Have you ever been outside on a cold, snowy day and actually tried to look at individual snowflakes as they drifted aimlessly by your head? Maybe you've tried to photograph them as they lay on the ground, plants, or your clothing? Regardless, each snowflake that falls differs depending on different properties of the atmosphere at the time, providing for that wintry scene outside.
How do snowflakes form though? Well, it takes a complicated process for a snowflake to actually reach the ground. First, in most cases, you need what is called an "ice nucleus", which is a particle that acts as a nucleus for an ice crystal to form around. These particles can be dust, pollen, soot, volcanic ash, and more. The second thing you need is the right temperature and relative humidity within the portion of the atmosphere that the snowflakes are forming in. This is of course the most important part, because it is based off of these variables that we get snow or not and what type of snowflake falls.
Now, we've all heard the very popular addage, "No two snowflakes are alike"...but is that true? The reason for this saying is because flakes can grow in so many different ways that it is possible that no two are the same. However, Nancy Knight, from NCAR (National Center for Atmospheric Research), has actually found two very similar snowflakes when put under a microscope. Therefore, next time you hear that saying, take it with a grain of salt, because out of the multitude of flakes that fall each winter, it is possible for two to be alike.
Above: Graph of snowflake types based on Temperature and Supersaturation (Courtesy physics.montana.edu)
The graph above provides an illustrative view of what different types of snowflakes temperatures and degrees of supersaturation produce. The horizontal axis has temperature, in celcius, and the vertical axis is measured in supersaturation, which is a measure of how saturated an air parcel is past 100% relative humidity. Below are a few types of snowflakes:
Plates
These forms of snowflakes are generally produced by relatively low saturation (drier environment) at most temperatures. Plated flakes are flat, and you guessed it, plate-like. They generally have six sectors, in a hexagonal shape, that have unique and symmetrical patterns.
Needles & Columns
Columns are hexagonal cylinders that are long in shape and hallow in the middle. Needles, on the other hand, are long and slender and look like small hair. They can create a dense snowpack, which could be conducive for avalanches. In general, these flake types are produced in relative warmer temperatures, with needles forming in high moisture environments, while columns are formed in drier air.
Dendrites
Finally, we get to dendrites, which are the most cliche of the types of snowflakes, which are depicted in any kind of wintry scene or decoration. They are produced in cold temperatures and high-moisture environments, producing a powdery snowfall. They have a large complex structure, with six symmetric and patterned branches, which can easily be seen to the naked eye as they fall and land.
