The dynamical properties of ECMWF operational forecasts corrected by a (linear) Model Output Statistics (MOS) technique are investigated, in the light of the analysis performed in the context of low-order chaotic systems (Vannitsem and Nicolis, 2008). On the basis of the latter work, the respective roles of the initial condition and model errors on the forecasts can be partly disentangled. For the temperature forecasted by the ECMWF model over Belgium, it is found that: (i) The error ampli cation arising from the presence of uncertainties in the initial conditions dominates the error dynamics of the 'free' atmosphere; (ii) the temperature at 2 meters can be partly corrected by the use of the (linear) MOS technique (as expected from earlier works), suggesting that model errors and systematic initial condition biases dominate at the surface. In the latter case, the respective amplitudes of model errors and systematic initial condition biases corrected by MOS depend on the location of the synoptic station. In addition, for a 2-observable MOS scheme, the best second predictor is the temperature predicted at 850 hPa in the central part of the country, while for the coastal zone, it is the sensible heat ux entering in the evolution of the surface temperature. These di erences are associated with a dominant problem of vertical temperature interpolation in the central and east parts of the country and a di culty in assessing correctly the surface heat uxes on the coastal zone. Potential corrections of these problems using higher resolution models are also discussed.