ICE TREE RINGS. “A snowflake’s final shape is a history lesson of how the thing grew. The outside edge of the crystal is where it grew last, and as you go inward you can tell [the conditions of] where it was before”…temperature also plays a major role in the forming of flakes…shapes vary according to temperature.”
http://www.pbs.org/newshour/rundown/the-science-of-snowflakes/