Renalda Colovich, age 12, of La Grange, Il
How doss snow differ from hail?
Hail; and snow, rain and sleet, are forms of precipitation ‑. a big word meaning fall. The weathery precipitations are created from moisture in the atmosphere and they fall down from cloudy skies. There is always a certain amount of moisture in the atmosphere, even over the driest deserts. It is hidden there as vapor, which is an invisible gas. Whether this moisture becomes snow, rain, hail or sleet depends upon weather conditions such as temperature and air currents.
Before it can fall as precipitation, the vapor in the air must first condense into a liquid or a solid. And this condensation follows very strict rules. The basic rule is that warm air can hold more moisture than cool air. A cubic yard of air at, say., 86 Fahrenheit degrees may contain almost a glass of water in the form of vapor. If this air is cooled to 60 degrees, it can hold only half this amount of vapor.
A s warm, vapor‑laden air cools its surplus vapor condenses, usually into misty cloud droplets. It may form a frothy cloud or mystery making mist, which is really a lazy cloud sitting on the ground. If weather conditions are right, the tint droplets gel together in millions to form raindrops. Snow and hail form when the weather conditions are slightly different.
Hail tends to form in the wild conflicts of a tempest. A thunderhead, for example, is a raging war between currents of warm and cool, damp and dry air reaching perhaps seven miles above our heads. There is usually a strong current of warm air rising up from the ground. The precipitation forming in the cloud may have trouble falling down through this current.
As the raindrops fall in the warm, moist regions of the cloud they are whisked around and aloft into regions of icy cold..
The liquid raindrops become pellets of ice. . Again and again they are whisked from areas of warm; wet rain to areas of icy cold. They gather coat upon coat of wet rain which freeze into jackets of ice. The hailstones buildup in onion skin layers of hard and soft ice and at last become heavy enough to break through the barrier of rising warm air holding them aloft: And down pelts the hail,
Snow is created in gentler conditions. The air is below the freezing point of water and as its vapor condenses it becomes, not misty wet droplets, but` microscopic fragments of ice. For a while, the tiny crystals may float in the air, forming a blanket of pearly grey cloud between us and the sun: Then the crystals gel together to form feathery snowflakes fluttering down to the grounds
The microscope shows that each snowflake is a delicate, six sided doily design. It takes this form because of the shape of the tiny vapor crystals from which it is made. It looks white, because microscopic pockets of air are interwoven in the design, of microscopic vapor, crystals.