It seems that the "Weather2" disables the "Primal Winter" mod's particles and fog effect. Is there a way to make them work together?

Weather2 takes control over all particles and the fog engine. Blacklist the "Primal Winter" mod in the Weather2 config, that should fix the particles. I'm not sure but I believe you can disable the ability for Weather2 to control fog also in the config, however that mean storms may look a little weird.

Thank you very much