Snow is a hidden element that is not on the elements pane. Solid snow by default is the material YQ. Contact with Hot for the first time will cause Snow to be removed, melting into water, but this "snow-water" cannot be frozen back into snow. There is no way to get Snow from other elements, it must be selected with Y.
Contact with Water will cause Snow to begin to melt. The "melting" process removes the Snow element but leaves behind the Water, which melts more Snow furthering the melting process until all the Snow is liquid. Contact with Hot can provide the initial melt. The element Null is useful because it does not cause Snow to melt.
Melted pure Elemental Snow (the stuff you get from esc+Y+esc) closely resembles A-Type Null, because when the Snow is removed as it melts, it leaves behind nothing - Null.