Blizzards across the eastern two-thirds of the United States have steadily increased in frequency over the last century. Due to accelerating changes to the climate, including rising ocean surface temperatures (which leads to more moisture in the air), reduction in Arctic sea ice (which can affect the jet stream), as well as natural variability, the increase in severe winter storms in the eastern U.S. is expected to continue.

Unlike hurricanes and earthquakes, there is no widely used scale or index for assessing the impact of snowstorms. In recent years, however, the meteorological community has made several successful attempts to establish a standard for measuring the impact of extreme snow events that can be used to compare snowstorms over time.

The Regional Snowfall Index, introduced in 2014, ranks a snowstorm impact on a scale of 1 to 5 using data on a storm’s area of snowfall, the amount of snowfall, and the population affected. The RSI has since been used to retroactively classify nearly 600 snowstorms that occurred between 1900 and 2013.

To determine the worst blizzards of all time, 24/7 Wall St. ranked snowstorms based on their Regional Snowfall Index values, published by the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. We included the 25 snowstorms designated as Category 5 since 1900. Data on duration, region, affected area, and affected population also came from the NOAA. 24/7 Wall St. combined data on affected area and population for Category 5 storms that spanned multiple regions, considering it one event. Storm names, as well as measures of snowfall in the affected areas, came from various news and media sources.

Click here to see the worst blizzards of all time.