This question was asked by Hannah Faulkner:

“Why is every snowflake different?”

Response: Well, although there are dozens of different variables, not every snowflake is completely unique. There is a very small fraction of a chance, into the millionths, that you could find two identical snowflakes. At least, identical in the sense of looking at them through our own eyes. When you think about it, everything is truly unique at the subatomic level, with electrons constantly orbiting nuclei, everything is constantly changing, and it is nearly impossible for two items to match at the atomic level. So, in conclusion, with temperature, water impurities, atomic structure, and atmospheric conditions, matching snowflakes may not be impossible, but they most certainly are unlikely!