How Does Snow Form?

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Snow is defined as solid precipitation. Snowflakes are tiny ice crystals with temperatures below 0° C (32° F). These crystals are created in the atmosphere by absorbing water droplets. When they collide, they bond together and form snowflakes. Snowing occurs when many crystals come together and become heavy enough to fall to the ground due to Earth’s gravity.

Snowflakes are about one centimeter (0.4 Inch) long and can have many shapes. They can have the appearance of a prism, hexagonal plates or the mythical stars that we draw whenever we want to represent a snowflake.

Snow crystals to categories.
Crystallography has been categorizing snow crystals into various categories according to their atom disposition

For snow to form, two essential conditions must be met:

  1. Temperature must be at or below freezing (0 degrees Celsius or 32 degrees Fahrenheit).
  2. There should be a minimum amount of moisture in the air.

If these two conditions do not occur, snow will not be formed. Because snow formation requires moisture, very cold but very dry areas may never receive snow. For example, the Dry Valleys of Antarctica, where there is ice, but no snow.

At What Temperature Snow Is Formed?

There is a myth that negative temperatures are always necessary for snow, but this is not the case. Precipitation falls as snow when the air temperature is below 2° Celsius. However, warmer air can hold more water vapor. That’s the reason why most heavy snowfalls occur when there is relatively warm air near the ground, typically -9° C (15° F) or warmer.

If the temperature is above 2° C (35.6° F), the snowflake will melt and fall as sleet or rain, instead of snow.

The Difference Between Wet Snow and Dry Snow

The size and composition of a snowflake depends on how many ice crystals clump together to form it. This will be determined by the temperature and relative humidity of the air. Snowflakes that fall through cold, dry air will be small dusty flakes that don’t stick to each other. This dry snow is ideal for snow sports, but is more likely to be blown away by the wind.

However, when the temperature is slightly above 0° C, the snowflakes melt around the edges and stick together to become large, heavy flakes. This creates wet snow that sticks easily and is great for making snowmen.

Types of Snow

In mountainous areas different types of snow can be detected. The type of snow mainly depends on altitude, exposure, temperature, humidity, wind and orography. Ski resorts use standardized terms to describe their snow conditions.

Powder Snow

Powder is freshly fallen, uncompacted snow. The density and moisture content of powder snow can vary. Snowfall in coastal regions with higher humidity is usually heavier than in arid or continental regions. Light powder snow is prized by skiers and snowboarders because it creates a pleasant sensation of floating. It is often found in the Rocky Mountains of North America and in most regions in Japan.

Crusted or Frozen Granular Snow

This type of snow occurs when the water molecules located in the upper layer of the snow freeze and form a solid layer. If a surface icy crust is soft and thin, it is possible to cross it without difficulty. However, if it is thick, it will make skiing more complex.

Sleet or Spring Snow

Sleet snow is a coarse, granular snow, subject to freeze-thaw. Basically, it is snow with a high moisture content. It’s not the most pleasant snow for skiing. If you go on vacation at the end of the season, you are likely to find this type of snow.

Crud Snow

It is a heavily tracked snow which melted and then froze again to leave a deeply rutted surface. This phenomenon is also called frozen compacted snow. For safety reasons, it is advisable to avoid skiing or sliding on these types of surfaces.

Artificial Snow

Ski resorts produce artificial snowfall using snow cannons when it does not snow naturally. Artificial snow is denser due to the spherical shape of the flakes, but it is possible to produce snow of different qualities. The ratio between temperature and humidity, determine the quality of the snow produced. It is a technology that offers an extraordinary quality of snow that is almost indistinguishable from natural snow.

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