Atmospheric circulation and moisture budget drivers of dominant modes of winter extreme precipitation variability over North America

Multi-day winter precipitation events can trigger hazards like flooding and landslides. This study identifies dominant modes of variability—and large-scale dynamical, thermodynamical, and moisture budget drivers—of monthly maximum consecutive 5-day precipitation extremes (Rx5day) across North America (NA) during extended winter months (November–March, 1961–2023). Three dominant modes of Rx5day variability, collectively accounting for 30.7% of total variance, are identified from two global reanalysis datasets (ERA5 and JRA-55) using common Empirical Orthogonal Function (EOF) analysis. Distinct positive and negative anomaly centers are found across western and eastern NA. The three modes are primarily driven by large-scale atmospheric circulation anomalies, extending from the North Pacific across NA to the North Atlantic, and atmospheric moisture anomalies, particularly wind-driven moisture transport concentrated in the lower troposphere (surface to ~ 500 hPa). This is reflected in anomalous westerly and southerly flows bringing moisture from the Pacific into western NA and from the Gulf of Mexico into southeastern NA, where upward motion and deep tropospheric moisture columns enhance extreme precipitation. Moisture budget analysis reveals that moisture flux convergence primarily supplies moisture for these extreme events, with local evaporation playing a minor role. Specifically, convergence of mean moisture by transient winds emerges as the primary driver of extreme precipitation variability, with its contribution often exceeding that of total moisture flux convergence. Moisture budget components at 850 hPa closely reflect their vertically integrated counterparts, indicating the pivotal role of the lower troposphere in large-scale moisture transport and convergence processes for extreme precipitation.