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A Snow Blizzard Defined

written by: Terrie Schultz•edited by: Donna Cosmato•updated: 5/15/2011

A blizzard is a particularly hazardous type of winter storm. Learn about the conditions that a storm must meet to be classified as a blizzard, and what to do if you are caught this type of storm.

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    How a Blizzard Differs from a Severe Winter Storm

    What is a blizzard? According to the National Weather Service, in order for a severe winter storm to be classified as a blizzard, three conditions must be met: wind speed, visibility, and duration.

    A blizzard is a winter storm with winds reaching speeds of 35 or more miles per hour either as sustained wind or frequent gusts, visibility of less than 1/4 mile (400 meters), and a duration of at least three hours. Severe blizzards have wind speeds of greater than 45 miles per hour, temperatures of 10 degrees Fahrenheit (-12 degrees C) or below, and almost zero visibility. Most blizzards are storms with currently falling snow, but low visibility can also be caused by blowing snow picked up by the high winds, a condition known as a ground blizzard.

    Blizzards occur when a cold arctic air mass moves south into the temperate zone and meets a warmer air mass. The boundary where two air masses of different temperatures and pressures meet is called a front. Severe weather often occurs at fronts.

    The wind chill factor due to the high winds creates an effective temperature that feels far lower than the actual temperature. For example, if the actual temperature is 0 degrees Fahrenheit, and the wind is blowing at a speed of 35 miles per hour, the effective temperature is 49 degrees below zero.

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    Blizzard Safety Tips

    The National Weather Service will issue an advisory Blizzard Warning when blizzard conditions are predicted. Blizzards are very hazardous because the strong winds and blowing snow create whiteout conditions, often making roads impassable. If blizzard conditions are predicted, it is recommended to avoid traveling until the severe storm has passed.

    While waiting out a blizzard indoors, make sure heating devices such as space heaters or fireplaces are being used safely. If there is no heat source, dress warmly in layers and insulate by covering windows and blocking drafts with towels or blankets.

    When driving in winter weather, always carry a survival kit in your car that contains water, non-perishable food, a knife, matches, a warm blanket or sleeping bag, flashlight and fresh batteries, ice scraper, change of clothes, first aid kit, shovel and tool kit. Always keep your gas tank full when driving in hazardous weather. If you are stranded while driving in a blizzard, here are some safety tips to follow:

    • Stay inside the vehicle; it is very easy to become lost in the blowing snow.
    • Run the car engine for ten minutes every hour to keep warm.
    • Open the window slightly to let in fresh air.
    • Ensure that snow is not blocking the tail pipe.
    • To make the vehicle more easily seen, tie a colorful scarf to the antenna. If it is after dark, turn on the interior light or headlights while the engine is running.

    It is important to minimize exposure to the extremely cold conditions during a blizzard in order to avoid hypothermia and frostbite. Hypothermia, a potentially fatal condition, occurs when the core body temperature drops even a few degrees below normal. Symptoms include shivering, confusion and loss of coordination. It is especially critical to protect children and the elderly from hypothermia.

    The definition of a blizzard is a severe winter storm that creates very hazardous conditions. Individuals that live in areas where blizzards occur should keep a close watch on the weather reports so they can take safety precautions if a blizzard is predicted.

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