January 28, 2026, the day after two snow days in a row, I was late to school. With many streets being narrower, cars commuting slowly and the appearance of many new potholes in Riverdale, the commute took longer than I thought. Rushing to my first lesson, History, I almost slipped on my shortcut along the quad at Fieldston. A thin layer of ice had formed, and every step felt uncertain. After catching my balance, I started wondering, why is ice actually slippery?
Later, I noticed that the cleared paths covered with salt were very safe to walk, even to run on, while the surrounding snow remained frozen. With additional online research, I found that these everyday winter experiences reveal very interesting scientific processes. From the physics that makes ice slippery and produces plenty of potholes on the streets after it gets warmer, to the chemistry of road salt and the atmospheric science behind snowflakes and winterstorms, the science of snow and ice explains much of what we experience during cold weather.
One reason ice is slippery comes from the unique characteristics of water molecules at its surface. Even when temperatures are below freezing, the very top layer of ice can partially melt, creating an extremely thin self-lubricating film of liquid water/disorganized water molecules ranging from one molecule to a few nanometers thick. This is a natural stable state of water molecules on the ice surface that tries to maximize hydrogen bonds. When you step on ice, pressure and friction from your boot and body weight will increase this effect, further melting a tiny layer. For that reason, scientists describe ice as having a thin “quasi-liquid” layer that exists even below freezing temperatures, which explains why the surface feels smooth and slippery. As liquid water reduces friction, my shoe did not grip the surface well, causing me to almost slip.
The salted pathways on the quad show another important principle of winter science: freezing point depression. When salt is spread on icy surfaces, it dissolves into sodium and chloride ions that mix with the thin liquid layer on top of the ice, disrupting the ability of water molecules to arrange into a solid crystal lattice. This solution freezes at a lower temperature than pure water, which means the ice melts even when the air temperature is still below the freezing point. Fun fact: the lowest temperature NaCl water solution can remain liquid is about -21 °C. As a result, the ice on salted streets in the winter breaks apart and melts into salty water that is much less likely to refreeze. That is why roads and sidewalks treated with salt remain clearer and safer to walk on during winter storms.
Understanding ice and salt leads to the larger question of how snow itself forms. This winter brought particularly heavy snowfall in many parts of the U.S. because of several atmospheric factors working together, as was predicted by Shuang-Ye Wu, Professor of Geology at the University of Dayton, already last summer. Meteorologists point to the behavior of the jet stream, a fast-moving river of air high in the atmosphere that guides storm systems. During the winter, the jet stream often dips southward, which allows cold Arctic air to move into the U.S. and creates the conditions necessary for snowstorms. At the same time, warmer ocean temperatures increase evaporation, which allows the atmosphere to hold more moisture. When that moisture meets cold air, it can fall as heavy snow rather than rain, as it did this year. Snow begins in clouds when water vapor freezes around tiny particles of dust or pollen in the atmosphere.
Try melting snow in a glass, and you will see the tiny “dirt” particles swimming in water later on! A snow crystal appears when water vapor in the air converts directly into ice without first becoming liquid water. As these ice crystals grow in a centrifugal pattern, they develop the intricate and beautiful shapes we recognize as snowflakes. The exact form of each snowflake depends on the temperature and humidity of the air as the crystal forms and falls through the cloud. Because these conditions constantly change, snowflakes grow in complex branching patterns, which is why no two snowflakes are exactly alike. Many snowflakes display six-sided symmetry because water molecules arrange themselves in a hexagonal lattice when they freeze. Snow is an important part of Earth’s climate system. Large areas of snow reflect sunlight into space, helping regulate global temperatures. In addition, the seasonal snowpack acts as a natural water reservoir that gradually melts in spring and feeds rivers and ecosystems. Because of these roles, changes in snowfall patterns can have important environmental consequences.
Winter weather also affects infrastructure in ways that become visible once temperatures start to rise. As the weather warms after a snowy period, potholes often begin to appear on streets. This happens because water from melted snow seeps into small cracks in the pavement. When temperatures drop again at night, the water freezes and expands because water expands by about 9% when it freezes, and the pressure widens the cracks in the road surface. Repeated cycles of freezing and thawing weaken the pavement until sections break apart under the weight of cars, creating potholes. This freeze-thaw cycle is common in climates with fluctuating winter temperatures and is a major reason why road damage becomes noticeable in late winter and early spring.
Though I almost fell while running along the quad, I learned a lot about the science involved in the formation of snow and ice. The slippery properties of ice that almost made me fall exist because of its “quasi-liquid” superficial layer that forms even below freezing. In contrast, the salted paths around Fieldston stayed safe to even run on because salt lowers water’s freezing point and prevents ice from forming. Even the potholes result from the same winter processes as meltwater seeps into cracks in the pavement and repeatedly freezes and expands during freeze-thaw cycles, which made me late in the first place.
