An Updated Climatology of Extratropical Cyclones Across the Central United States

Previous regional studies of extratropical cyclone characteristics and predictability focus predominantly on coastal North America due, in part, to their larger population densities. Yet, the Central U.S. is also a favorable region for lee cyclogenesis to the east of the Rocky Mountains. Consequently, this study focuses on identifying cyclone characteristics across the comparatively understudied Central U.S. This region’s distinctive location in the center of the continental United States and complex topography contributes to unique forecast challenges, including uncertainties in the prediction of storm intensity, cyclone location, and concomitant areas of heavy precipitation. The operating status of schools, restaurants, government offices, and airports are all affected by these forecasts, resulting in considerable societal and economic impacts. To begin investigating the characteristics of Central U.S. cyclones, this study performs a climatological analysis of cyclones that will provide a baseline for future analyses into cyclone predictability and the effects of climate change in this region.

Central U.S. cyclones were discerned within the ERA5 reanalysis between 1980–2021 using a cyclone identification method adopted from previously published work (Wernli and Schwierz 2006; Sprenger et al. 2017). This unique dataset facilitated an analysis of the monthly and seasonal frequency of Central U.S. cyclones, in which few significant trends were observed during the 42-year period of study. Self-Organizing Maps (SOMs) trained using mean sea-level pressure anomalies from ERA5 were subsequently used to examine the variability in large-scale weather regimes conducive to lee cyclogenesis across the Central U.S. The extent to which the characteristics of cyclone environments (i.e., frontal structure, moisture sources, upper-level jet stream structure, etc.) vary as a function of the prevailing weather regime were also investigated.

References:

Sprenger, M., Fragkoulidis, G., Binder, H., Croci-Maspoli, M., Graf, P., Grams, C. M., Knippertz, P., Madonna, E., Schemm, S., Škerlak, B., & Wernli, H. (2017). Global Climatologies of Eulerian and Lagrangian Flow Features based on ERA-Interim, Bulletin of the American Meteorological Society, 98(8), 1739-1748.

Wernli, H., & Schwierz, C. (2006). Surface Cyclones in the ERA-40 Dataset (1958–2001). Part I: Novel Identification Method and Global Climatology, Journal of the Atmospheric Sciences, 63(10), 2486-2507.