Looking at snowflakes is more than simply a pleasant pastime: the shapes and structure of snow crystals tell us a great deal about the conditions under which the crystal formed: How cold? Did the crystal growth occur in more than one temperature regime? How moist were the conditions? Did the crystal fall through cloud after it formed, or did it fall mainly though clear air? These are a few of the things that can be learned by studying snow crystals.
Because we've received some questions about this, we decided to make an out-of-print snowflake identification manual ( 1.5 MB) available online. Simply click the link and you will be able to see (and save) the manual in PDF format. (If you don't have the Adobe PDF reader, it's available as a free download here .)