A blizzard is defined by its wind, not by how much snow falls
A foot of snow drifting down on a still day is just a snowstorm. A blizzard needs strong, sustained wind that whips snow into near-blindness for hours. In fact, no fresh snow need fall at all: a ground blizzard simply lifts what is already lying there and hurls it through the air.
Official thresholds vary by country. The US National Weather Service requires sustained winds or frequent gusts of at least 56 km/h, with blowing snow cutting visibility to 400 metres or less, for about three hours. Environment Canada sets the wind bar at 40 km/h but demands four hours, rising to six north of the Arctic tree line. A severe blizzard adds winds above 72 km/h and temperatures of minus 12 °C or colder. In Antarctica, winds pouring off the ice plateau average around 160 km/h.
The word probably imitates the sound of a violent gust, sharing roots with blow and bluster; it was first used for weather in 1829, meaning a violent blow, and spread through newspapers during the savage winter of 1880 to 1881. In North America, blizzards brew when the jet stream dips far south and frigid polar air collides with warm, moist air from the Gulf of Mexico. The treeless Great Plains are especially exposed, and in a true whiteout the horizon vanishes; people have become lost only three metres from their own front door.
That 1880 to 1881 winter began with an October storm that buried two-storey houses to their upper windows, stranding farmers with crops unharvested and fuel uncollected. A nine-day blizzard in February 1881 filled streets to the rooftops, forcing people to tunnel, and the spring thaw sent ice jams down the Missouri River that washed away much of Yankton. Laura Ingalls Wilder recounted it in her children's book The Long Winter, including trains halted until spring and near-starvation in her town.
Other storms were deadlier. The Great Blizzard of 1888 dropped up to 130 centimetres of snow on the American northeast and killed about 400 people, the majority of them New Yorkers. Iran's blizzard of 1972, the deadliest on record, reportedly killed 4,000 and buried some 200 villages under up to 7.9 metres of snow. The 1993 Storm of the Century reached from Canada toward Central America and cut power to more than 10 million US customers.
Source: Blizzard
