As the title states, rain and snow can appear and disappear if the player changes height, generally on the edges of biomes. For instance, in seed 6098993085410235807, if you do /tp 3526.69 149.72 2007.78 334.79 90.00, then fly up and down while it is raining, you can clearly see snow and rain planes appear and disappear. I strongly suspect that this is due to the precipitation rendering code using the player's y-coordinate in place of the motion_blocking heightmap, though upon consulting the game's code using mojang mappings i do not see a clear location where this might be happening, though the code isn't the clearest. here is a video very clearly demonstrating the problem with the above setup: https://youtu.be/WqJTfYPVKyk