First one flake. Then another. Then a new world.
Snow beckons everyone outside to play and explore. A good snowfall is a chance to throw snowballs, build forts, spot animal tracks, and notice how white highlights outline the shapes of trees, says Tifanie Treter, who often teaches about snow in Winter Science Camps at The Morton Arboretum.
She suggests catching snowflakes on a dark piece of paper to examine their shapes, laceworks of crystals that began as droplets of water vapor freezing in the upper atmosphere. As they fall toward the earth, the tiny ice crystals collide and stick together in regular, intricate designs, usually with six sides.
But snow is not mostly ice; it’s mostly air, trapped in the spaces of the lacework. On average, snow is about 10 percent frozen water and 90 percent air. That makes it a good insulator, like a comforter. Instead of freezing plants and animals, it actually protects them against bitter cold and drying winds. Small animals such as voles tunnel through the snow so hawks and foxes can’t spot them.
Good snowball snow, heavy and moist with big flakes, forms when it’s not too cold, right around freezing at 32 degrees. That’s because warmer air can hold more moisture. Colder air means drier snow with smaller flakes.
“Time on the ground can change snow,” Treter says. The weight of a deep snow compresses the lowest levels, creating layers with different densities. As snow melts, it provides water that soaks into the soil and helps plants grow in spring.
Families can make the most of a good snow with a hike in the Arboretum woods, or rent snowshoes or skis. Treter suggests bringing a sketchbook to capture the shape of a tree outlined by snow. “It takes on a different personality,” she says. A camera, a magnifying glass, and a field guide to identify animal tracks will add to the fun.