Observations of Moisture Increases During the Southern Great Plains Afternoon to Evening Transition

Each spring, the U.S. Southern Great Plains (SGP) hosts a wide variety of ingredients (e.g. moisture, shear, instability, and lift) relevant to deep, moist convection.  Tracking the spatiotemporal evolution of these ingredients is critical to understanding the initiation, maintenance, and demise of deep, moist convection.  In the case of the afternoon to evening transition (AET), changes to these ingredients can be quite significant.  Various investigators have found that during the AET, rapid increases in low-level shear and stability occur.  However, this model offers conflicting answers to the question of convective evolution.  While increases in low-level static stability during the AET may act to destroy deep convection, increases in low-level shear may promote the development and maintenance of updrafts.  Consideration of only these two ingredients offers an incomplete and conflicting conceptual model of how AET environmental changes may impact the behavior of ongoing deep convection.

A little-known change that also occurs around sunset is that rapid increases (~1 g/kg) in low-level moisture also occur.  Although past studies have documented these changes in other geographical regions and quiescent environments, they have not been studied in the SGP nor in the context of deep, moist convection.  These rapid changes may also act as a mechanism to intensify and/or promote deep, moist convection.  The experiments described by this presentation aim to characterize how changes in convective ingredients occur during the AET by using data from high-temporal resolution instruments deployed in the SGP (e.g., ARM, Oklahoma Mesonet, PECAN).  Particular attention will be paid towards characterizing the AET moisture changes and identifying cases where such moisture changes may cause a rapid increase of convective instability.  Recognition of when and where these moisture changes occur may help operational forecasters better anticipate how convection may evolve around sunset.