Snowing on only one block.

Basically I built a house, and on only one tiny part of the front of the roof, it was snowing with rain completely surrounding it.

What I expected was there to be rain all around me.

There was one tiny part, with snow surrounded on all four sides with rain, unless I put blocks there, and if I flew up a bit, it started to snow completely on top of the rain. (At one y-axis was rain, flew up a bit and it was all snow.
Steps to Reproduce:
1. Build an upside down "W" in a mountain up to where it starts to snow
2. Make it rain
3. Watch how there is snow