What is clear ice?

Clear ice, as the name suggests, is clear, amorphous ice forming on surfaces as a result of water drops falling and freezing when the temperature is between 27 and 32°F (-3 to 0°C).

What is graupel?

Graupel—also known as snow pellets—is a funny word that means soft hail. It is created when supercooled water causes rime to form around a snowflake nucleus. Graupel is heavier and more granular than regular snow. Because of this, large amounts of graupel forming on a hill or mountainside can create dangerous conditions suitable for avalanches.

When does frost form?

A frost is a crystalline deposit of small thin ice crystals formed on objects that are at freezing or below freezing temperatures. This phenomenon occurs when atmospheric water vapor condenses directly into ice without first becoming a liquid; this process is called sublimation. Usually frost appears on clear, calm nights, especially during early autumn when the air above the Earth is quite moist. Permafrost is ground permanently frozen that never thaws out completely.

Frost coats a window with beautiful crystalline patterns.

Frost coats a window with beautiful crystalline patterns.

Besides rime frost, what other types of frost are there?

Different weather conditions can cause frost to form in various ways, sometimes with spectacularly beautiful results. The types of frost include:

Advection (wind) frost is frost that forms on the edges of plants and other objects. Advection frost is formed on the upwind side of objects during very cold winds.

Fern (window) frost gets its name from the fernlike patterns it forms on windows, especially windows that are not well insulated. Flaws in the glass's surface provide the nucleus needed for water vapors to form crystals, which then radiate outwards in intricate patterns.

Frost flowers are the result of a rare interaction between plants and the weather. When water inside a plant stem cracks or splits due to the cold, the water can escape and then freeze into flower-like shapes. Because they are so fragile, frost flowers usually break apart or melt within hours of forming.

Hoar (radiation) frost is formed on clear nights when surface objects are colder than the surrounding air. It appears as white, loosely organized crystals. Hoar frost may appear similar to rime, but unlike rime it is formed without the presence of mist or fog.

What is the difference between snow and hail?

Snow is water vapor that freezes in clouds before falling to the Earth. Hail is water droplets (raindrops) that have turned to ice in clouds.

How much water is contained in snow?

Depending on conditions—and as anyone who has had to shovel snow can attest to—snow can range from light and fluffy to heavy, dense, and slushy. As a general rule of thumb, however, every 10 inches of snowfall that accumulates on the ground would equal about an inch of rain if it all melted.

Is it true that no two snowflakes are exactly the same shape?

Some snowflakes may have strikingly similar shapes, but these twins are probably not molecularly identical. In 1986, cloud physicist Nancy Knight believed she found a uniquely cloned pair of crystals on an oil coated slide that had been hanging from an airplane. This pair may have been the result of breaking off from a star crystal, or were attached side by side, thereby experiencing the same weather conditions simultaneously. Unfortunately the smaller aspects of each of the snow crystals could not be studied because the photograph was unable to capture possible molecular differences. So, even if the human eye may see twin flakes, on a minuscule level these flakes are different.

When were huge snowflakes observed?

On January 28, 1887, in Ft. Keough, Montana, there was a snowfall that included flakes measuring a spectacular 15 inches (38.1 centimeters) across! Of course, these flakes were not individual crystals, but rather clumps of crystals sticking together to form large flakes. Not long after these stunning flakes were seen, Shirenewton, England, experienced a storm in 1888 where 3.75-inch (9.5-centimeter) snowflakes were seen.

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