Development of the 35‐km version of the Canadian regional forecast system

Abstract

A new, higher‐resolution version of the regional forecast system was implemented into operations at the Canadian Meteorological Centre during 1995. The new version of the regional finite‐element forecast model is run at 35‐km resolution in the horizontal and 28 sigma levels in the vertical (instead of 50‐km and 25 levels in the previous operational version), with a more advanced physics package. The improved physical parametrizations feature the following: 1) modifications to the treatment of surface processes; 2) changes to the surface layer formulation; 3) an explicit cloud scheme following Sundqvistfor stratiform precipitation; 4) Fritsch‐Chappell scheme for deep convection. The new regional forecast system also includes a pseudo‐analysis of initial soil moisture content based on model error feedback. Both objective and subjective evaluations on case studies and in the parallel runs showed improved performance with the new 35‐km model. The main points from these verifications indicated a significant reduction of the moist bias near the surface, improvements in the predicted surface temperatures and the diurnal cycle, better forecasts of convective precipitation, and more realistic surface wind forecasts, especially over complex orography due to the increased resolution. The new predicted cloud parameters permit a better representation of the cloud‐radiation interactions that are important for the atmospheric energy balance, especially at the surface.