The Mackenzie GEWEX Study (MAGS) regional climate modeling system (denoted CRCM-MAGS) is a developmental version of the Canadian Regional Climate Model (CRCM) tailored for use over North America. It is composed of three major components: the dynamical kernel of the CRCM, the operational physical parameterization package of the Canadian Centre for Climate Modelling and Analysis (CCCma) atmospheric general circulation model (GCMIII), and a high resolution land surface database developed for MAGS. In addition, surface runoff can be routed offline using the WATFLOW hydrologic model and a drainage database constructed over North America for the CRCMMAGS. Although closely related to the CRCM, the CRCM-MAGS differs in several major aspects. The Mackenzie Basin climate from a five year (plus 21 month spin up period) simulation was evaluated against surface observations. The model simulates a mean annual precipitation bias of about 13%, and a cold surface temperature bias of less than 1 ° C in both summer and winter. These results suggest that the GCMIII physics package, developed for a relatively coarse resolution GCM, can be used successfully in a high resolution regional climate model with minimal modification, provided a realistic surface representation is included.