Winter storm

A winter storm is a meteorological event that occurs at colder temperatures and produces frozen precipitation. This precipitation may fall as snow, sleet, freezing rain, or a combination of the three. Winter storms can form only under specific meteorological conditions that require moist air, cold air, and lift in the atmosphere. Despite its name, a winter storm can develop in other seasons as long as the precipitation it produces is frozen. The United States has been hit with a number of devastating winter storms in its history. The most severe events dropped crippling amounts of snow and ice on parts of the country and resulted in numerous deaths and billions of dollars in damages.

Background

Winter storms develop when a mass of cold air interacts with warmer, moist air. This can occur along the boundary between the two air masses—called a front—or when air travels upward along a mountainside or passes over a warmer body of water. Since cold air is heavier and denser than warm air, an advancing mass of cold air will push away a mass of warm air, thereby displacing it and causing it to rise. This is known as a cold front. A warm front forms when advancing warm air encounters cold air and flows up and over the top of the cold air. If the rising air has sufficient moisture, it will condense as it rises and form clouds and precipitation.

Most storms develop around low pressure systems, an area where air pressure is lower than the air pressure surrounding it. Moving air, or wind, always travels from higher pressure to lower pressure. Because of the rotation of Earth, air in the Northern Hemisphere moves around a low pressure system in a counterclockwise manner. When atmospheric conditions are right, a low pressure system can pull down cold air from the north along its western edge. At the same time, warm, moist air flows up from the south on the eastern side of the low. The combination of the right amount of moisture and sufficiently cold temperatures can result in a winter storm.

In some cases, winter storms can form without the benefit of a low pressure system. When warm, moist air encounters a steep mountain, it is rapidly pushed up the mountainside. The rising air condenses and can form snow when it reacts with the colder temperatures at the mountaintop. For this reason, mountains, including those in warm regions such as Hawaii or the American Southwest, are often snow-capped. In areas such as the Great Lakes region of the United States, cold air flowing over the relatively warm surface of a large lake can accumulate a great amount of moisture. When this air reaches land, it can deposit the moisture as snow. Known as lake-effect snow, this phenomenon can often dump large amounts of snow in a short time.

Overview

Just as a winter storm's formation depends on specific meteorological conditions, the type of precipitation created depends on a number of factors. Snow forms when the temperature in the upper atmosphere is cold enough that moisture in the clouds freezes directly into ice crystals. If the temperature throughout the atmosphere all the way to the ground is below the freezing point of 32 degrees Fahrenheit, the precipitation will fall as snow. Snowfall may vary in intensity from flurries—light snow that falls for a brief period with little accumulation—to a blizzard—significant snowfall accompanied by high winds and reduced visibility.

Sleet is essentially frozen raindrops that form when ice crystals in the upper atmosphere encounter a thin layer of warmer air on the way down. If the cold air near the ground is thick enough, the crystals will briefly melt and refreeze before reaching the ground. If the ice crystals pass through a larger layer of warmer air and the cold air near the ground is thinner, then the crystals do not have time to refreeze on the way down. When these supercooled droplets hit the ground, they freeze upon impact. This precipitation, known as freezing rain, can form a potentially dangerous coating of ice on roads, power lines, and trees.

When winter weather is forecast for an area, the National Weather Service (NWS) has a system of alerts to notify the public about the severity of a storm. The NWS issues a "winter storm advisory" if the forecast calls for lighter amounts of precipitation that may cause slick conditions. A "winter storm watch" is issued when NWS confidence is medium that a storm can produce heavy snow, sleet, or freezing rain. A "winter storm warning" means NWS confidence is high that a storm will produce heavy snow, sleet, or freezing rain. The amount of precipitation needed to trigger a watch or warning varies by location. The NWS may issue winter storm alerts in northern regions for forecasts of 4 to 7 inches of snow or more. In southern areas, the alerts may be issued for smaller amounts.

According to records from the National Oceanic and Atmospheric Administration (NOAA), the largest single-day snowfall in the United States was 78 inches and occurred in Alaska. In the lower forty-eight states, Colorado posted a single-day record of 75.8 inches. Florida had the smallest record total, with 4 inches. The deadliest winter storm on record struck the northeastern United States in March 1888, dumping between 40 and 50 inches of snow on parts of Massachusetts, New York, New Jersey, and Connecticut. Dubbed the Great Blizzard of 1888, the storm created huge snowdrifts that buried houses and resulted in the deaths of more than four hundred people. In March 1993, the East Coast of the United States was hit by a large weather system that became known as the "Storm of the Century." The storm produced snowfalls of 2 feet or more in many areas and brought freezing temperatures and hurricane-force winds to southern regions. Twenty-six states were affected by the storm, which caused more than $6 billion in damages and killed almost three hundred people. "Snowmageddon" occurred in February 2010 when a blizzard followed by another blizzard hit the Northeast and Mid-Atlantic United States. Nearly 3 feet of snow fell on top of snow that had fallen from previous storms. Buildings collapsed, and forty-one people died.

The largest ice accumulation in US history occurred in 1961 when a freezing rainstorm coated north-central Idaho with 8 inches of ice. In January 1998, New England and Southern Canada were struck with a severe storm that left the region under almost 3 inches of ice. The storm destroyed millions of trees and downed power lines across the region, resulting in outages that lasted from days to weeks. The storm killed forty-four people in the United States and Canada and caused more than $4 billion in damages.

Bibliography

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Fleisher, Paul. Lightning, Hurricanes, and Blizzards: The Science of Storms. Lerner, 2011.

Grabianowski, Ed. "10 Biggest Snowstorms of All Time." How Stuff Works, 23 Feb. 2022, science.howstuffworks.com/nature/climate-weather/storms/10-biggest-snowstorms.htm. Accessed 7 Nov. 2024.

"Severe Weather 101." National Severe Storms Laboratory, www.nssl.noaa.gov/education/svrwx101/winter/types/. Accessed 7 Nov. 2024.