Why do blizzards occur

While a large amount of snow must be present, the main factors in determining a blizzard from other snow events are wind speed and visibility. The snow can either be falling as precipitation, which are the most common blizzards, or be present on the ground, which are known as ground blizzards. In general, blizzards occur when a mass of warmer air collides with a mass of very cold air.

The cold air mass cuts under the warm air mass, and as the warm moist air rises upwards it forms snow. The collision of the air masses also provides the atmospheric tension required for high wind speeds. There are several ways in which these air mass collisions can occur. In the United States, warm air masses from the Gulf of Mexico can collide with cold air masses from the Pacific. These collisions result in blizzards over the plains.

In many storms in continental interiors, it is not uncommon for little new snow to be associated with a blizzard, due to a lack of moisture associated with Arctic and Antarctic air masses in winter. In such circumstances, blizzard conditions are largely the result of winds blowing the existing snow cover. However, blizzards in some regions for example, those in Western Europe and the Asian coast of the North Pacific, and "nor'easters" in the northeastern United States are characteristically accompanied by heavy snowfall.

Blizzards are produced by strong winds: katabatic winds and those generated by steep sea-level pressure gradients associated with storms in high and mid-latitudes latitudes during winter. A single storm can occur over large areas of a continent and a severe blizzard may persist for a week or more.

A blizzard that struck Saskatchewan, Canada, in lasted 10 days, burying a train in a snowdrift a kilometer long. The most severe blizzards occur in Antarctica, with winds exceeding Historically, high death tolls have been associated with the most severe blizzards. A spring blizzard, in the United States in , killed more than people, and died in a storm in In addition to the risks resulting from high wind chill values and exposure, blizzards generate other hazards. Whiteouts are often associated with blizzards, producing dangerous travel conditions.

The blowing snow, limited visibility, absence of shadows, and lack of contrast between objects can cause a loss of depth perception and conditions in which even nearby objects may be rendered invisible.

The persistent winds associated with blizzards may cause severe damage to buildings, and can block transportation links and bury struc tures in massive snowdrifts. The sun heats the ground and pushes masses of warm, moist air upward, creating unstable air columns.

As it rises, the moisture condenses to form clouds, which are jostled by internal turbulence. The "tricky part" for making thundersnow is creating that atmospheric instability in the wintertime.

For thundersnow to occur, the air layer closer to the ground has to be warmer than the layers above, but still cold enough to create snow.

During thundersnow events, heavy snowfall is to be expected. In some cases, two inches per hour is possible. What is sleet? Sleet is just rain drops that freeze into ice pellets before reaching the ground. Sleet usually bounces when hitting a surface and does not stick to objects. However, it can accumulate like snow and cause a hazard to motorists. What is freezing rain? Freezing rain is just rain that falls onto a surface with a temperature below freezing. This causes it to freeze to surfaces, such as trees, cars, and roads, forming a coating or glaze of ice.

Even small accumulations of ice can cause a significant hazard. What is an ice storm? An ice storm is a type of winter storm caused by freezing rain.

The U. National Weather Service defines an ice storm as a storm which results in the accumulation of at least 0. How do ice storms form? Ice storms form when a layer of warm air is between two layers of cold air. Frozen precipitation melts while falling into the warm air layer, and then proceeds to refreeze in the cold layer above the ground. This creates freezing rain or a glaze of ice. What is frost?