Snowflakes
When does winter begin? The day the length of daylight falls below a predetermined number of hours, or the temperature sinks below a standard? The day of Winter Solstice?
Surprisingly, only the Winter Solstice, the astronomical event when the noonday sun has "moved" to stand overhead at the Southern Hemisphere's Tropic of Cancer has a definite winter start definition as far as I can tell. For me, I think of winter as being ushered in with the first snowfall that sticks to the ground for several days. And that sets the stage for this article.
Snowflakes. Perhaps, I should be more scientifically correct and title it: Snow Crystals. You see, although many people call almost any frozen precipitation - other than hail or sleet - a snowflake, meteorologists technically use snowflake only to refer to an assemblage of individual snow crystals that have remained fastened together during their fall.
Snowflakes typically form when near-surface air temperatures are not far from the freezing mark. At these temperatures, snow crystals are more "sticky," and those that collide together will adhere to one another better than at colder temperatures. At very cold surface air temperatures, they do not stick together well at all, and thus bitter-temperature snowfalls are mostly comprised of snow crystals.
Snow Crystals
Snow crystals are formed of ice molecules and are typically 0.5 to 5 millimetres (0.02 to 0.20 inches) in size. Snowflakes are typically bigger - generally about 10 mm (0.4 inches) across and perhaps as large as 20 to 40 mm (0.79 to 1.57 inches). Exceptionally large snowflakes can exceed 50 mm (2 inches) and aggregate hundreds of individual crystals. For a snowflake to grow exceptionally large, however, conditions must be perfect. Besides ideal temperature needed for stickiness, large flakes usually only grow when winds are light; otherwise the large flakes will break up as they fall.
The biggest snowflake reportedly measured 15 inches (38 cm) across and fell on January 28, 1887 at Ft Keough, Montana. Another giant fell in Bratsk, Siberia in 1971, a flake 20 cm (8 inches) by 30 cm (12 inches). Two decades earlier, residents of the English town of Berkhamsted saw snowflakes big as saucers, almost 13 cm (5 inches) across.
We think snowflakes, or more correctly snow crystals, are six-sided, frilly stars and are fairly flat like a pizza. Snow-crystal structure, however, takes on many forms. Besides the six-armed stars that look like frozen lace, there are a variety of shapes from flat hexagonal plates to three-dimensional small hexagonal pillars with hexagonal plates lying on each end, popularly called cufflink crystals. Other snow crystals resemble Dorian
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