Dryness over the US Southwest, a Springboard for Cold Season Pacific SST to Influence Warm Season Drought over the US Great Plains

Although the influence of sea surface temperature (SST) forcing and large scale teleconnection on summer droughts over the United States (US) Great Plains has been suggested for decades, the underlying mechanisms are still not fully understood. Here we show a significant correlation between a low-level moisture condition over the US Southwest in spring and rainfall variability over the Great Plains in summer. Such a connection is due to the strong influence of the Southwest dryness on the zonal moisture advection to the Great Plains from spring to summer. This advection is an important contributor for the moisture deficit during spring to early summer, and so can initiate warm season drought over the Great Plains. In other words, the well documented influence of cold season Pacific SST on the Southwest rainfall in spring, and the influence of the latter on the zonal moisture advection to the Great Plains from spring to summer, allows the Pacific climate variability in winter and spring to explain over 35% of the variance of the summer precipitation over the Great Plains, more than that can be explained by the previous documented West Pacific-North America (WPNA) teleconnection forced by tropical Pacific SST in early summer. Thus, this remote land surface feedback due to the Southwest dryness can potentially improve the predictability of summer precipitation and drought onsets over the Great Plains.