When there is no much snow that people and animals cannot tell the earth from the sky, it is known as a whiteout. In this disoriented state, humans and livestock can lose their way and freeze to death. Blizzards carry the risk of hypothermia, frost bite, suffocation, and being stranded. Sub-zero temperatures, arctic conditions, and 100 mph winds in mountainous regions pose additional threats.
Forces of Nature: ThinkQuest 2000 (Team #C003603)
http://library.thinkquest.org/C003603/english/snowstorms/whatsablizzard.shtml
A snowstorm is when snow falls from the sky as precipitation. A blizzard is the worst kind of snowstorm, in which strong winds blow snow into snowdrifts (huge piles) that can bury people and possessions. Its official definition is a tempestuous, frigid snow storm with blustery, piercing winds of 35 miles per hour or more and a windchill factor as low as -20º Fahrenheit. Transportation is difficult and dangerous during blizzards because air temperatures can be 10ºF or lower, with visibility less than 400-500 feet.