The dynamics and predictability of US winter extremes—a multiscale case study of the 2021 U.S. cold air outbreak

Since 1980, the U.S. experienced 338 different billion-dollar weather and climate disasters, with greater than 25% (n = 96) of these occurring in the cold season of December–March. These events can have lasting societal and economic impacts that make diagnosing their likelihood of occurrence in the next week, season, or decade an important problem in the context of our changing climate. This analysis will focus on a case study of the predictability and dynamics of the 2021 US cold air outbreak (CAO) and provide a multiscale overview of the event on subseasonal-to-seasonal (S2S) timescales. The analysis of the dynamics focuses on the role of the stratospheric recovery from the January 2021 sudden stratospheric warming and a stratospheric Rossby wave reflection event in the context of the development of high amplitude flow in early February 2021. The second part considers the ability of S2S forecast models to resolve the predecessor events to this CAO. The predictability of this CAO and the role of the stratosphere in the development of CAO are considered by analyzing both high-top and low-top S2S forecast model from the S2S prediction Project Database.