Snow Types
Looking at snow crystals and the bonds between them can tell us quite a bit about the snowpack and how stable it will be. Quite often, metamorphosed snowflakes become more closely bonded because of water refreezing and connecting crystals, but the more dangerous metamorphasis for avalanches is the formation of depth hoar, which is not a very cohesive snow layer.
From "A Field Guide to Snow Crystals" by Ed LaChapelle
Stellar Dendrite
Stellar
Plate
Column
Needles
Capped Columns
Above Images from http://www.its.caltech.edu/~atomic/snowcrystals/
This Image is from the WA "Snowflake" Bentley Collection, the classic original collection of snowflake photography. http://snowflakebentley.com/