I did not know that about the snowflakes having six sides. I guess the two must have stuck together either as they were falling or when they landed on the hat. Most likely these were all hand held with an off camera flash, I can never seem to get my tripod in the right spot for where I try to do this.
I'm lucky to get at least one storm a year that meets my criteria for this. It has to be cold enough (in the 20s), actively snowing when I'm home and I have time to do it. Storms that roll in on a weekend that don't require lots of shoveling are ideal.