A computer model of a randomly-generated origami snowflake that should be similar to Wilson Bentley's observations.
Load up the OpenSCAD file (snowflake.scad), compile and render. If you don't like the look of the snowflake, recompile and try again. When you see something you like, look at the beginning of the compile output and it will have a seed number. Set this as the variable 'rs'.
Consider using openscad to generate files, rather than the pre-generated STL files, because it will make your snowflakes a bit more unique:
openscad snowflake.scad -o random_flake.stl
Snowflakes will be randomly generated based on a few customisable parameters. For a less dense snowflake (more skeletal), reduce the number of crystals (nc). For a more dense snowflake (more like a hexagon), increase the number of crystals. For more variation in crystals, increase the crystal max thickness (cmt). Other parameters are present, see the top of the file for more details.
I have tried to keep the placement of crystal seed start points fairly uniform across the flake (square root function to account for variable area across a triangle), and crystal angles are limited to 60 degrees (as seems to be the case from Wilson Bentley's pictures).