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Concept
Winter storm
Summary
A winter storm is an event in which wind coincides with varieties of precipitation that only occur at freezing temperatures, such as snow, mixed snow and rain, or freezing rain. In temperate continental climates, these storms are not necessarily restricted to the winter season, but may occur in the late autumn and early spring as well. A snowstorm with strong winds and other conditions meeting certain criteria is called a blizzard.
Winter storms are formed when moist air rises up into the atmosphere, creating low pressure near the ground and clouds up in the air. The air can also be pushed upwards by hills or large mountains. The upward motion is called lift. The moisture is collected by the wind from large bodies of water, such as a big lake or the ocean. If temperature is below freezing, , near the ground and up in the clouds, precipitation will fall as snow, ice, rain and snow mixed (sleet), ice pellets or even graupel (soft hail). Since cold air can not hold as much moisture as warm air, the total precipitation will be less than at higher temperature.
Winter storm warnings will be issued if:
Snow accumulation is or more in 12 hours, or or more in 24 hours.
Blowing snow is reducing visibility in large areas at winds less than .
Ice accumulations on surfaces are or more.
Ice pellets larger than are formed.
Wind chill index is less than for more than 3 hours and sustained wind speed of at least .
Snowstorms with wind speed of more than and reduced visibility of less than for 3 hours or longer are called blizzards.
Severe winter weather conditions called "winter storms", can be local weather fulfilling the criteria for 24 hours, or large storm systems covering part of a continent for several days. With large, massive winter storms, weather in any part of the area covered by the extreme weather is usually called "storm"; even if meteorological criteria for winter storms are not met everywhere. An example of this is the February 13–17, 2021 North American winter storm with snowfall and below freezing temperatures as far south as Texas and the Gulf of Mexico.
Official source
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