The Firmament is an unbroken layer of clouds that wreathes the entire planet. The inhabitants of this world have never seen a blue sky, nor a star-spangled night. The intensity and quality of ambient light does shift in predictable patterns, but there is no sunrise or sunset, no discernible horizon.
Rain, thunder, and lightning are common meteorological phenomena, as are tornado-like vortexes that sometimes join the Firmament above with the Shroud below. Most of these weather patterns have approximate “seasons”, making them somewhat predictable, but there are outliers.
Other, more curious phenomena exist, although many of them occur far from any stead, and therefore are only noted if someone happens to be traveling nearby. Legends of all sorts of strange things and happenstances exist, from flocks of unknown flying creatures, impossible lights in the sky, even shafts of brilliant energy lancing down from the Firmament.