Does anyone know how these rain sensors work? Is it optical or some sort of moisture sensor? A combination of both?
I'd say for the system to detect snow reliably that it would depend on the snow and what type of sensor is used to detect it. A heavy wet snow should be easy to detect. I light dusting of 'dry' very cold snow would be more difficult to detect.
It's an optical sensor and it's also used by the auto light feature.