minecraft-assets/assets/minecraft/blockstates/grass_block.json

{
  "variants": {
    "snowy=false": [
      {
        "model": "minecraft:block/grass_block"
      },
      {
        "y": 90,
        "model": "minecraft:block/grass_block"
      },
      {
        "y": 180,
        "model": "minecraft:block/grass_block"
      },
      {
        "y": 270,
        "model": "minecraft:block/grass_block"
      }
    ],
    "snowy=true": {
      "model": "minecraft:block/grass_block_snow"
    }
  }
}