Snow plow’s coming!” I hollered as the unmistakable rumble of the yellow behemoth pushed another small mountain of snow into the entrance of our short dead-end street. There it stopped, adding to the mound of icy, dirty snow that had blocked our lane for weeks. By now the mound had grown to an impressive height of ten feet, an object of awe to neighborhood kids, and one of frustration to my parents who had to scale this glacial mass to reach our car parked up the street. It was 1960 and I hadn’t seen the inside of my classroom for more than three weeks.
The twenty years between 1960 and 1980 gave birth to some remarkable winter storms that hammered Virginia. In 1960 alone record snow fell—and stayed! From the southern Highlands to Northern Virginia repetitive snow, sleet, and persistently cold temperatures resulted in snow accumulations on a scale rarely seen in the Old Dominion.
Four back-to-back storms from February 12 to March 8 disrupted commerce, closed schools, and made life miserable in general for millions of residents from the southern Appalachians to the Northeast. Record cold threatened to overstrain our furnace, snow accumulated alarmingly on roof, and we had long given up trying to reach our woodpile when the power blinked off, leaving us without heat and in the dark for hours.
Having moved to Northern Virginia two years earlier from California, we had no way of knowing this winter was extreme. The first flurries of December were just harbingers of the snowstorms to follow. By early March all we saw was a landscape swathed in white as the fourth storm bore down upon us. My mother groaned but I was excited and, grabbing my scrap of black felt, ran outdoors.
As an only child trapped indoors by the weather, I created my own entertainment. In 1960 there was just three network channels airing game shows and soaps—not exactly stimulating for a thirteen year old. I read, listened to my transistor radio, talked on the phone, worked jigsaw puzzles, and when the sun did come out, played outdoors with my collie. And I enjoyed my new microscope, a recent Christmas gift. What I saw now was truly magical—snowflakes!
As flakes the size of butter chips fell, I captured them on my felt, dashing indoors to view them under the microscope. No two shapes were alike and as I examined these iconic symbols of winter, I had no way of knowing that scientists have been fascinated for centuries by them as well. Snowflakes are a mystery!
They are fleeting works of art; one second a perfectly formed six-sided star and the next minute reduced to its most elemental form—water. Snowflakes are made of ice, flecks of ice that tumble down from the clouds. A snowflake forms when water vapor in the air condenses into solid ice. As more vapor condenses onto a nascent snow crystal, the crystal begins to grow, often developing elaborate patterns.
As the ice crystal falls, tumbling from one part of the cloud to another, it encounters changes in temperature and humidity that affect its structure. By the time it settles to the ground it may have experienced a complicated set of variables that ultimately affects its appearance. A snowflake may be a single ice crystal, a few crystals stuck together, or hundreds of crystals melded together forming large puff balls that float gracefully down from the sky. And since no two crystals form or fall alike, they all look a little different.
Temperature plays a major role in determining snowflake shapes and sizes. The quintessential snowflake depicted on holiday cards and wrapping paper, called a stellar dendrite, is the most familiar to snowflake lovers, but a fascinating array of shapes and sizes that one might not associate with a snowflake are equally fascinating and beautiful--plates, dendrites, needles, hollow columns, or bullets, all dependent on the right conditions.
Within a cloud there are also variations in humidity as well. The higher the humidity the faster the crystal grows, putting out intricate facets and branches. As long as the humidity remains high, the crystal continues to grow. When its weight is sufficient, gravity pulls it to the ground in the form of snow. Ironically snowflakes fall when it snows but not all snows produce well-formed snowflakes.
The type of snow that falls is determined by the shape of the flakes, the rate of accumulation, and how the snow collects on the ground. From about freezing to 25ºF snow forms as flakes. When temperatures fall to about 23 ºF the snow forms into needles; a degree lower and it becomes hollow columns. Below 10 ºF flakes start forming again, but when it drops to -8 ºF it turns into columns once more. At -30 ºF snow stops forming altogether. Despite 75 years of research, scientists still don’t know why.
Scientists first wrote about snowflake morphology as early as 1611 when mathematician Johannes Kepler published a short treatise on snow crystals, noting their six-sided symmetry. French philosopher and mathematician René Descartes was the first to pen a reasonably accurate description of snow crystal morphology, speculating that their variability might be due to their location within the clouds. The invention of the microscope in 1590 enabled English physicist Robert Hooke to publish a volume of snowflake sketches he noted under his microscope, illustrating the complexity and symmetry of various ice crystals. But it would be the camera that would bring snowflakes to the world.
Wilson “Snowflake” Bentley was born in Vermont in 1865. Like many children he was fascinated by snowflakes and, over the years, tried to draw what he saw through his microscope. But complex snowflakes were difficult to draw in detail before they melted, so he attached a bellows camera to a compound microscope and, after much trial and error, photographed his first snowflake in 1885. In his lifetime he would go on to capture more than 5000 snowflake images and for the first time others could see what Bentley referred to as “tiny miracles of beauty”.
Japanese physicist Ukichiro Nakaya was the first to grow artificial snow crystals in the laboratory, observing, identifying, and cataloguing crystal morphology under various environmental conditions. Nakaya’s work was published in 1954 in a beautiful book entitled Snow Crystals: Natural and Artificial.
In his footsteps, Dr. Kenneth Libbrecht, professor of physics and head of the physics department at Caltech is the leading expert in his field of the mechanics of crystal growth. Dr. Libbrecht has spent much of his career satisfying the public’s endless fascination with snowflakes. Traveling the globe, he captures images of natural snowflakes, then recreating them back in his lab.
When temperatures are optimal and snow begins to fall, he captures flakes on a piece of blue foam board, looking for good crystals. Well formed crystals are picked up with a paintbrush, placed on a glass slide, and mounted on his microscope to photograph.
Growing up in North Dakota Libbrecht had an ample source of material to observe and concluded that “if you live in snow country you ought to know a little bit about what’s falling from the sky.” He found the physics of ice crystal formation infinitely fascinating and wanted to share it with others. In 2006 his snowflake photos graced more than 3 billion US postage stamps and he has published numerous books and field guides on the subject, most notably his book Snowflake.
The Weather Channel recently announced it will begin naming significant winter storms similar to those assigned
to hurricanes. The first three will be Athena, Brutus and Caesar. According to TWC, these will apply to “storms with an attitude”, capable of “producing disruptive impacts including snowfall, ice, wind and temperature and whether the disruptive impacts will affect a populated region and occur at a particularly busy time of day or week.”
When storm #4 ended March 9, 1960, the snowfall had frozen into a crust several inches thick that held my weight. As my collie and I walked precariously on its surface, the snow came within six inches from the top of our 54" high chain link fence. We stepped over it easily and marveled at a world turned sparkling white. I would have to wait until next winter to capture snowflakes again for my microscope but, quite frankly, I had had my fill of snow for awhile!