Blizzard has been very fascinating and dramatic phenomenon depicted in many animation films and children stories.For farmers and adults it is a nightmare and dreaded thing.It has potential to adversely affect a larger population over a vast geographical area.Many writers has depicted it very dramatically in literature.
“Snow blew down the Royal Gorge in a horizontal blur. With Ollie’s sleeping head in her lap and a down comforter around them both, she tried now and then to get a look at that celebrated scenic wonder, but the gorge was only snow-streaked rock indistinguishable from any other rock, all its height and grandeur and pictorial organization obliterated in the storm.” From Angle of Repose, Wallace Stegner
What is blizard ?
Blizzards are severe winter storms characterized by heavy snow and strong winds. When high winds stir up snow that has already fallen, it is known as a ground blizzard. Blizzards can impact local economic activities, especially in regions where snowfall is rare.There are three essential element for blizzard:-
History of devastation by blizzard
The Great Blizzard of 1888 affected the United States, when many tons of wheat crops were destroyed, and in Asia, 2008 Afghanistan blizzard and the 1972 Iran blizzard were also significant events.
The 1993 Superstorm originated in the Gulf of Mexico and traveled north, causing damage in 26 states as well as Canada and leading to more than 300 deaths.
Although it is not a man made disaster,however human activities like clearing of large patch of forest and making of very vast tract of agricultural field can contribute in formation of blizzard.
What is Ground blizzard ?
Ground blizzard refers to a weather condition where loose snow or ice on the ground is lifted and blown by strong winds. This can occur in the absence of precipitation, and can even occur when the sky is clear.
This is in contrast to “ordinary” blizzards, which are accompanied by heavy falling snow.
They can be especially dangerous as they occur after a winter storm has passed, when it is assumed that all forms of severe winter weather has ended.
When a blizzard is called ground blizzard ?
While the term “ground blizzard” is often associated with intense blowing and drifting snow conditions, there are specific criteria which must be met. Often such criteria will be determined by a country’s governing weather agency or other similar body.
US criteria for defining a ground blizzard
In the U.S, according to the National Weather Service a blizzard is defined as having sustained winds or frequent gusts of 35 mph or more, visibility frequently below 1/4 mile in considerable snow and/or blowing snow, and the above conditions are expected to prevail for 3 hours or longer.
Criteria for defining a ground blizzard in Canada
Environment Canada similarly maintains that widespread reduction of visibility to less than 400 meters due to snow and/or blowing snow and sustained wind speeds or gusts of 40 km/h or more must be present for at least 4 hours (6 hours for the Northwest Territories and Nunavut).
Role of topography in blizzard formation
Ground blizzards occur throughout the world, however unlike other winter storms, topography either aids in their formation or prevention.
The most important topographic element in a blizzard is the requirement for a vast amount of large open and relatively flat land.
Any type of flora, especially coniferous forms, will catch any drifting snow significantly reducing the blizzards effects. Any big obstruction in flow of blizzard wind diminishes the power of blizzard.
Role of temperature on blizzard formation
The temperature also plays important role .It must be below freezing point.The environment must also support temperatures cold enough to prevent any snow on the ground from melting and bonding the ice crystals together.
Types of ground blizzard
There are 3 different forms of ground blizzards:
- In horizontal advection conditions, the winds blow across the surface of the earth with very little if any large-scale upward motion.
- In vertical advection conditions, the winds exhibit large-scale upward motion lifting the snow into the atmosphere creating drifting waves of snow up to 500 meters in height.
- In thermal-mechanical mixing conditions, massive convective rolls form in the atmosphere and the blizzard may be observed from space with the blizzards convective rolls creating waves of snow (also known as snow billows) resembling lake or ocean effect snow bands. The extreme conditions can quickly bury a two story home and make breathing very difficult if not impossible if caught outdoors.
Where ground blizzards occur ?
Ground blizzards are common in the American great plains in the wake of snowstorms producing light, dry snowfall that is more easily picked up by strong winds.
They are also common in the Canadian Prairies, Siberia, Northern China, and also Arctic and Antarctic regions during seasonal transition periods, such as the spring and fall.