I don’t have an opinion but I’ve been helping a professor whose research is all about lightning. Snow absolutely transfers charge, but the conditions are a bit less common. Lightning requires both liquid and solid water in the cloud to build the charge up. Most of the time the solid is higher up than the liquid, but for snow it the lower elevations are solid so you need a temperature inversion or something of the sort.
Partial pressure of water, actually – “relative” has nothing to do with it.
