Impacts of Sudden Stratospheric Warming on Extreme Cold Events in Early 2021: An Ensemble‐Based Sensitivity Analysis

Impacts of sudden stratospheric warming (SSW) on three severe cold events (C1–C3) over Northern Hemisphere in early 2021 were investigated using subseasonal-to-seasonal ensemble forecasts. The SSW was characterized by successive displacement and split the polar vortex (SPV). Ensemble-based sensitivity analyses showed that C1 Siberia C2 western Canada more related to SPV variations at a lead time 1–2 weeks than C3 central U.S. Within forecasts, elongated with higher geopotential height northern Eurasia conducive C1, whereas poleward retreat from contributed C2. forecast accuracy heights sensitive region 2 significantly correlated skill tropospheric circulation pattern preceding implying prediction specific weather may be improved better key features variations.