Winds must be sustained at 40 km/h or more for at least 4 hours combining with falling or blowing snow to cause visibilities to be reduced to 400 m or less. Hence the 4-4-4 rule. However, there is an exception: areas north of the treeline line in Canada have to have the same conditions but it must last at least six hours to be deemed a blizzard.
Our definition of a blizzard differs from that of our neighbours to the South.
In the U.S., to be a blizzard, a snow storm must have sustained winds or frequent gusts that are greater than or equal to 56 km/h (35 mph) with blowing or drifting snow which reduces visibility to 400 m or 0.25 mile or less and must last for a prolonged period of time—typically three hours or more.
It was the 1972 Iran Blizzard, which caused approximately 4,000 deaths. It dropped as much as 26 feet (7.9 m) of snow – that’s like a two and half story building worth of snowfall, and completely covered 200 villages. After a snowfall lasting nearly a week, an area the size of Wisconsin was entirely buried in snow.
According to Associated Press reports, some rescue workers who’d been dropped on a snow drift burying a village called Sheklab dug for two days straight, burrowing through 8 feet of snow, only to find 18 frozen bodies and no one—not one single person in a population of 100—still alive.
The second deadliest blizzard on record tore through Afghanistan in 2008, bringing -30 degree temperatures and killing an estimated 926 people.
Source(s): theweathernetwork | wikipedia | weirdfm