Years with heavy seasonal snow and extreme snowstorms continue to occur with great frequency as the climate has changed. The frequency of extreme snowstorms in the eastern two-thirds of the contiguous United States has increased over the past century. Approximately twice as many extreme U.S. snowstorms occurred in the latter half of the 20th century than the first.
The Science Behind Snowmaggedon
Conditions that influence the severity of eastern U.S. snowstorms include warmer-than-average ocean surface temperatures in the Atlantic. These can lead to exceptionally high amounts of moisture flowing into a storm and contribute to greater intensification of the storm. Unusually high ocean surface temperatures in the Atlantic were a contributing factor to the February 5–6, 2010, snowstorm dubbed “snowmaggedon” that hit Washington, DC, with 17.8 inches of snow at Reagan National Airport—the fourth highest total storm amount for the city at the time.
Natural variability can affect ocean surface temperatures, but as global surface temperatures increase, the temperature at any time is higher than it would have been without climate change. Overall, global ocean surface temperatures have increased at a rate of +0.18°F per decade since 1950.
Also, some recent research has shown that increasing surface temperatures and reductions in Arctic sea ice may produce atmospheric circulation patterns that are favorable for winter storm development in the eastern United States. Most notably, a greater prevalence of high pressure blocking patterns over the North Atlantic that result in cold outbreaks in the eastern United States along with slower moving systems can further exacerbate the persistence and severity of a storm.
Snow and El Niño: A Perfect Match
In addition, studies have shown that natural variability associated with the presence of El Niño conditions has a strong influence on the incidence of severe snowstorms in the eastern United States. Based on an analysis of the top 100 snowstorms in six regions east of the Rocky Mountains, scientists found that severe snowstorms are approximately twice as likely to occur in the Northeast and Southeast regions during years when a moderate to strong El Niño is present as compared to years when neutral conditions exist.
For now, it remains to be seen how factors such as ocean surface temperatures, the influence of El Niño, and conditions in the Arctic influenced the severity of the recent snowstorm that affected the Mid-Atlantic.