Dr Ken Libbrecht is the world expert on snowflakes, designer of custom snowflakes, snowflake consultant for the movie Frozen, and his photos even appear on postage stamps all over the world.
Libbrecht is a professor of physics at the California Institute of Technology (Caltech). A North Dakota native, Ken studies the molecular dynamics of crystal growth, including how ice crystals grow from water vapor, which is essentially the physics of snowflakes.
He has authored several books on this topic, including The Snowflake: Winter’s Frozen Artistry, and has a website with tons of information about the conditions and processes required for snowflakes / ice crystals to grow and form.
About a million billion snowflakes fall each second, averaged over a typical year. That's enough snow to make one snowman for every person on earth every ten minutes. (Of course, this is quite a rough estimate. The amount of total snowfall each year is not known well, nor is the average size of a snowflake.)
Recent estimates suggest that about half of the world's population has never seen snow close up. Most of China experiences some snowfall, but most of India and Indonesia do not. The equatorial regions of South America, Africa, as well as the desert regions of the Middle East, see the least snow on earth.