NOWCASTING CONVECTIVE ACTIVITY FOR SPACE-SHUTTLE LANDINGS DURING EASTERLY FLOW REGIMES

Space shuttle landings at the shuttle landing facility at Kennedy Spac e Center are subject to strict weather-related launch commit criteria and flight rules. Complex launch commit criteria and end-of-mission fl ight rules demand very accurate nowcasts (forecasts of less than 2 h) of cloud, wind, visibility, precipitation, turbulence, and thunderstor ms prior to shuttle launches and landings. During easterly flow regime s the onset of convective activity has proven to be particularly diffi cult to predict. Contrasting weather ranging from clear skies to thund erstorms occurs on days with seemingly similar synoptic environments. Four days of easterly flow during the Convection and Precipitation/Ele ctrification (CaPE) Experiment were investigated in an effort to ident ify and simulate key features that distinguish convectively active and suppressed conditions. Data from CaPE and operational data, including satellite imagery and National Centers for Environmental Prediction m odel analysis output over the Florida peninsula and surrounding data-s parse Atlantic Ocean, are combined in the research. It is found that e levated moisture in the midtroposphere above the marine boundary layer helps distinguish convectively active and passive days. Moreover, ana lysis reveals that the moisture distribution is related to jet dynamic s in the upper troposphere. A series of simulations using the Mesoscal e Atmospheric Simulation System (MASS) model was undertaken. The MASS model run with a coarse grid (45 km) correctly simulates the developme nt of the upper-level jet streak and its general impact on convective activity over the Florida peninsula. The MASS model run with a nested (11 km) grid and moisture enhancement of the initial model state from radar, satellite, and surface data results in the best short-term (6 h ) forecast of relative humidity and precipitation patterns over the Fl orida peninsula and proximate coastal environment. Implications of the research results for nowcasting convective activity over Cape Canaver al are discussed.