Spring to Summer Transitions in the Missouri Ozarks Region

The seasonal transition from spring to summer is often very abrupt in the eastern Missouri Ozarks. The warm,humid,periodically wet regime of late spring quickly transitions to a hot humid condition accompanied by infrequent precipitation. This transition can be described dynamically as the change-over from a baroclinic environment to an equivalent barotropic flow regime. Climatologically, the summer season is drier than spring in the Midwest,and the precipitation that does occur often results from infrequent bursts of intense precipitation fron convective events. This work seeks to identify the transition to a summer flow regime using 81 years of daily data from nine cooperative observing sites of the National Weather Service in the Missouri Ozarks. Analysis of daily temperature and precipitation records will be employed to develop criteria identifying the onset of the transition to summer. Relationships to the North American monsoon, Caribbean and Central American mid-summer dry prriod, transition to an easterly 500 millibar flow in the tropics, ablation of the North American snow cover,and interannual variations in the climate system due to ENSO will be considered. The investigation will conclude with an analysis of the predictability of the onset and nature of the summer season in the Missouri Ozarks,with comparison to predictability of the North American monsoon,employing tropical and mid-latitude sea surface temperatures in the Pacific.