The La Plata basin (LPB), located in southeastern South America (SESA), is a region of significant socioeconomic importance, particularly for agriculture. This area of South America exhibits strong land-atmosphere coupling in the warm season. In this work, we evaluate the impact of large-scale soil moisture (SM) anomalies on regional-scale atmospheric conditions. Multivariate empirical orthogonal function (EOF) analysis is used to extract the dominant modes of joint variability of monthly averaged root-zone SM and one month-lagged precipitation from atmospheric reanalyses. We find that the dominant EOF pattern is consistent with a positive correlation between antecedent SM and precipitation, while the second dominant EOF pattern is consistent with a negative correlation between these variables. To evaluate causality, the effects of large-scale SM anomalies on atmospheric variables are examined using the Community Earth System Model (CESM). CESM simulations suggest that anomalously dry SM is initially co-located with decreased precipitation. Subsequent changes in the atmospheric circulation associated with a thermal low draw moisture into the region, eventually promoting increased precipitation. This study investigates the pathways through which SM anomalies modulate precipitation in this region. For this reason, this study has potential atmospheric prediction applications which could benefit the population and the socioeconomic well-being of this important region.