The snow forms only if the air is below freezing--when it is, the water vapor is capable of turning to ice instead of rain. These tiny ice crystals stick together, forming snowflakes. Once these snowflakes have collected enough ice crystals to be heavy enough to fall, they slowly fall to the earth. Depending on the temperature of the air in which they travel in, the snow droplets might end up returning to the water state, in whichc case the outcome will be rain and not snow.
As the snowflake falls to the earth, it collects more and more water droplets that form in an intricate pattern. (See snowflake page)
Too Cold To Snow
When the temperature falls below zero degrees Fahrenheit (or -18 degrees Celsius) you will notice that snow rarely falls. However even in the coldest place on earth, Antarctica, snow will fall at temperatures way below zero. This is due to the fact that moisture is more of a factor than temperature. As the moist air rises into the atmosphere and cools (because of a drastic temperature change) the water droplets cling to the floating dust particles in the air. If the conditions are right and the temperature is low enough, the water freezes into its ice crystals, forming snowflakes. The colder it is and the more water there is, the easier and large the snowflakes form. Because of this, it just can't be "too cold" to snow--instead, it can be too dry to snow. In this case the snow crystals can form but no water will remain to construct larger flakes. The flakes that do form are too small and evaporate before they reach the ground.
In short, no matter how cold the cloud gets, if it is capable of finding water droplets, then it is capable of forming snow. For example, Buffalo, New York can pick up water from Lake Erie no matter how cold it is, which is why there is always an abundance of snow.
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Plenty of people have remarked how silent and peaceful it is when snow is falling. But few people realize that there is actually a scientific explanation for this phenomenon. It is a result of the snow's texture. Hard, flat surfaces reflect sound, but the soft, irregular surfaces of the snowflakes absorb, or dampen the sound. You may notice the same effect in a carpeted room, which is much quieter than room with a tiled or wood floor. Both the snow falling through the air and the snow on the ground absorb sound, resulting in the peaceful silence of snowfall.
