Often regarded as fun and magical to children and a headache to adults, snow has properties that make it unique with respect to other forms of precipitation such as rain, sleet and ice. Under certain circumstances, it can also be quite dangerous, especially when traveling by automobile or if heavy amounts fall. It also has a significant impact on our culture, particularly around the holiday season when it appears in television shows, movies and holiday songs. Snow's beauty, uniqueness, and hazard potential make it one of the most dynamic weather phenomena.
Facts about Snow
- Like all precipitation, snow forms in clouds. The temperature between the clouds and Earth often determines whether the precipitation arrives at the ground as snow or a different type of precipitation.
- Not all snowflakes are perfect symmetrical, hexagonal shapes. Many are round or lumps of crystals.
- Snow appears white to us because of the way its crystalline structure reflects and refracts light.
- An single inch of rain would create 10 - 13 inches of snow.
- Aomori City, Japan receives the most annual snowfall each year on average, with approximately 312 inches falling each year. Syracuse, Quebec and Buffalo also fall in the top 10 cities that receive this precipitation.
What causes snow to occur?
Snow is a product of the water cycle. In the water cycle, some of the water on the Earth in oceans, streams, lakes and rivers gets heated by the Sun and evaporates into water vapor. As the water vapor rises it cools and condenses, and as it does it begins to form clouds. In clouds, the air is colder because of their altitude higher above the Earth. Water vapor will collect around dust particles in the air and cool into water droplets or freeze into ice crystals. In order for snow to occur, the temperature in the clouds will have to be low enough for ice crystals to form.
As more and more water vapor begins to freeze around these new ice crystals, their weight eventually causes them to begin falling through the cloud toward the Earth. Not all of the crystals will make it to the ground. The ones that do are what is known as precipitation. How the ice crystals arrive will depend mostly on the temperature of the air between the cloud and the ground. If warm air occupies the space, the ice crystals will melt back into water droplets and fall as rain. If the air is colder, the crystals can fall as freezing rain, sleet or snow.
The air between the cloud and the ground must be right at or very close to 32 degrees Fahrenheit (0 degrees celcius) for snow to reach the ground. This is the freezing point of water. If the temperature at and near the ground is too much higher than this, the crystals will fall as a different type of precipitation.
What do snowflakes look like?
It is a common misconception that all snowflakes are perfect hexagonal shapes. While these certainly do occur, they are by far the exception rather than the rule. In reality snowflakes can be round, lumps of crystals, the striking hexagonal shape and other shapes as well.
Snow is somewhat unique to the other forms of precipitation in that it accumulates rapidly. In fact, a single inch of rain would make between 10 - 13 inches of snow! This is partly because water is one of very few elements that expands when it freezes. The greatest accumulation ever recorded over 24 hours occurred in a village in Italy named Capracotta.
For the most part, snow is stationary after it hits the Earth and accumulates. There are several exceptions to this. The first exception is an avalanche. Avalanches occur when snow accumulates at higher elevations on sloped surfaces, and then breaks free down the slope. Human activity, seismic activity and gravitational pull if too much snow accumulates, are all potential causes of avalanches.
Another exception is known as a ground blizzard. Ground blizzards are rather rare, but as blizzards are defined ONLY by wind speeds, visibility and duration, strong, high speed winds can pick up enough existing snow to cause one.
Safety precautions for non-blizzard snow events will greatly depend on where a person lives. In towns and cities that are located in areas which regularly or often receive snow, local governments are better equipped to respond after snow has fallen or started falling. This response often includes sending out plows to clear the roads, and also trucks that dump salt or sand on the roads to prevent them from icing. In these areas, safety precautions are mostly observed at the onset of a snow event. Roads can become slick or slippery even after small amounts have fallen, especially prior to plows arriving to clear them. Roads can still be hazardous later after the event, particularly if slush - a mixture of melted snow, salt, sand, dirt and rocks - refreezes overnight, and also on bridges or overpasses. In some instances, if the amount of snowfall predicted is sizeable enough, it may still be advisable to have some supplies on hand and a secondary place to go should the larger storm cause the power and heat to go out, or make transportation on roadways difficult.
Locales which do not regularly receive this type of precipitation are generally not quite as well equipped, as the cost to maintain the equipment is far too high for the limited use the equipment will see. A smaller snow event which would have caused little issue to the cities described above can incapacitate cities that lack plows and salt trucks, sometimes for several days or longer. In these areas, prior to a snow event, people will often buy enough food supplies to carry them through the event and any expected fallout, and some even have a secondary source of heat such as a wood burning fire place or generator. Road travel in these areas can become hazardous and remain that way for days, as packed snow that has been driven on turns to ice. Low temperatures can become an issue if there are power outages and emergency vehicles have difficulties moving from one area to another.
Snow in Film and Culture
- Snow is often seen in movies centered around the Christmas holiday. Examples of these include "A Christmas Story", "Elf" and "Home Alone".
- In some movies, it plays an integral part in the film, and may alter the course of the film, as in "Groundhog Day", and "Family Man".
- In Vince Guaraldi's classic musical score and "Skating", it is easy to imagine the music as snowflakes falling to the Earth.