In aviation Met terms light/medium/heavy snow is a measure of how fast it is falling not how much is accumulating.
The definition of heavy snow varies with temperature, visibility and day/night.
Daytime, <= -1c and vis <=400m
Daytime, > -1c and vis <=800m
Night, <= -1c and vis <=800m
Night, >-1c and vis <=1200m
All the above define Heavy snow.
For the full tables see page 49 in
https://www.faa.gov/other_visit/avia...overTables.pdf