Tornadoes, hurricanes, earthquakes...they all have scales that measure their intensity. And determining how intense they are is somewhat simple – the intensity is highest around a central point, such as an eye or epicenter, and diminishes as it radiates from the “origin.” But what about winter snow storms? After storms, like the Groundhog Day blizzard of 2011, it is natural to reflect back on what were the worst snow storms in memory. Characterizing their intensity, though, can be difficult - they are often amorphous in shape, extremely large in area, and have tremendous spatial variability in their intensity.
Scientists at NOAA have developed a system for ranking these storms that relies less on a single variable, but a rather complex calculation of several storm characteristics. The Northeast Snowfall Impact Scale ranks the social, economic, and transportation impacts of winter storms, factoring in how large the storm was, how much snow fell, and what populations were affected. Using a Category 1-5 ranking, the top Northeast U.S. storms are shown in this image. The darkest blue areas represent the most impacted areas of a storm system. Interestingly, as large and intense as the recent winter 2010-2011 storms have been, none (preliminarily) have made it into the Top 10 storms list. In fact, the Groundhog Day storm is currently ranked at #19. To have a significant statistical weight, a storm must produce 20-30" of snow and occur over highly populated areas. Since the Midwest is not as densely populated as the DC through Boston corridor, storms that peak in the Northeast will typically have a higher intensity on the NESIS Scale. The Groundhog Day 2011 storm, though severe in many places, did not have a wide-scale impact (e.g., 30 inches of snow) on major cities, and thus does not rank up with the storms of 1993, 1996, 1960, 2003, and 1961.