The symmetrical but infinitely varied growth of snowflakes can be modeled by assuming that the rate of growth at corners relative to sides varies with atmospheric conditions that are essentially uniform over the size of one flake but may vary over time while the crystal is growing. But the details of how those growth rates depend on conditions are quite complicated and have long been an area of serious research by Caltech physicist Kenneth Libbrecht. Veritasium has produced a new video which includes some recent advances in Liebrecht’s work (in particular a more detailed explanation of why different temperature regimes favour columnar over planar growth or vice versa)