Is Snow a Solid or a Liquid? The Physics of Frozen Water

Snow is a solid. It is made of ice crystals, which form when water freezes or when water vapor changes directly into ice. Each crystal has a solid structure. A snowbank can also contain air and, when it begins to melt, liquid water between its crystals. That makes wet snow a mixture of phases, not liquid snow.

The confusion comes from snow changing as conditions shift. It can fall as ice crystals, collect on the ground, and later melt into water. To tell what state it is in, look at what is present: ice crystals are solid; liquid water flowing between them is meltwater.

Why snow is solid

In ice, water molecules form a repeating structure held together by hydrogen bonds. The molecules do not move freely past one another as they do in liquid water, so ice keeps its shape and resists flowing. Snow crystals share this structure.

Snow crystals often have six-sided forms. Their shapes vary with the conditions in which they grow, including temperature and humidity. The National Snow and Ice Data Center describes snow as precipitation made of ice crystals. A snowflake is therefore a collection of solid ice, not a frozen raindrop in every case.

Snow on the ground is usually a porous mass of crystals with air between them. That air makes fresh snow much lighter and less dense than a block of solid ice. It does not change the crystals from solid to liquid.

What makes snow feel wet

Wet snow contains ice crystals and liquid water. As snow warms, some of the ice melts. The resulting water can coat the crystals or collect in the spaces between them. The crystals remain solid until they melt; the water around them is liquid.

Temperature helps determine whether snow stays dry or starts to melt. Snow well below its melting point is generally dry. Near the melting point, liquid water can appear, though the amount depends on the snow and its surroundings. Packing snow can also change how it feels, but a snowball’s firmness alone does not establish whether it contains meltwater.

At standard atmospheric pressure, pure water freezes and melts at 0 °C (32 °F). This is a useful reference point, not a guarantee that every snowpack behaves the same way at a single air-temperature reading. Conditions within the snow and at its surface matter too.

One example: a snow crystal in a warm layer

Imagine a snow crystal falling through air that is below freezing, then passing through a warm layer near the ground. If the crystal melts completely, it reaches the surface as rain. If only part melts and the remaining ice refreezes before reaching the ground, it can arrive as sleet. If the precipitation becomes rain aloft and freezes on a cold surface, it can form freezing rain.

The outcome depends on the temperatures along the crystal’s path. A snow crystal that melts has changed from solid ice to liquid water. If that water freezes again, it returns to a solid state.

Snow, ice and liquid water

Snow and solid ice are both made of frozen water. The difference is in their structure as materials: snow is a mass of ice crystals with air between them, while a piece of ice is more compact. When snow melts, its ice crystals become liquid water, which flows and takes the shape of its container.

Water expands as it freezes, making ice less dense than liquid water. Snow also contains air between crystals, so its overall density is lower than that of solid ice. The amount of air varies with the snow’s condition; fresh, loose snow and compacted snow do not have the same structure.

Key Takeaways

• Snow is a solid made of ice crystals.
• Wet snow contains solid ice crystals and liquid meltwater.
• Air between the crystals makes snow porous and less dense than solid ice.
• Water’s standard freezing and melting point is 0 °C (32 °F).
• Snow can melt into rain or refreeze, depending on temperatures along its path.