Forest Preserve District of Cook County, Illinois
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Snow
Nature Bulletin No. 588   January 23, 1960
Forest Preserve District of Cook County 
Daniel Ryan, President
Roberts Mann, Conservation Editor
David H. Thompson, Senior Naturalist

SNOW
Snow is one of nature's most remarkable phenomena and of incalculable benefit to mankind. It brings fun and adventure, beauty and tranquillity, to young and old. Like anything else, there can be too much of it -- especially in metropolitan areas -- but, fundamentally, snow is good for the land and in the final analysis we all depend upon the land.

Farmers and gardeners dread a snowless period of bitter cold. They welcome snow because a thick porous blanket of it, having myriads of air spaces, is nature's best insulator for roots and bulbs in the ground. For example, one test revealed that when the air temperature at the surface of a deep snow was 27 below zero, the temperature of the soil at a depth of seven inches underground was 24 above zero -- an amazing difference of 51 degrees.

Snow protects crop plants -- such as wheat, rye, clover and alfalfa, which commonly live through the winter -- from "winterkill". Without snow during periods of alternate freezing and thawing, extreme changes cause the soil to swell and heave, perhaps several inches, breaking the plant roots and exposing them to the frigid air.

Farmers, gardeners, and also foresters welcome snow for another reason. N conserves and supplies water to soils in the ideal way. Rain falling on bare frozen ground is not absorbed and runs off rapidly into the watercourses and lakes. A blanket of snow melts slowly at the top and bottom. Most of it is absorbed by the soil or conserved in crevices, low spots, mats of dead vegetation, and the humus on forest floors.

In our western states there are vast areas where, because of scanty rainfall during the growing season, crops must be irrigated. They depend upon the water from rivers fed by tributaries and streams tumbling down from distant mountains where the deep snows melt during spring and early summer. Many cities, notably New York and Los Angeles, depend upon snow-fed reservoirs and rivers for their water supply.

Snow is a substance of phenomenal construction and beauty. Its crystals are frozen directly from invisible molecules of water vapor. When the vapor goes through a liquid stage it falls as lumps of sleet or as hail. The crystals are generally transparent but appear white because of the light reflected from their many brilliant facets. It is fascinating to examine, with a magnifying glass, snow flakes that fall upon your coat sleeve. When you touch or breathe upon them they dissolve into scattered fragments or droplets of mist.

If snow falls from very high cold clouds, its crystals will be assembled into either small, six-sided, needle-like columns or three-sided plates. Then we describe the snow as "dry and powdery". The large flakes that float down from warmer low clouds, especially when there is no wind, are most interesting. Then the crystals gravitate into flat "wheels", perhaps a half inch in diameter. The basic form of a wheel may be that of a six-pointed star, or a hexagonal plate with six identical patterns, or a combination of the two.

Unseen in the center of such a flake, is a tiny grain of dust, or a dot of snow from a high cold cloud, that served as the nucleus upon which the vapor crystals swarmed and stitched a lacy doily in the sky. Each flake is a masterpiece of delicate design, and no two of them are alike.

Your pupils will discover a fairyland of beauty in snowflakes beneath a magnifying glass.


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