue sky, day and night. But I think on the 3rd sunset, I noticed fire started to appear in the sky around the map.

I freaked out and hit end exploration lol.

Anybody stayed around long enough to find out what it was? Was it some sort of shrinking death bubble thing?