An Analysis of Heavy Rainfall Weather Systems over Louisiana

This study was conducted as a Partners Project between the University of Louisiana at Monroe, Louisiana and the National Weather Service Forecast Office in Shreveport, Louisiana. Heavy precipitation events that produce extreme amounts of rainfall occasionally occur over Louisiana and neighboring southern states. Four case studies that produced significant amounts of rainfall in 2006 and 2008, primarily over Louisiana, were analyzed using the National Weather Service's Weather Event Simulator (WES) software, for synoptic and mesoscale features to determine causes of excessive rainfall. These extreme rainfall events were responsible for significant disruption of normal day-to-day activities due to flash flooding over large parts of Louisiana. Three out of the four cases related to upper level troughs or cyclones, while the other case was related to Hurricane Gustav (2008) making landfall and tracking over north Louisiana and southwest Arkansas. The analysis showed important structural and evolutionary differences between the cases that enabled the systems to produce heavy rainfall. A common feature between the cases was a moisture plume that was advected around either an upper level system or a tropical cyclone. This pool of enhance moisture combined with an already unstable environment and a slow moving weather system, to create an environment favorable for excessive rainfall.