My flat testworld has Extreme Hills as biome, and the surface is on Y=237. But with the new snow system on mountains, it is snowing in my testworld and it is freezing all my water. So could Mojang please make the game so that it doesn't have to snow in flatworlds.
Snow in Extreme hills biomes at high elevations is intended. If you never want snowfall in your testworld, just attach a pulser to a command block running the command "/weather clear".