A nine-layer, primitive equation (PE) model of the global atmosphere developed at the Goddard Institute for Space Studies (GISS) has been used to generate six 48-hr forecasts during December 1972 and January 1973. Operational analyses north of 18N and experimental global analyses made available by the National Meteorological Center (NMC), NOAA, were used as the initial conditions; the operational analyses were used to verify the forecasts at 12-hr intervals over the northern hemisphere north of 22N. The combined analyses were used to verify the forecasts in the global domain.
Root-mean-square errors of the sea-level pressure, 1000-mb heights, and vector geostrophic winds, and 500-mb heights and vector geostrophic winds indicate that the GISS forecasts have skill comparable to those made by operational PE models.
A summary of the 36-hr evolution of extratropical cyclones shows that their speed of propagation is systematically too slow and their central pressures are systematically too high, as has already been documented for the NMC PE model forecasts.
Forecasts of the surface temperature, computed by vertical extrapolation from the model's two lowest levels, and verified quantitatively over North America and qualitatively over the United States, show considerable skill.