Recent and Future Trends of Cold Season Extratropical Cyclones over the Eastern United States

Extratropical cyclones are one of the most significant atmospheric phenomena that occur in the eastern United States, as these systems provide precipitation, temperature changes, and sometimes even extreme weather. Currently, there is a lack of understanding on how extratropical cyclones will change due to global climate change. In this study, model output from various reanalysis products and several coupled climate models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are used to assess the number of cold season extratropical cyclones and trends in their tracks east of the Rocky Mountains for the recent past and also under future climate change (RCP8.5). Extratropical cyclones are identified using a tracking algorithm modified from similar studies but applied especially for the Eastern US. Results from reanalysis products indicate that there is not definitive shift in the average track of cyclones. However, their frequency has changed across the Eastern US, with an overall increasing trend in the number of extratropical cyclones over the Eastern US. Regionally, this increase is manifested in the South Central US mostly with higher variability elsewhere. From the models, in examining the historical runs for bias detections compared to the reanalysis, we find that the models indicate an overall lower cyclone density across the US with mismatched trends in some regions. Finally, in the future, results indicate that the number of extratropical cyclones will remain steady if CO2 levels follow the RCP8.5 trajectory. Additionally, the average decadal cyclone tracks do not appear to have any significant decadal or multi-decadal trend. Based on regional trends and variables connected to extratropical cyclone characteristics, the models suggest a possible northward and westward shift of cyclones from the U.S. Southeast region. Linkages and implications of these trends with other large-scale climate modes and societal impacts will also be discussed.