Impacts of Eastern Tropical Pacific Sea Surface Temperature Patterns on Winter Precipitation in the United States

ABSTRACT Winter precipitation across the United States is strongly influenced by climate variability in the eastern tropical Pacific, particularly from El Niño‐Southern Oscillation (ENSO). However, ENSO alone cannot fully explain the range of observed precipitation anomalies. This study investigates the influence of sea surface temperature anomaly (SSTA) patterns in the eastern tropical Pacific, identified using cluster analysis, on winter precipitation across the continental US. The SSTA clusters were used to composite precipitation data from the National Centers for Environmental Information and synoptic‐scale variables from reanalysis fields. Cluster 1, most similar to weak El Niño and neutral ENSO, is associated with below‐normal precipitation in the Upper Midwest and wetter conditions in southern California. Cluster 2, most similar to La Niña, shows widespread below‐normal precipitation across the Southwest and Great Plains alongside a wet Southeast. Cluster 3, also resembling La Niña, produces below‐normal precipitation across the southern United States and Mid‐Atlantic and above‐normal precipitation in the Pacific Northwest. Cluster 4, most similar to El Niño, is associated with enhanced precipitation across much of the southern United States, excluding California and drier conditions in the Intermountain West and Midwest. Compared to composites computed from ENSO phases, the SSTA and precipitation clusters exhibit statistically significantly lower internal variability, indicated by reduced standard deviations and overall stronger correlations between composite means and their respective member years. By leveraging thermal wind considerations, this study links cluster precipitation patterns to the meridional displacement of the jet stream via exploration of 250–700 hPa thickness gradient and 250‐hPa jet stream anomalies. These relationships are further supported by corresponding Pacific‐North American (PNA) patterns in the 500‐hPa geopotential height anomalies. The direct association of each cluster's SSTA structure with downstream precipitation, along with synoptic‐scale analysis to explain observed precipitation patterns, enables this approach to provide further insights into wintertime US precipitation variability.