REGIONAL PRECIPITATION VARIABILITY IN THE SOUTHERN UNITED STATES

Seasonal precipitation varies both spatially and temporally across the southern United States. In order to address the causes of the temporal variability, this paper first develops a regionalization of southern precipitation. In all four seasons, five distinct precipitation regions are evident. These five regions differ in size and extent in each season and can be related to the precipitation-generating mechanisms operating at that time of year. Precipitation within each region varies considerably over time. In autumn, seasonal precipitation also displays a significant trend in three regions. The East Coast has experienced a decrease in precipitation, whereas western areas of the study region have become wetter. In order to understand the influence of large-scale circulation on the temporal variability and autumn trends, regional precipitation anomalies are correlated with major atmospheric teleconnection features over North America. Although the traditional mid-latitude teleconnections explain significant portions of precipitation variability, a subtropical index that measured onshore flow from the Gulf of Mexico is more highly correlated with seasonal precipitation. This result indicates that more research is needed on the Atlantic Subtropical High and subtropical circulation before an accurate explanation of precipitation variability in this region is possible. [Key words: climatology, precipitation variability, teleconnections, southern United States.]