[Alamo-Girl]

Thank you for your reply!

I'm sorry, you said external forces. I see no external forces mentioned.

Based on the physics described on the excerpt at post 2323, including the links to faceting and branching, the "external forces" involved in the formation of complex structures of snowflakes are: molecular forces on the lattice, diffusion of water molecules in the air and the primary causation for patterns: temperature and humidity.

For Lurkers: in post 2316, I contrasted this type of complexity to self-organizing complexity (from the link):

Self-organization is seen as the process by which systems of many components tend to reach a particular state, a set of cycling states, or a small volume of their state space (attractor basins), with no external interference.

[edsheppa]

molecular forces on the lattice

No, it is molecular forces within the lattice that are determinative. Replace the water with methane at the same pressure, temperature and concentration and you won't get methane snow crystals. The water molecules arrange themselves, all they need is the right environment.