Snowflakes come in a variety of shapes and sizes caused by differing temperatures and humidity levels in the clouds. There are stars, plates, columns, and needles in various forms, but almost all types are based on a hexagonal (six-sided) shape.
The most spectacular snowflakes, seen most often early and late in the winter, are the really big ones. Snowflakes are generally no bigger than a dime. But when the weather is a little above freezing (but below freezing in the clouds) and not very windy, it is possible for many snowflakes to stick together as they melt and then partially refreeze.
These stuck together snowflakes can be the size of half dollars or more. There is no good way to establish a record for the largest snowflake because they are in a state of melting as they fall, making official measurement difficult.
Meteorologist John Wheeler