If you build a 1x1 tower in snowy biomes and build until y=93 then set weather to rain, It will snow on top of the tower but not other areas. Also, if you stand directly above the 1x1 tower, you'll no longer see it.
Steps to Reproduce:
1. Build a 1x1 tower until you reached y=93
2. Use /weather rain
3. The snow will appear and if you break the topmost block the snow will no longer appear
This is supposed to happen in cold biomes, and you not seeing the snow is also normal. The reason why its snowing on that block is because its at the level where it starts to snow, while the other areas are too low to produce snow. I know mountains and they behave like this.