Abstract
Extratropical cyclones are the primary driver of sensible weather conditions across the midlatitudes of North America, often generating various types of precipitation, gusty nonconvective winds, and severe convective storms throughout portions of the annual cycle. Given ongoing modifications of the zonal atmospheric thermal gradient resulting from anthropogenic forcing, analyzing the historical characteristics of these systems presents an important research question. Using the North American Regional Reanalysis, boreal cool-season (October–April) extratropical cyclones for the period 1979–2019 were identified, tracked, and classified on the basis of their genesis location. In addition, bomb cyclones—extratropical cyclones that recorded a latitude-normalized pressure fall of 24 hPa in 24 h—were identified and stratified for additional analysis. Cyclone life span across the domain exhibits a log-linear relationship, with 99% of all cyclones tracked lasting less than 8 days. On average, ≈270 cyclones were tracked across the analysis domain per year, with an average of ≈18 yr−1 being classified as bomb cyclones. The average number of cyclones in the analysis domain has decreased in the last 20 years from 290 per year during 1979–99 to 250 per year during 2000–19. Decreasing trends in the frequency of cyclone track counts were noted across a majority of the analysis domain, with the most significant decreases found in Canada’s Northwest Territories, Colorado, and east of the Graah Mountain Range. No significant interannual or spatial trends were noted in the frequency of bomb cyclones.
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