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Courtesy of SnowCrystals.com
In winter, Montana and Wyoming dish out fierce weather and fearsome beauty. Snow and cold transform the outdoors into a winter wonderland, but they also create danger, drama and dread.

In winter, Montana and Wyoming dish out fierce weather and fearsome beauty.

Snow and cold transform the outdoors into a winter wonderland, but they also create danger, drama and dread.

Here’s a look at some of the science of winter — from the chemistry of snowflakes to the physiology of hypothermia and the physics of avalanches.

When it comes to white fluffy stuff, Montana has one flaky claim.

The world’s largest snowflakes hit the ground during a January storm in 1887 at Fort Keogh, on the western edge of Miles City.

At least that’s what’s listed in the Guinness World Records.

A rancher described the snowflakes as “larger than milk pans” and measured one at 15 inches wide.

A mailman, stuck in the blizzard, also witnessed the huge flakes, although their claim lacked tangible, corroborating evidence.

Other challengers don’t even come close to dethroning the Miles City behemoth.

Weather officials in Berlin, Germany, reported a storm in 1915 that produced 4-inch-wide flakes shaped like oval bowls, and a fall snowstorm in Laramie, Wyo., in September of 1970 dropped 3-inch-wide flakes.

While it’s tempting to blow off the record-breaking flakes as a tall tale, Kenneth G. Libbrecht, a physicist with a passion for snowflakes, believes in at least the possibility of pan-sized snowflakes.

“It’s not an individual snow crystal — it’s gobs of snow crystals stuck to together,” said Libbrecht, who heads the physics department at the California Institute of Technology in Pasadena, Calif.

It’s hard to believe in softball-sized hailstones, but people pull them out of their freezers, he said.

Libbrecht created the Web site SnowCrystals.com, which includes online photo galleries of snowflakes along with the science.

While Southern California may seem like an odd place to develop a penchant for snowflake photography, Libbrecht grew up on a farm near Fargo, N.D.

“All sorts of things fall out of the sky, and most people don’t even stop to ever look at them,” he said.

Beautiful, symmetrical, photogenic snow crystals are surprisingly hard to find. Before finding a picture-perfect one, Libbrecht sometimes culls through thousands of misshapen crystals. Many snowfalls yield nothing but small, sand-like flakes.

Temperature and the amount of moisture in the air determine a snowflake’s basic shape. Scientists describe those shapes using names such as columns, needles, plates and dendrites.

“One of the categories I like best is capped columns,” Libbrecht said.

“They’re really odd-looking. They’re the kind of things you never see if you don’t know they exist and don’t go out looking for them. As a physicist, I like them because it’s a little hard to explain how they grow.”

The capped columns, which look a bit like two wheels on an axle, start growing as columns, then grow into extremely thin plates on each end.

Why snowflakes change into different shapes at different temperatures is a question that has puzzled scientists for at least 75 years.

“It’s a fascinating puzzle,” Libbrecht said. “It’s not a question that’s vital for survival, it’s like a scientific Sudoku.”

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The perfectly formed, star-shaped snowflakes people like to draw or knit on ski sweaters are called stellar dendrites.

Checking the temperature can aid in the search, said Garon Smith, a chemistry professor at the University of Montana.

One way to examine flakes is to catch them on black construction paper or a felted board and look at them outdoors under a magnifying glass.

“Stellar dendrites grow best between 15 degrees and 5 degrees,” Smith said. “That’s a good time to go out and find some really nice snowflakes.”

When moisture is abundant, conditions are right for the point growth to develop into the six-fold symmetry, Smith said.

The points of a stellar dendrite start off growing pretty fast, and then they slow down just a bit as they move through drier air. The ends of each point start to look like half of a hexagon, with three little points.

If the flake passes through moister conditions again, each point starts to grow.

Snowflakes typically form around a little spec of particulate, a teeny droplet of something such as soot or pollen grains. As the flakes get thrown around in circles up in the atmosphere, they run across moister and drier conditions.

“The snowflake is a history of all the various places they’ve been,” Smith said.

It’s true that no two snowflakes are the same, Smith said. At least it’s true for flakes large enough to see with the naked eye.

“That many molecules hooking on the same way, the chances are, it just isn’t going to happen,” he said.

It’s also true that it can get too cold to snow.

Snow is unlikely at very low temperatures, basically because not much water vapor is left in the air at that temperature, Libbrecht said.

“At minus 40, you’re not going to get any snow,” Smith said.

Frost is made up of minute ice crystals, which form on solid surfaces. Larger crystals are called hoarfrost.

“Some of the best hoarfrost I ever saw was in an outhouse back on the farm,” Libbrecht said.

It was growing in the cold, moist environment on the underside of the toilet seat.

Light glinting off faceted ice crystals of surface hoar can make snow banks seem to sparkle.

Surface hoar typically forms when the snow bank warms up during the day and chills down at night, causing water to evaporate from inside the snow bank and recrystallize on the surface.

Rime formations, with their characteristic spiky white or comb-like appearance, often occur when the super-cooled water droplets of winter fog freeze on surfaces, coating those surfaces like a flocked Christmas tree.

Libbrecht’s fascination with snowflakes grew from interest in the physics of how crystals grow. Snowflakes were a convenient example of crystals.

During the phone interview, he offered one final bit of advice before signing off from his office in Southern California.

“Enjoy your weather,” he said. “Go out and look at some snowflakes.”

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