Snowstorms
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.
The most famous recorded blizzard is the Great Blizzard of 1888, which occurred between March 11 and 14. This blizzard extended all the way from the American states of Maine to Maryland. About 139 centimeters (55 inches) of snow brought newly growing cities in New England and New York City, New York, to a screeching halt. During this time, about one in four people living in the United States lived in one of the New England states, which made the blizzard all the more devastating. About 400 people died during this storm.
A more recent example of catastrophic blizzards would be when two 2010 blizzards formed back-to-back in the Washington, D.C., area on February 4–7 and February 9–11. The first storm brought snow to Pennsylvania and extended through North Carolina. The total amount of snow from this first storm varied from 25 to 76 centimeters (10 to 30 inches). The storm impacted over 45 million people in the northeastern part of the United States. Then, before the states could completely dig out from the storm, a second blizzard hit. The Washington, D.C., area reported snowfall totals of 15–38 centimeters (6–15 inches) from the new storm, and nearby Maryland reported over 60 centimeters (24 inches) on top of the snow that was already on the ground.