The formation of major northern hemisphere blockings during January 1979 is studied in numerical simulations of the global atomosphere with a sea surface temperature (s.s.t.) field updated with observations during the model integration. Both the standard 4 x 5 degrees latitude-longitude and high-resolution 2 x 2-5 degrees versions of the Goddard Laboratory for Atmospheres general circulation models (GCMs) are employed. The s.s.t. field is provided by a blend analysis of in situ and satellite-retrieved data.The simulations by the high-resolution GCM with a realistic s.s.t. field of the ocean surface are shown to be capable of producing two successive realistic major blockings in the Pacific and Atlantic through a onemonth period. The skill in predicting the blocking formation as obtained in the simulations is due to improved skill in forecasting of ultralong waves. Although the results are encouraging, only one initial state is involved in this series of simulations; therefore, the results should not be generalized yet at this stage of investigation.