Past studies show that CPSs struggle with predicting precipitation for warm-season events with weak large-scale dynamic forcings. The WRF model was used to investigate the different CPSs and how they handle warm-season convection. An idealized supercell case, examined at grid spacings of 2 and 4 km with all three schemes, showed that all the schemes, except the Grell-Devenyi ensemble, simulated classic supercellular features with varying degrees of success. At 4 km, the no-CPS simulation represented convection explicitly demonstrating that a CPS might not be needed at 4 km grid spacings.
The 28-29 July 2005 summertime convective system with weak synoptic-scale forcings that occurred in South Dakota and Nebraska was simulated using a 12 km spacing to represent current operational model grid spacings and a 4 km spacing to determine if the WRF model could resolve the convection explicitly. The WRF model was unable represent convection explicitly at 4 or 12 km and needed a CPS to represent sub-grid scale precipitation. The only CPS unable to simulate precipitation was the Betts-Miller-Janjic scheme due to the dryness of the environment. The Kain-Fritsch scheme represented the isolated nature of the system at 4 km, while Grell-Devenyi could only simulate the general area. All three CPSs performed consistently at both grid spacings. This study demonstrates that the use of a CPS in a numerical model is not clearly defined and caution needs to be employed when choosing whether or not to use a CPS and which one.
Supplementary URL: http://weather.unl.edu/~crowe/AMS2007