It could maybe look like:

{
  "type": "lithostitched:add_feature",
  "dimension": "minecraft:overworld"
  "climate":  {
    "temperatureMin": 1.0,
    "temperatureMax": 2.0,
    "downfallMax": 0.25,
    "has_precipitation": true
  }
}

Being able to have a min/max range would make it pretty flexible. A biomes field could be used as a whitelist/blacklist too.

like the idea of climate-based biome targetting, would probably look different format-wise though.