A two-level spherical quasi-geostrophic model is used to assess the dependence of model skill upon initial conditions. The medium-frequency variability of a 3600-day control run of perpetual January conditions is found to exhibit many features of the observed wintertime circulation in the Pacific sector. In particular, the frequency of occurrence and characteristics of quasi-stationary regimes, periods when the planetary circulation is more persistent than usual, are similar to those observed. A total of 856 predictability experiments are performed by introducing small initial errors to the control run. Quasi-stationary flow patterns in the Pacific sector are no easier to predict than transient flow patterns. In addition, forecasts begun during quasi-stationary periods are no more successful than those begun during transient episodes. An index of the dominant medium-frequency variability of the control run, a north-south dipole in the eastern Pacific, is used to assess the dependence of model skill on the strength of the zonal flow across the Pacific Ocean. We found a slight asymmetry in forecast skill, such that forecasts begun during episodes of above-normal zonal flow are more successful than those begun during episodes of below-normal zonal flow. These results are consistent with recent analyses of European Center for Medium Range Weather Forecasts model forecast skill. ¿ American Geophysical Union 1988