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A prolonged winter storm that combines heavy snowfall, strong winds of more than 56 km per hour, and very low temperature, all resulting in very low visibility. |
The United States National Weather Service’s winter weather advisory, watch, or warning system helps meteorologists determine whether atmospheric conditions should be classified as typical winter weather, a snowstorm, or a severe blizzard.
In order for meteorologists to classify a winter storm as a snowstorm, the air temperature high in the atmosphere and near the ground must be below 0°C (32°F). There also needs to be enough water vapor in the air to form snowflake crystals. While snowstorms do not typically last very long (less than a few hours), they can bring high snow accumulations, which can be hazardous.
For a snowstorm to be considered a blizzard, it must also meet specific, though more severe, conditions. To be categorized as a blizzard, the storm must last for at least three hours and produce a large amount of falling snow. Blizzards also have winds measuring over 56 kilometers (35 miles) per hour. These winds cause a large volume of snow to blow around in the air and near the ground, decreasing visibility. Meteorologists will declare blizzard conditions if the snow limits visibility to the point where it is difficult to see an object more than 0.4 kilometers (0.25 miles) away.
Credit: National Geographic Society
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