I know there are large and small snowflakes-is there a science behind this?
Yes...and not only are there differences in the sizes of snowflakes, there are also differences in the shapes. In fact, it's generally accepted that no two snowflakes are exactly alike! Scientists who study such variations have found the two biggest factors that determine the size and shape of snowflakes (or ice crystals) are variations in temperature and moisture content of the region where the snow flakes form. That's why some snow flakes are shaped like 'fat' stars', others like thin-pointed stars, still others like six sided plates and others like needles or columns. Whatever their shape, all snow flakes form with six sides...a consequence of the way water molecules bond to each other. Take a magnifying glass the next time you're out in the snow...and 'catch' some snowflakes on a dark piece of cloth. See which shapes you see. My favorite website about snow is http://www.its.caltech.edu/~atomic/snowcrystals/