A Multiscale Analysis of Major Transition Season Northeast Snowstorms

Major transition season Northeast snowstorms have the potential to cause widespread socioeconomic disruption in the form of transportation delays, infrastructure damage, and widespread power outages. Because heavy, wet snow tends to occur in transition season Northeast snowstorms, lesser accumulations can result in greater disruption than if the same accumulation occurred in winter season Northeast snowstorms. Motivated by the opportunity to improve scientific understanding and operational forecasting of major transition season Northeast snowstorms, we are conducting a multiscale analysis of this class of snowstorms that focuses on documenting: 1) the planetary-to-synoptic-scale flow patterns occurring prior to and during major transition season Northeast snowstorms, with emphasis on the role of moisture transport occurring within atmospheric rivers in the formation and evolution of this class of snowstorms, and 2) the synoptic-to-mesoscale flow patterns in the extratropics occurring prior to and during major transition season Northeast snowstorms, with emphasis on the formation and maintenance of regions of lower-tropospheric cold air that coincide with areas of heavy snowfall.

An objectively developed list of major transition season Northeast snowstorms that occurred during fall and spring from 1983 through 2013 was constructed using National Centers for Environmental Information monthly Storm Data Publications. This list was used to construct composite analyses for categories based on characteristic patterns of lower-tropospheric cold air that coincide with areas of heavy snowfall and to perform illustrative case studies of the categories. The composite analyses and case studies will be used to document the planetary-to-mesoscale flow patterns occurring prior to and during major transition season Northeast snowstorms and to consider the hypothesis that atmospheric rivers play a key role in the formation and evolution of this class of snowstorms. We will address this hypothesis by applying an objective atmospheric river detection algorithm. We also will document moisture transport along parcel trajectories to diagnose moisture sources for areas of maximum snowfall, as well as to diagnose the evolution of selected thermodynamic quantities and moisture variables along the trajectories for selected case studies. While performing the composite analyses and case studies, we will diagnose the processes that contribute to the formation and maintenance of regions of lower-tropospheric cold air that coincide with areas of heavy snowfall.