Not sure if this is a bug or a feature not yet in MCPE.

The temperature of a region of a biome should drop by 0.00166667 per meter above sea level (Y=64) and rain should change to snow when the temperature of the biome or part of a biome is lower than 0.15. See http://minecraft.gamepedia.com/Biome

I tried elevating some parts of a few different biomes that are closest to the 0.15 threshold to make it snow "up there" but all I got was rain

For example, in extreme hills I built a solid 6x6 column up to Y=125 (build limit - 2) so the 0.20 base temp at Y=64 should become 0.10 and give snow. Nope.

Screenshot_2015-09-24-22-49-11.png shows another column/extended platform at Y=125 in extreme hills getting rain instead of snow.