The Western Pacific (WP) pattern is a crucial driver of mid-latitude teleconnections in the Northern Hemisphere, strongly influencing East Asian winter temperatures. Although its seasonal impacts are well established, its subseasonal variability and long-term changes remain less understood. This study identifies significant changes in the influence of WP on surface temperature over South Korea since the mid-1990s using observational and reanalysis datasets. Our analysis reveals a significant shift in the WP teleconnection, with its influence strengthening in December but weakening in January and February. This change is attributed to an anomalous displacement of the WP-associated anticyclone and modulated by interactions with the Arctic Oscillation. Furthermore, seasonal forecast models from the Asia–Pacific Economic Cooperation Climate Center multi-model ensemble capture the WP-induced temperature variations in December; however, strong modulation by El Niño–Southern Oscillation inhibits the independent effect of the WP teleconnection. These findings highlight the critical gaps in seasonal forecast models and emphasize the need for improved representations of WP teleconnections in subseasonal forecasts. A refined understanding of winter temperature variability is essential for enhancing climate predictions, supporting climate adaptation strategies, and mitigating societal risks associated with increasing winter temperature variability in South Korea.

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