An Examination of Sudden Stratospheric Warming Characteristics and Their Relationship to Cold-Air Outbreaks over the United States

In the Northern Hemisphere cool-season, surface temperature and pressure anomalies can be present up to 60 days following the central date of a Sudden Stratospheric Warming (SSW). Preliminary results show the spatial extent and timing of the greatest impacts are widely variable and dependent on several factors, including SSW-type (split or displacement), decade (before or after 2000), stratospheric preconditioning, stratospheric polar vortex location, and climate modes (e.g., SOI, PDO, PNA, QBO, etc.). The research presented considers the magnitude of the peak 10-hPa polar cap (75-90˚N area-weighted average) temperature anomaly, the magnitude of the zonal-mean zonal wind, and the duration of the wind reversal during SSW events on the timing of cold air outbreaks (CAO) over the contiguous United States. The United States is partitioned into seven areas defined by the National Centers for Environmental Information (NCEI) climate regions. For this study, a CAO is defined by a three-day period that begins on the first day when a regional temperature anomaly is ≤ -1.25 standard deviations from climatology in any 3-day period from SSW onset to 60-days after. The results show there is a large variability in the timing and magnitude of SSW-associated CAO based on SSW characteristics. These SSW-associated CAOs are compared to CAOs that occurred in non-SSW years as well as anomalous warm events. The analysis is presented in the context of our current understanding of the dynamics and impacts of weak vortex conditions on the tropospheric flow with an emphasis on impacts in the United States.