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Posted at 11:00 AM ET, 12/10/2008

The Science and Wonder of Snowflakes

By Ann Posegate

Wx and the City

* Mild Showers, Then Cold Rain: Full Forecast | Weather Wall *


Courtesy UCAR

With the D.C. area's first dusting of snow this past weekend and the slight possibility of more flakes this week, I got to thinking: What's so great about the white stuff?

Is it the magical twinkling of white crystals blanketing the ground? The opportunity for winter sports and outdoor play? The justification of cold temperatures, leafless trees and gray skies of winter, and the excuse to stay inside? The fact that no footstep is left untraced? Or the opportunity to see snowflakes, a manifestation of art and symmetry in nature?

I choose all of the above, with an emphasis on snowflakes. The science of snowflakes is one of the most amazing aspects about snowfall.

Keep reading for more on the science and wonder of snowflakes...

In order for snowflakes to form, atmospheric conditions must be just right; precipitation in a winter storm can change quickly and is very affected by temperature, humidity and wind. A snowflake is formed when a supercooled water droplet freezes onto a dust particle or other cloud nucleus, becoming an ice crystal. More and more ice crystals join on, forming a snowflake. Eventually, the aggregation is too heavy and falls several thousand feet to the ground. If the snowflake is fortunate enough to remain at or below freezing all the way to Earth's surface, it remains a snowflake (rather than turning into another type of wintry precipitation such as sleet).

Different temperatures and humidity levels along a snowflake's journey to the ground influence the shape it takes. Drier, colder snowflakes will often form feather-like dendrites (my favorite), whereas warmer flakes with more moisture content will form other plates or columns. Many snowflakes take on a hexagonal shape due to the lattice structure formed when water molecules join together. Furthermore, snowflakes that coalesce can form bigger, fluffier or asymmetrical shapes.

The first person to successfully photograph snowflakes was Wilson "Snowflake" Bentley, a farmer from Vermont who gained a fascination with the white stuff in the late 1800s. You can check out his photo gallery here. Other images of snowflakes worth looking at are the USDA Electron Microscopy Unit Snow Page and SnowCrystals.com.

The best part about all of this? You can easily learn to identify snowflakes yourself by catching them on a (cold) piece of black construction paper, checking them out with a magnifying glass, and finding their match using this printer-friendly guide.

Let's cross our fingers for some more snowflakes soon.

By Ann Posegate  | December 10, 2008; 11:00 AM ET
Categories:  Education, Posegate, Science, Wx and the City  
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Comments

I share your love of snowflakes, even if I'm not quite as enthused as some here by thoughts of large quantities of the white stuff. One tidbit for snowflake-lovers - Ann has linked several printable pages from the CalTech site, but if you go to the main page of that site (just type snowcrystals.com in your browser - address is actually more complex), there are photos and all sorts of good stuff to go with the two charts.

I also cut snowflakes, and that's another area generously served on the web. Maybe I'll try to cut some based on the real thing, instead of just wielding my scissors randomly!

Posted by: fsd50 | December 10, 2008 12:02 PM | Report abuse

fsd50 - Thanks for catching that error. I meant to provide the link to the main website. It's now fixed above, or click here.

Also, please feel free to share your advice for cutting the perfect paper flake...I can never seem to get it right. SnowCrystals.com also has a great page on their website ("Activities for Kids") that includes instructions for making accurate snowflake cutouts.

Posted by: Ann-CapitalWeatherGang | December 10, 2008 2:04 PM | Report abuse

I've always been fascinated by the seemingly infinite sizes and shapes of snowflakes. In fact it has been said that no two snow flakes are ever exactly the same (kind of like finger prints). And, I've been capturing snowflakes just to look at with a magnifying glass since I was a kid

As you mention, Ann, a snowflake has several thousand feet to fall once it becomes heavy enough to do so.A quick back of the envelope calculation shows that it can take over two hours for the flake to reach the ground and can land 50 miles or more from where it originated. I recall situations where it was snowing heavily under bright sun with the generating clouds far off in the distance.

Another thing to keep in mind given the above is that what one sees as snow on a radar display is not necessarily where the snow is reaching the ground

Posted by: SteveT-CapitalWeatherGang | December 10, 2008 8:13 PM | Report abuse

Kenneth Libbrecht also has several beautiful books out that discuss the science of snowflake. More importantly, they contain gorgeous, large-scale photos of snowflakes.

Posted by: dinergirl | December 10, 2008 10:57 PM | Report abuse

Dinergirl, Libbrecht's photos are indeed gorgeous - the CalTech site is basically his snowflake site.

Paper snowflake enthusiasts may want to look here:
http://www3.ns.sympatico.ca/dstredulinsky/home.html
for more info and links. This is the most exciting page I've found for this activity.

From my own experience, the secrets to great cut-paper designs are first, to have thin, tightly-bonded (not fibrous) paper (tracing paper, onionskin, and baking parchment are the best I've found, but some cheap notepads are surprisingly good).
Second, it MUST be folded accurately and creased sharply - make yourself a 30 degree template if necessary. Also, a Z or W fold (rather than folding always in the same direction, will give more accurate folds because of the lesser discrepancy between outside and inside layers.
Third, scissors must be sharp and you need to cut with the tips, not way down the blade. Most hobby cutters that I know use nail scissors or suture scissors, straight or curved as needed.

Happy snipping!

Posted by: fsd50 | December 11, 2008 10:11 AM | Report abuse

Quick note - I just discovered a stereo/3D image gallery of snow crystals on the USDA EMU site I mentioned above. It might take you a minute to see them in 3D the first time you try, but it's amazing after your eyes catch on!

Posted by: Ann-CapitalWeatherGang | December 11, 2008 10:19 AM | Report abuse

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