Steps to reproduce
Create a world in a cold biome, for example, using "jagged peaks" or "snowy village" from the seed picker.
Change weather to rain.
Fly upward to Y 375.
Expected result
It's snow all the way up.
Observed result
Rain occurs from Y 315 to Y 369. It blends with the snow for a few blocks at each end and is rain alone from about Y 321.5 through Y 354.5.
This is not just a case of MCPE-9541. That ticket seems to be about weather mixing across the horizontal temperature gradient between different biomes. This report is about what seems to be an unnatural vertical temperature gradient above cold biomes. It may be related to the newer vertical biome mechanics, with cold biomes cutting off at build height and a warmer default biome being used above build height everywhere in the world. The transition to snow at Y 370 matches the plains biome (tested in a flat world).