MSU Extension 4-H Environmental & Outdoor Education

Snowflakes form when water vapor in clouds freezes around a tiny particle like dust or pollen, forming a basic ice crystal. The dust, pollen or other particle provides the surface for the water vapor to attach to, creating what is called a crystallization nucleus – the foundation for a snowflake. As the crystal falls, it collects more water vapor from the air, which solidifies on its surface. But have you ever looked closely at an individual snowflake? Scientists who have studied snowflakes have determined that snowflakes form different shapes at different temperatures and that the journey of a snowflake has a big impact on its final shape.

Different qualities

Even if you haven’t looked at a snowflake under a microscope, you may have noticed that snow can have different qualities. Maybe you ran outside on a snowy day, excited to build a snowman or have a snowball fight, only to discover that the snow that fell the day before is not “good packing snow.” Or perhaps you’ve thought that the few inches of fresh snow in the driveway would be easy to shovel, only to find that it feels much heavier than you expected. It may seem like simply bad luck, but there are specific factors that create snow with these different traits.

Good packing snow occurs at temperatures that are just below freezing (30 degrees Fahrenheit or slightly colder). At this temperature, snow has a higher moisture content that allows it to stick together. Heavy snow also forms at warmer temperatures, which is why that last snowfall of late winter or early spring can seem to weigh a ton! This is because the warmer air is, the more moisture it can hold. At colder temperatures, snow is more likely to be powdery and easy to shovel, but not great for snowball fights. In addition to temperature, humidity, moisture and the path taken through the atmosphere all determine the qualities of the snowfall in your yard.

Different shapes

These same factors also dictate the shape of each individual snowflake. The snowflake thermometer pictured shows the shape of snowflakes at different temperatures. When most people think of snowflakes, they picture the stellar shape that occurs at the middle temperature ranges from approximately 10 to 30 degrees Fahrenheit. However, shapes can range from sleet and gravel at warmer temperatures, to hexagonal columns and pyramids at the coldest temperatures.

Humidity also plays a part, as higher humidity causes snowflakes to form more rapidly, resulting in more complex forms. The shape of an individual snowflake from its center outward can even tell the story of its formation and travel through the atmosphere. For example, a snowflake with a stellar shape at its center surrounded by a more solid hexagonal form was likely carried upward to a colder portion of the atmosphere before descending.

Learn more and explore

With so much snow falling each winter, Michigan State University Extension suggests these creative ways to learn more and explore the science of snow:

• Go snowflake hunting! When the snow starts falling, you can make a simple snowflake catcher using a piece of black felt. Cut the felt to the desired size (the size of a piece of paper works well) and staple it to a piece of cardboard for extra support. The black felt creates a great background for viewing individual snowflakes. Use a magnifying glass to take a closer look!
• Check the weather conditions on snowy days and make a prediction about the shape and quality of snowflakes before going outside with your snowflake catcher. Keep a snowflake journal throughout the winter to record these observations.
• Learn about “Snowflake Bentley,” the first person to photograph a snowflake in 1885. He dedicated his life to photographing and studying snowflakes (all the photos on the snowflake thermometer are his actual photographs).

With so many factors contributing to the formation of snowflakes, it is no wonder that we’ve come to believe that there are truly no two that are exactly alike.