Verification of Instability Parameters over the Great Plains from RAP Model Forecast Soundings

In the anticipation of severe convective weather, forecasters often rely on model forecast soundings and derived instability parameters to determine both the likelihood of convective initiation and the severity of any storms that develop. Model solutions are highly dependent on the data assimilation scheme, physics, and parameterizations that are used; thus, forecast soundings and their derived parameters can vary greatly between differing numerical model configurations.

On 1 May 2012, the National Centers for Environmental Prediction (NCEP) implemented the operational Rapid Refresh (RAP) model, which is a replacement for the Rapid Update Cycle (RUC) model. Although verification studies of the RAP were conducted by the Earth System Research Laboratory and the Environmental Modeling Center prior to its operational implementation, instability parameters were not explicitly studied, leaving forecasters with a limited understanding of RAP performance in pre-convective environments. This study examines RAP 12-hour and 6-hour forecasts of CAPE, CIN, and lifted index, and compares these forecasts to all 0000 UTC upper-air soundings in the Great Plains with greater than 500 J kg^-1 of CAPE, between 2 May 2012 and 15 July 2012. Overall trends and biases in these variables, synoptic and mesoscale environments that lead to significant over- or under-estimation of instability, and implications for severe weather forecasting will be discussed.