Figure 1:

24 hour precipitation as observed at the Toronto Airport during a 2-year period and as simulated by two generations of the CCCma atmospheric general circulation model at a grid point near Toronto.  The diagram demonstrates that these GCMs simulate precipitation variability that is similar to that which is observed.  The more recent version of the model (AGCM3) appears to produce smaller precipitation extremes at this particular location that the earlier version of the model. Scale considerations suggest that models should simulate smaller precipitation extremes than observed, and that there should be increasing agreement as the resolution of the model increases.