http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/1288431-just-another-spawner-jas-v0-14?comment=2099

would it be possible to add a check for rain/weather?

Precipitation is easy.

Snow versus rain versus desert clouds seems impossible. Or need to study if further and suggest a forge hook.

would it not work to combine precipitation with biome dictionary type, since SNOWY covers snow. Does DRY not cover no precipitation?

That is implied by vanilla biomes; but its not required. Its a good and simple hack though.

Precipitation knowledge exists within MC as the renderer knows whether to rain or not or snow; its a question of getting access the relevant variables.

actually... I wonder if such a hook would help Corosus with his Local weather and storms mod. The existing 'is raining' flag being global is a problem for him also.
.. I take back my prior discouragement. This would be a handy thing to have