The issue of day/night cycle and weather has been raised many times in the forums but apparently Larian said it’s impossible due to co-op play. I have no idea why that’s the case but regardless it seems we will have to traverse the Sword Coast in permanent sunlight which is utterly immersion breaking for me personally. The people working on the game interviewed in the Panel From Hell live stream talked about creating a living world...sort of laughable that the world we traverse has no weather and no night time.
For anyone who ever played Warriors of the Eternal Sun on the Sega Megadrive/Genesis you’ll be familiar with playing a DnD game where the sun never sets.