In winter we can still find beautiful moments taking place around us. One of these beautiful moments is a snowflake! Its common knowledge that each snowflake is unique, but a single snowflake can tell us a lot about what is happening in the atmosphere around and above us. Why are some snowflakes smaller than others? Why does snow sometimes fall when it’s above freezing?

Snow needs moisture and humidity to form, so very dry places will not accumulate snow even if it is below freezing. This includes areas of Antarctica. Since warmer air holds more moisture, it tends to be less humid the further the temperature falls below freezing. Snow is formed simply by the combination of ice crystals in the atmosphere combining until they become so heavy that they fall to the Earth.

When the air temperatures are warm enough in the atmosphere, the snowflakes melt a little around the edges, combining in the air before reaching the cooler layer below. Once they fall down into a colder layer of air, they refreeze and form large clumpy snowflakes. In order for this to happen there has to be a layer of warm air in the atmosphere between the clouds and the ground for the snowflakes to fall through. Otherwise the snowflakes will not combine and they will stay relatively small.

Snow requires the air in the atmosphere to be below freezing (0°C or 32°F), but the air near the ground surface does not need to be at freezing. In order for snow to accumulate, the ground needs to be less than 41°F. This is because the snowflakes have the ability to cool the air around them through evaporative cooling. This is when heat energy is taken out of the air around the snowflake to produce the melting. So if it is balanced just right, this process can cool the air enough to actually stop the snow from melting once it hits the ground.

There are many signs in our environment that clue us in to what is happening around us. Even a simple little snowflake has a story to tell.

Sam Nunes is Environmental Educator at Woodcock Nature Center. For information, visit woodcocknaturecenter.org.