  We motivate and derive the dynamical rules for a computationally feasible
three-dimensional cellular automaton model of snow crystal growth. The model
improves upon points of weak physical connections identified in other similar
models which have produced morphological features observed in many snow crystal
photographs. A systematic survey of the morphologies resulting from our model
illustrates the degree to which these features persist in our results, and the
trends that appear as model parameters are varied.
