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The northeastern United States is vulnerable to many impacts from snowfall-producing winter cyclones that are amplified by the proximity of population centers to storm tracks. Historically, climatic snowfall assessments have centered around seasonal means even though local impacts typically occur at scales of hours to days. To detect snowstorms at the event level, an objective algorithm is defined based on the Regional Snowfall Index. The metric collocates storm snowfall with population to produce statistics of snowstorms with societal impacts. When applied to the Community Earth System Model Large Ensemble, broad declines in snowstorm frequency are projected by the later 21st century. These decreases are primarily due to a warmer atmosphere less conducive to snowfall as the predominant precipitation type. However, reductions are less significant for major events, since more hostile thermodynamic environments are partially offset by increased precipitation associated with cyclones that dynamically drive high-impact snowstorms.

Plain Language Summary Snowstorms that strike the northeastern United States result in risks to health and welfare, transportation disruption, lost spending productivity, structural damage, and power outages. This letter demonstrates an automated technique that finds and counts individual snowstorms in climate model data, eliminating the need to do so by hand. When this metric is applied to a large number of climate simulations, northeastern U.S. snowstorms are forecast to decrease in frequency over the coming century. However, this decrease is nonlinear across intensity, being larger for storms producing less snow over smaller areas than it is for major storms impacting populated areas with heavier snowfall. Warmer temperatures throughout the atmosphere result in precipitation less likely to fall in the form of snow in the future, but increases in cumulative precipitation associated with cyclones in the northeastern United States are projected. This means that while the likelihood of a given cyclone-producing snow (instead of rain) decreases, when atmospheric conditions are cold enough, storms drop more snowfall, therefore partially offsetting reductions in high-impact snowstorms moving forward.