This answers it: https://www.reddit.com/r/askscience/comments/5gae8u/why_are_snowflakes_flat/daqoh6o/ https://www.reddit.com/r/askscience/comments/5gae8u/why_ar

This answers it: https://www.reddit.com/r/askscience/comments/5gae8u/why_are_snowflakes_flat/daqoh6o/ https://www.reddit.com/r/askscience/comments/5gae8u/why_are_... "Ice crystals are like a six-sided prism. This prism grows as more ice molecules stick to its faces. It turns out that under conditions found in common snowstorms, some facets in XY plane tend to grow much faster than the facets along the main axis of the crystal. As a result, snowflakes usually end up looking like flat pancakes with many finger-like branches"