Alaskan Ridge Blocking and Associated Winter Cold Conditions Over North America

ABSTRACT Atmospheric blocking over the northern North Pacific–Alaska sector has a central role in shaping winter weather variability and cold‐air outbreaks across central and eastern North America. Motivated by recent high‐impact Alaskan ridge events, this study examines the climatological characteristics of Alaskan atmospheric blocking and its downstream temperature response based on reanalysis data during January–February (JF) 1979–2023. The meridional gradient of potential vorticity (PVy) is used here as a physically motivated dynamical index in which a reduced PVy is associated with zonal wind reversal and weakened westerly winds and conditions favourable for ridge amplification. The PVy index exhibits spatial structures and temporal evolution similar to the traditional Tibaldi–Molteni blocking index. Negative‐PVy anomalies over the Bering Sea occur in most winters, typically persisting for several days to one week. Composites based on negative PVy show a robust atmospheric circulation pattern characterised by enhanced ridging over Alaska and a downstream trough over North America, accompanied by negative near‐surface temperature anomalies over the central and eastern United States and positive anomalies over Alaska and the Pacific Arctic. Although negative‐PVy conditions are common in winter, prolonged blocking episodes spanning much of a month are rare, consistent with the transient nature of blocking events. Selected winters (1979, 1986, 1988 and 2018) are illustrative case studies that demonstrate the range of circulation structures and surface‐temperature responses, embedded within a long‐term climatological relationship. These results highlight the important meteorological role of Alaskan blocking and identify PVy as a simple, physically interpretable diagnostic of background‐flow conditions associated with North American winter temperature variability.