Much of the United States has been under seige the past few weeks from winter blitzes and blasts from the arctic north.

   A winter storm warning is issued when hazardous winter weather is occurring, or imminent. This warning is used for winter weather conditions which may be a threat to life and property. A winter storm warning is usually issued for heavy snow accumulation approaching or exceeding six inches, ice accumulations, dangerously low wind chills, or a combination of the three. Warnings can be issued for lesser amounts of snow, say 3 to 6 inches, if the snow occurs with strong winds in excess of 20 miles an hour and/or significant sleet or heavy ice accumulations from freezing rain. Expected snow accumulation during a winter storm warning is four inches or more in 12 hours or six inches or more in 24 hours at low, flat areas such as the Plains or South. For mountainous areas less than or equal to 7,000 feet, a snowfall of six inches or more in 12 hours or 10 inches or more in 24 hours would prompt a warning. For elevations greater than 7,000 feet, snowfall of eight inches or more in 12 hours or 12 inches or more in 24 hours would qualify for a warning.

   Officially, the National Weather Service definition of a blizzard is, "great amounts of falling and/or blowing snow accompanied by winds in excess of 35 mph resulting in less than 1/4 of a mile of visibility for a period of time lasting more than 3 hours". From fall through the winter and well into spring, extratropical storms dominate the weather across much of the United States and other parts of the globe outside the tropics. "Extratropical" means the storms originate outside the tropics. These storms move generally west to east across the oceans and continents. Snowwstorms have historically plagued many states, notoriously those located in the Northeast and Midwest. Winter storms occur all over the country, but the "Snowbelt," stretching across the mid west and the Great Lakes to Maine and New England, receives the brunt of winter storms. Cities such as Buffalo, New York City, Milwaukee and Detroit experience snow falls that strand residents in the white stuff deep enough at times that the measurements are in feet rather than inches.

   German immigrants settling in Iowa witnessing this phenomena for the first time, coined the word blizzard, which comes from 'blitzartig', meaning 'lightning-like'. Early settlers and pioneers from Europe were astounded by the harshness and severity of the winters in the New World. Although accustomed to snow in their homelands, the confrontation of the blustery winter characteristics of the American snowbelt regions of brutal snowstorms, driving winds and freezing temperatures, was an unknown hardship for the newcomers.

  Marcia Politovich of the National Center for Atmospheric Research describes exactly how snow chrystals,the basis for the piles of snow that form in a blizzard, are formed. "As snow crystals form they take on a six-sided, or hexagonal shape, but with what seems like an infinite number of variations of being six sided. The temperature at which a crystal forms, and to less extent the humidity of the air, determine the basic shape. The many things that happen to snow crystals as they fall, such as collisions, partial melting and colliding with water drops that freeze to them, create even more shapes. This is why irregular crystals with no easily identifiable form are the most common. Some times crystals are a combination of more than one form. For example, hollow columns that form in air colder than -8 fahrenheit could grow thin plates on one or both ends as they fall through warmer air. While most people refer to shapes like those in the graphic above as snowflakes, flakes are really made of many snow crystals that have stuck together.

   Snow crystals form hexagonal shapes because of the way the two hydrogen atoms that join with an oxygen atom to form a water molecule attach to the hydrogen atoms of other water molecules."

   What are some of the results of these tiny beatiful flakes accumulating into piles and piles? Heavy snow can immobilize a region and paralyze a city, stranding commuters, stopping the flow of supplies, and disrupting emergency and medical services. Accumulations of snow can collapse buildings and knock down trees and power lines. In rural areas, homes and farms may be isolated for days, and unprotected livestock may be lost. In the mountains, heavy snow can lead to avalanches. The cost of snow removal, repairing damages, and loss of business can have large economic impacts on cities and towns.