Snow layers are incremented during snowstorms until they reach a full 8 layers. Snow next to full blocks stacks faster, making a smoother landscape. Snow stacking is related to the average neighboring snow height as well, again adding to a smoother landscape. Snow is less likely to accumulate next to non-cube blocks such as open space or fences. Source is available at https://github.com/CrazyCrafter-DoctorTee/SnowAccumulation
Feel free to use however you want, including in modpacks
WARNING: Forge 1.14.4 is currently in beta, and may cause issues!
*Images generated with faithful 1.12-rv3 as the resource pack and SEUS v11.0 as the shaderpack*