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Scientist's Corner

Dear SNOWy colleagues,

I would like to introduce you to Arthur Judson, an expert scientist that has agreed to work with the SNOW project again this year. Our great appreciation is extended to him. He has agreed to respond to some snow related questions from SNOW participants during the duration of the project. Post your questions and watch for answers on the SNOW Conference Center.

Consulting with a scientist in this way is an exciting way to extend our knowledge and experience with snow, but I encourage you to not let this take the place of your own inquiry. Think about the questions you have. Are they questions you can investigate yourself for an answer? If they are, that is the best direction for you. Remember, you are a scientist, too! Save the questions of the greatest challenge, that you can't find the answer yourself for our expert. I look forward to hearing from you. Include a note in your email stating this is a question you are really stuck on and need expert help with.

Bill Lindquist

SNOW Questions with responses from Art Judson

Miscellaneous notes from Art Judson

Note: Jan 26, 1999- Do you know if any of the teachers are present when the samples are collected out doors? A little on site presence can go a long way. And about the color of the boards -- were all them painted with exterior gloss white to minimize radiation effects? If not, that alone could cause high readings because the short wave incoming radiation can penetrate 30 cm or so into snow, and it could melt a thin layer at the board/snow interface. I think if they pay attention to the texture of the snow not only on top but all the way to the bottom that will help them distinguish when they might have a situation where the sample is not representative. It's OK to discard a sample that has been so affected. They don't have to keep bad snow samples and make computations on them. So the first decision is: is the present snow layer worth sampling i.e. is it no more than 24h old, has it been affected by wind, melt, rain, freezing rain, etc or has someone walked on the board destroying the sample? If the answer to any of the above is yes, then they should throw that sample away. Bad data are worse than none at all. They may wonder how someone thousands of miles away knows when something is wrong with a post, but snow follows certain physical laws, and when a sample is suspect, it jumps right of the page.

Any sample with a water snow ratio above .11 should have an explanation stating that there was or was not any wind effect and or melt/freeze, or mixed precipitation etc.

Note: Jan 11, 1999- Remarks about surface features of the snow cover or what is happening to it would help. Something like "particles moving on snow surface above the board", "melt crust in sample", "wind crust in sample" "evidence of drifting" etc. Ratios used in density distributions should be free of either melt or wind effects, and they should be from snow with no pollution from sleet, freezing rain, or rain anywhere in the sample. This extra detail would improve data quality and reliability...My boss once told me that "it is impossible to write too much on an instrument chart,or in the remarks columns. Even the presence of a dust layer is important to know about as it increases radiation absorption and can alter the sample.

Note: Jan 14, 1999- Was that snow this morning just fluff? A density or water/snow ratio below .04 is called "wild snow". It flies up in the air when you stomp on it. You can blow it from a railing. It just goes poof! It flies up in the air with great ease. You can walk easily through large quantities of it. Congratulations on getting some "wild snow". It doesn't happen very often so enjoy.

Note: Jan 14, 1999- The water/snow ratio is something the kids ought to know about. You can compute roof loads with it. Just the other day a roof of a large business collapsed in Toledo, OH. If the kids knew enough about snow to compute roof loads it would save some lives. Reason enough to learn I think. The data have many applications and it doesn't just mean that the snow is wet or dry.

Dr. Judson"Snowbursts that frequented his father's logging camps on Tug Hill, New York, fascinated Art Judson. As a young marine, he chased snowstorms in California's San Bernadino mountains, than found deeper snows in the Rockies and Cascades. After obtaining a B.S. in Forestry from Oregon State University in 1960, he started chasing avalanches as a Forest Service snow ranger in Colorado. He later became a career avalanche forecaster and snow scientist with the Forest Service Avalanche Project. "Jud" as he is know to his friends, organized a special network to provide weather, snow, and avalanche data for avalanche forecasting and warning across the mountainous West. He founded Colorado's Avalanche Warning Program, developed an avalanche forecasting model, and worked to establish a warning service in Alaska. Currently, Jud lives in Steamboat Springs, Colorado (average annual snowfall 171 inches with 300-600 inches falling on the nearby mountains), where he continues to enjoy snow greatly."

excerpted from Mr. Judson's book, The Snow Booklet. See the Snow Booklet's website for further information

Why is snow white?

Snow's color is related to its opaqueness, transparence, and its ability to reflect sunlight. The color of an opaque object depends on the frequencies of light it reflects. And the color of a transparent object depends on the light that it transmits. Snow reflects most of the visible wavelengths and it also transmits most of the other colors. This special combination of processes gives snow its very white appearance. If snow absorbed some other wavelengths its color would change, and believe it or not this happens to light that penetrates some distance into the snow cover. Prove it by poking a hole into the snow on a clear day. Look into that opening, and what color do you students see? You might ask me about this in the future if you like.

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How do snowflakes form?

Snowflakes are agglomerations of snow crystals which form around tiny nuclei in the atmosphere when humidity is very high and temperatures are below freezing. When snow crystals fall through layers of air near the freezing point they sometimes collide with and stick to other crystals. These clumps of crystals may grow to considerable size -- up to three inches in diameter. The technical name for a snowflake is a polycrystal.

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Why are no two snowflakes the same?

This makes me ask you why do you ask such complex questions? These questions are hard to answer. For this particular one I will only say that the type and shape of snow crystals are determined by temperature and the degree of supersaturation (humidities above 100 percent) they experience. Growth rate also determines form as does the fact that crystals may decay while falling to earth if they become too warm or if they fall through dry air for too long. Other things such as vapor pressure is also a factor and this varies with the shape of the crystal and the type of curvature the crystal's arms may exhibit. The form maybe simple (stars) or astonishing complex (spatial dendrites), there could be needles, prisms, plates, columns, capped columns, twelve pointed stars, six pointed stars, stars with broken pieces, irregular particles, germ crystals, cups, or combinations of all of these. Some crystals might take hours to reach earth, while others might disappear while descending or become attached to other crystals with different forms. Consider also that each crystal is constantly changing size and shape. The more complex they are, the faster they change. All together there are too many combinations for one person to find two crystals that are exactly alike and exactly of the same size. Even if they appear very similar, if you put them under a microscope, you will see many other features which make each one unique. There may be pits of varying sizes on parts of the crystals. They may have round corners or they may be faceted. All of these things keep people from finding two exactly alike crystals.

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Art Judson
Steamboat Springs, CO
A very snowy place.

Questions and Answers About SNOW from the National Snow and Ice Data website

Last update: January 16, 1999