Understanding the Weather [ 429 



ful flakes, of lacelike design, usually form in warmer air currents, 

 close to the earth. 



SNOW AND SLEET 



"Aren't snowflakes frozen water?" your alert child may 

 wonder. "What makes them soft and white? Why aren't they little 

 pieces of ice like sleet?" 



Good questions, these. Snowflakes are frozen moisture, like ice, 

 but they are formed when the moisture in the air condenses 

 (changes from vapor to liquid form) at a point below freezing. 

 If, on the other hand, the moisture condenses into rain first and 

 then freezes, sleet results. The time when the freezing takes place 

 accounts for the difference. 



SNOW is MOSTLY AIR 



As the crystal particles of the snowflake take shape, many 

 tiny reflecting surfaces are formed with air spaces between them. 

 It is these air spaces that make snow soft and dazzling white as 

 it reflects the light of sun and moon. Also, it is odd but true that 

 the fluffy, new-fallen snow forms an effective blanket, protecting 

 whatever it covers from freezing. (Air is one of the best insulators 

 against heat and cold.) Newly fallen snow usually contains only 

 one part of ice to ten or twelve parts of air; and even an old snow 

 is at least half air. 



The popular theory that the temperature may be "too cold for 

 snow" is definitely wrong. The extreme dryness of very cold air 

 does make heavy snow unlikely, but even then a warm wind may 

 move into the upper atmosphere bringing moisture with it and 

 thus resulting in snowfall. 



Frost on the Windowpane 



The appearance of frost on windowpanes is nature's artistic 

 announcement of the arrival of winter. In many modern homes, 

 where storm windows are used, this lovely effect is not so common; 

 but sooner or later most children have an opportunity to see these 

 exquisite icy window decorations. It is pleasant to credit them to 



