While to the naked eye falling snowflakes may have no discernible shape or design, in some cases up close they may reveal intricate patterns. Simply put, each type of snowflake is caused by variations in temperature and moisture content of the air.
These designs can range from the simple to the complex, and scientists have spent a good time researching why and how they occur. In this primer, the most basic snowflake formation concepts will be discussed.
Why is there so much variation in snowflake formation? No one knows for sure. "The growth depends on exactly how water vapor molecules are incorporated into the growing ice crystal, and the physics behind this is complex and not well understood. It is the subject of current research in my lab and elsewhere," snowflake researcher Ken Libbrecht says on his website.
Plates and Stars
At the warmest temperatures, generally above 28F (-2C), formation of snowflakes comes in the form of plates and stars. The types are directly related to the amount of moisture in the air. With high moisture content, stars form, which are flat objects that come in the shape that is most stereotypically associated with snowflakes.
As the moisture content in the air decreases, the snowflake loses its capability to form into more complex shapes, and returns to a more basic form called a plate. Typically these come in basic shapes which are quite plain.
Needles and Prisms
When the temperature falls below 28F (-2C) through about 14F (-10C), needles and prisms are the most predominant kind of snowflake. Again, moisture content decides the type of flake. At higher levels of moisture, the snow tends to form into long narrow needle-like structures.
This type can be the most dangerous in mountain areas, Dennis Randall writes for Family Education. "Needles tend to produce a dense, stiff snow pack which can produce an avalanche under the right conditions," he says.
At lower moisture levels, these needles become more column and prism-like. Hollow columns form at moderate moisture levels, becoming solid prisms in drier conditions.
Dendrites: The Most Complex Snowflake
Temperatures around 5F (-15C) with a high moisture level will produce some of the most beautiful snowflakes of all: the dendrite. This can be almost thought of as a star snowflake on steroids: unlike its flat cousin it comes in three dimensions.
The arms will radiate out from a central point, and take on elaborate shapes. Dendrites are the stereotypical snowflake, and are large enough to be seen by the naked eye. These types of snowflakes also make for the best powder for snow sports -- however cause of the cold temperatures needed it is rare to see in many areas other than the most mountainous ski resorts.
As moisture content drops, dendrites become flat once again, taking a more plate like shape, and become smaller.
Snow at the Coldest of Temperatures and Other Shapes
In below zero weather (-20C), moisture is at a premium. Thus, the capability to form complex snowflake formations is all but gone. At these temperatures, columns will appear when moisture content is high, with plates in drier conditions.
Besides the types discussed, there are a few other common types of snowflakes. Capped columns occur when a flake begins as a column and passes through an area of the atmosphere suitable for plate formation, while graupel forms when snowflakes come in contact with tiny water droplets come in contact and freeze to snowflakes, giving it the appearance of a tiny snowball.
