I have seen experiments, where you fill a large glass with snow from the alps - and another with snow from the Rockies (US/Canada). When melted, there is only half the water in the glass from the Rockies - which is why it is powder-heaven for snow-freaks (such as myself).
I have no idea about the science - why it is this way.
[0] - https://en.wikipedia.org/wiki/Properties_of_water#Density_of...
There is a very wide range of snow. In particular, the heavy wet stuff acts and behaves very differently from "dry" snow -- whether that's light powder on top, or compacted, but dry, snow underneath.
Wet snow is increadibly heavy, and frequently contains or mixes with ice which makes removal (blowing, ploughing, shoveling, 'dozing) far more challenging.