DISCUSSION: When it comes to looking at snowfall forecasts and snowstorms themselves, there are always many questions about why different snowflakes form and even when the same types of snowflakes are falling, why they may take on slightly different shapes. One classic example of this type of occurrence is when the most famous type of snowflake (i.e., dendrites) are fully part of a major winter storm. As shown in the picture above, which is one classic example of a stellar dendrite, they can be quite complex and stunning at the same time. However, there is much more that goes into how a snowflake forms the way it does and how complex the various outgrowth of the snowflake becomes as if all stored the surface of the Earth.
One such factor which has a major influence on the way in which a given snowflake such as the one shown above (courtesy of www.snowcrystals.com) will form is the variable moisture profile which is present through the depth of the middle to lower portions of the atmosphere. The reason for this is because whenever you have increased moisture in the presence of developing snowflake crystals, there is an increased potential for more accumulation of supercooled water and/or other nearby ice crystals onto the developing snowflake which can make them much larger or smaller depending upon the amount of water vapor available. In addition, whenever there is a lot more water vapor available within the depth of the atmosphere were the most snowflakes are forming (which is often referred to as the dendritic snow growth zone in atmospheric science terms), this can also allow snowflake generation processes to be much more effective and much more robust. Thus, when there is a greater presence of deeper lower to mid-level moisture content in the presence of a developing or mature snowstorm, there will often be much more efficient snowflake development as a storm wraps up and/or matures.
A second major factor which has a substantial influence on how and to what extent a given snowflake will form is the variable temperature profile through the depth of the middle to lower portions of the atmosphere. The reason for this is a result of the fact that when there is either a warmer or colder net temperature trend as this snowflake is going from its height of formation for the surface of the Earth, a snowflake can take on many different shapes depending upon the variable temperatures the ice crystal is exposed to as it is growing and developing during its path towards surface of the Earth. This reality is also reflected by the context of the second graphic shown above in an approximate sense since this is a rough approximation of the realistic temperature ranges for various case crystal types.
It is for these reasons that when people use the metaphor no two snowflakes are ever quite the same at any point in the world, this statement is completely true in every sense of the word. The reason is simply because as an ice crystal is following towards the Earth, the precise environmental conditions the ice crystal is encountering during its path downward will always be at least slightly different than the snowflake right next to it even at a very minor level. So, the next time someone uses the metaphor when there is a snowstorm or a threat of an upcoming snowstorm, you now have some real context behind that age-old phrase.
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©2020 Meteorologist Jordan Rabinowitz