Identifying, Tracking, and Evaluating Mechanisms of North American Cold Air Outbreaks (CAOs) Using a Feature Tracking Approach

North American cold air outbreaks (CAOs) are large-scale temperature extremes that typically originate in the high latitudes and impact the midlatitudes in winter. As they transit southward, they can have significant socioeconomic consequences. CAOs from winter (DJF) 1979 to 2020 were identified in the fifth major global reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ERA5) using an automated feature tracking approach (TempestExtremesV2.1). This allowed for the systematic identification of a large number of cases without using predetermined, Eulerian regions. Another important advantage of this approach was the ability to compute a feature tracked thermodynamic energy budget in a nonfixed domain for every identified CAO event. As an example, the thermodynamic energy budget analysis was used to quantify important processes for the 18–23 January 1985 CAO. The dominant mechanisms of cooling and warming as well as lysis locations (i.e., eastern or western) were then used to generalize detected CAO events into subcategories. The associated statistics, spatial footprints, and composites of 500-hPa height, sea level pressure, and temperature and winds at 850 hPa were analyzed for three subcategories that contained the majority of events. This analysis revealed that CAO events that form and dissipate through different mechanisms occur in different regions, have different intensities, and are associated with different large-scale circulation patterns. Finally, the analysis of associated North Atlantic Oscillation (NAO) and Pacific–North American (PNA) teleconnection pattern revealed that the PNA is typically in a positive phase for eastern CAO events and in a negative phase for western events resulting primarily from horizontal advection, whereas the NAO did not have any significant relationship.