Snowflakes come in different shapes and sizes, mainly because of differences in the temperature of the air and the amount of moisture that's present when they form. Flakes that form in wetter, milder environments tend to be fatter and more pronounced. Flakes that form in colder, relatively dry environments are smaller and lighter. A change of as little as a few degrees can make a big difference in size and shape. Colder flakes sometimes take on all sorts of strange shapes, too, from needles to a sort of barbell shape.