Our main objective in this study is to examine the role and importance that boundary-layer and shallow convective clouds have on the evolution of extratropical cyclones. Three types of shallow cloud schemes have been tested in a high-resolution version of the Canadian Global Environmental Multi-scale (GEM) model. The three cloud schemes are based on: i) a statistical approach in which low-level clouds are directly included in the TKE boundary-layer turbulence scheme; ii) a mass-flux methodology which directly represents the effect of subgrid-scale shallow updrafts and downdrafts; and iii) a modified version of a Kuo convective scheme based on moisture accession from the boundary layer and on the rapid dissipation of shallow clouds.

A five day integration has been performed with a 1200 x 800 x 58L version of GEM (i.e., ~ 25 km at 40 degree latitude) and the medium-range evolution of two synoptic-scale weather systems (over the north Pacific and north Atlantic) have been examined. Results on the ability of the three schemes to represent the low-level shallow clouds activity that covered large areas ahead and behind these two systems will be presented at the conference, as well as some insights on how these clouds influence the development of the two extratropical cyclones.