Abstract
The first two weeks of December 2021 were exceptionally active for severe convective storms across the central and eastern United States. While previous work has indicated this was related to the existence of a negative phase of the Pacific-North American pattern, we demonstrate that such a pattern was configured via dynamical linkages between multiple extratropical cyclogenesis events in the western North Pacific, the recurvature of Typhoon Nyatoh, and the subsequent phase evolution of the North Pacific jet. These processes were found to aid in the excitation of Rossby wave packets and the amplification of upper-level flow downstream over the Pacific, ultimately configuring synoptic scale weather regimes supportive of anomalous high frequency and intensity severe convective weather in the contiguous United States In addition, abnormally warm Gulf of Mexico sea surface temperatures, aided by a period of antecedent synoptic scale subsidence, played a critical role in enhancing convective instability in the the surface warm sector. This work underscores the importance of cataloging these events for purposes of examining (and potentially enhancing) predictability.
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Current affiliation*: Cooperative Institute for Severe and High-Impact Weather Research and Operations, The University of Oklahoma, Norman, OK and NOAA/NWS/Storm Prediction Center
