Well, the problem with super-flat is that everything becomes plains biome.
You could do a customized world, tweak the parameters enough to get it flat.
Here is a thread discussing how to do this: how-can-i-generate-a-nearly-superflat-overworld
Then you could go to a biome where it rains at normal height (60-70) and starts to snows above a certain level.
If you want, here is a seed with that biome: 1364287100241175484
/tp 575 100 200
in creative and you are in a village in extreme hills+, it snows above 105.
I tried to tweak some parameters, but my computer/minecraft didn't like it, stuck at loading screen =/
I hope you can do better!