Snowflake

What is Snowflake?

A snowflake is a collection of ice crystals that form in the atmosphere and fall to the Earth as snow. These crystals typically exhibit a hexagonal pattern, with their specific size and shape determined by the temperature and the amount of available water vapor during their development.¹

When the air is humid, ice crystals grow rapidly, develop intricate branches, and clump together to form snowflakes. Conversely, in colder and drier conditions, the particles remain small and compact. The formation process generally begins around minute particles of dust or chemical substances floating in the air, except at temperatures below −40 °C, where crystals form directly from water vapor.¹

Why do snowflakes have a hexagonal shape?

The hexagonal shape of a snowflake is an outward manifestation of the internal molecular arrangement of ice. When water freezes, its molecules organize into a rigid, open lattice structure where oxygen atoms are joined in a series of hexagonal rings.²³⁴

This structure is driven by hydrogen bonding, which orients water molecules into a specific configuration. Because each of the hexagon’s internal angles is 120 degrees, this arrangement provides an unusually stable structure. As a snowflake begins as a small hexagonal plate, crystal arms grow from each of the six corners. If the corners are exposed to consistent environmental conditions, such as uniform temperature and moisture levels, these arms develop into the symmetrical, six-sided patterns commonly observed.⁴⁵²

How do avalanches form?

An avalanche is a rapid movement of material, such as snow, rock, or debris, down a slope. It occurs when material breaks loose from its surroundings and collects additional mass as it descends.⁹¹⁰

The formation of a snow avalanche depends on the interaction of four primary factors:

• Terrain: Avalanches typically occur on slopes of 30 to 50 degrees. Slopes lacking anchors, such as trees or large rock outcroppings, are more susceptible to instability.¹⁰
• Weather: Heavy snowfall, strong winds, rapid temperature increases, and rainfall on existing snow can create dangerous conditions. Wind, in particular, breaks down snow into crystals that form cohesive slabs and transports snow to lee sides of ridges.¹⁰
• Snowpack: Snow accumulates in layers that undergo physical changes over time. Weak layers beneath a cohesive slab can create the necessary conditions for a slide.¹⁰
• Trigger: Once conditions are unstable, a trigger—such as new snowfall, a falling cornice, or human activity like skiing—applies the force required to release the avalanche.¹⁰

What is the difference between snow, sleet, and hail?

Snow, sleet, and hail are distinct forms of frozen precipitation that differ in their formation processes and physical characteristics:

• Snow: Formed through the deposition of water vapor onto ice nuclei in cold clouds, snowflakes are aggregates of ice crystals that grow in a hexagonal pattern. Because they contain air pockets within their structure, they have a lower density than solid ice.¹¹¹²⁴
• Sleet: Also known as ice pellets, sleet consists of small, transparent, globular ice particles with a diameter of 5 mm or less. It forms when raindrops or mostly melted snowflakes fall through a layer of subfreezing air near the Earth’s surface, causing them to freeze before impact.¹¹³¹¹
• Hail: These are hard, spherical, or irregular pieces of ice with diameters ranging from 5 mm to over 15 cm. Hail forms in cumulonimbus clouds where strong updrafts repeatedly cycle ice particles through freezing and wet conditions, allowing them to accumulate dense layers of ice.¹⁴¹¹