The southern Great Plains (SGP) of the United States is a region of strong subseasonal variability of warm season precipitation. Previous studies using General Circulation Models (GCMs) coupled with Land-Surface Models (LSMs) have indicated a particularly strong sensitivity of subseasonal precipitation to soil moisture conditions over the SGP. The goal of the current study is to use a high resolution coupled LSM/convection-resolving atmospheric model to explictly examine how the land-surface conditions can systematically impact SGP warm-season precipitation through through their interaction with the overlying planetary boundary layer (PBL).

Subcontinental scale simulations using the coupled Weather Research and Forecast (WRF)/LSM model are integrated for 12 days during the convectively active International H20 Experiment (IHOP) period from 9 to 21 June 2002. A control simulation that utilizes fine-scale high resolution land surface initial conditions and incorporates a two-way feedback between the atmosphere and the land surface produces realistic time-averaged PBL conditions and precipation following the afternoon diurnal heating cycle. Results indicate that both advection and evaporation contribute strongly to daytime increases in convective available potential energy (CAPE) and subsequent evening precipitation over the SGP. Preliminary analyses of additional simulations, including one using a climatological time-invariant soil moisture condition, have indicated sensitivity in both the diurnal evolution of CAPE and precipitation to differences in land-surface atmosphere interactions among the simulations. These differences will be examined further and discussed at the conference.