Sea Surface Salinity as a Subseasonal Predictor for Summer Precipitation in the Midwest

The Midwest region has particularly low skill in weather and climate prediction compared to other regions of the United States. Additionally, summer precipitation in the Midwest can be the result of various factors because of the variability of precipitation sources in that region. This research investigates how oceanic predictors, specifically sea surface salinity in the tropical and North Atlantic regions, can serve as a source of subseasonal-to-seasonal predictability to improve summertime U.S. Midwest precipitation forecasts.

As freshwater evaporates from the ocean, saltier sea waters are left behind. Thus, ocean regions with a positive sea surface salinity anomaly (SSSA) indicate moisture source regions that can be used as predictors for seasonal climate forecasting of terrestrial precipitation. Using the Community Earth System 2- Large Ensemble model output, this research finds that a positive SSSA pattern in the Caribbean Sea and the Gulf of Mexico reveals anomalously positive precipitation in the Midwest four weeks later. In contrast, a negative salinity anomaly in the Caribbean Sea and the Gulf of Mexico reveals an anonymously negative precipitation pattern in the Midwest four weeks after. These results indicate a potential source of predictability for summer Midwest precipitation from the Gulf of Mexico and the Caribbean Sea. It is hypothesized that the evaporated moisture is transported to the Midwest by the Caribbean Low-Level Jet to the Great Plains Low-Level Jet. Thus SSSAs could be used as a predictor for summertime Midwest precipitation on a subseasonal-to-seasonal timescale.