Why is Every Snowflake Unique?

2018-12-01 10:17:17.000 – Chloe Boehm, Summit Intern

Since the summit has seen 110” of snow since the start of the snow season (July 1^st) and 58” during the month of November alone, I decided to take this opportunity to look all this snow in a little bit more detail. Most of us have probably heard the expression “unique as a snowflake” derived from the fact that each snowflake is, in fact, unique. The size, structure and overall physical appearance of each snowflake differs. But why? To answer this question, we have to go back and discuss how snowflakes are formed.

Snowflakes form when very cold water droplets freeze onto a pollen or dust particle in the atmosphere. This particle becomes an ice crystal which as it falls to the ground, get larger as additional moisture freezes onto it. The temperatures at which an ice crystal forms combined with the humidity of the air determines the basic shape of the crystal. This in turns means that the overall shape of snowflakes greatly depends on the atmospheric conditions at the time of formation. The graphic below expands on this concept showing conditions necessary for different types of snowflakes.

Graphic showing the effects of temperatures humidity on snowflake formation. Image via Kenneth Libbrecht.

As you can see, snowflakes formed in very cold conditions are normally simple crystal plates and column while warmer temperatures produce snowflakes with more intricate branching. The most popularly photographed snowflakes, called Dendrites, need fairly warm and wet conditions to form. There is actually an area of the atmosphere called the dendritic growth zone, or DGZ, which is a zone where the air temperatures is roughly between -10 and -20 degrees Celsius. It was given this name because looking to see if the air is saturated in this zone will give a good sense of where snowflake development is occurring. Although snowflakes can form in temperatures above or below this temperature range, their shape will stray away from what most people would consider a traditional snowflake.

So getting back to our original question, why is every snowflake unique? The DGZ is high up in the atmosphere, usually at least 14,000 ft above sea level. That means that the recently formed snowflakes have a long way to travel before you see them. As these snowflakes are traveling towards the ground, they are picking up additional moisture to add to their structure. The path that each snowflake takes is unique with ever so slightly different atmospheric conditions. All it takes is the slightest change in temperature or humidity to alter the structure of a snowflake. Therefore, each snowflake tends to look unique!

Next time you are outside exploring in the snow, see if you can identify the types of snowflakes you are seeing and what that means for the conditions of the atmosphere above!

Chloe Boehm, Summit Intern