The shape of snowflakes is influenced by the temperature and humidity of the atmosphere.
Snowflakes form in the atmosphere when cold water droplets freeze onto dust particles. Depending on the temperature and humidity of the air where the snowflakes form, the resulting ice crystals will grow into a myriad of different shapes.
Wilson Bentley (1865 – 1931) from Jericho, Vermont was the first person to capture photographs of snowflakes through the use of a microscope attached to a camera. His collection of 5,000 snowflake images introduced many people to the astounding diversity of snow crystals.
In 1951, scientists from an organization now called the International Association of Cyrospheric Sciences (IACS) devised a classification system that characterized snowflakes into ten basic shapes. These shapes include the stellar crystals that many people are familiar with and odd snowflake forms such as capped columns. The IACS classification system is still in use today although there are other more complex classification systems as well.
Kenneth Libbrecht, Professor of Physics at the California Institute of Technology, has made extensive observations of how water molecules get incorporated into snow crystals. In his research, he has observed that the most intricate snowflake patterns are formed when there is moisture in the air. Snowflakes produced in drier conditions tend to have simpler shapes.
Temperature also has a large effect on the formation of snowflakes according to Libbrecht’s research. Snowflakes formed in temperatures below – 22 degrees Celsius (- 7.6 degrees Fahrenheit) consist primarily of simple crystal plates and columns whereas snowflakes with extensive branching patterns are formed in warmer temperatures.
Bottom line: Temperature and humidity influence snowflake formation. The most intricate snowflake patterns are typically formed during warm and wet conditions.