Systematic Model Forecast Errors of Surface Cyclones in NMC's Nested-Grid Model, December 1988 through November 1990

Abstract

Abstract Systematic errors in the nested-grid model (NGM) forecasts of surface cyclones are examined over a two-year period from 1 December 1988 through 30 November 1990. The parameters examined include the location, central pressure, 850-mb temperature, and the 1000-500-mb thickness over the center of the surface cyclone. The mean cyclone position error was typically 150 km at 12 h and 225 km at 24 h, and grew to about 350 km by 48 h. The overall mean cyclone pressure error was −0.57 and −0.68 mb at 24 and 48 h, respectively. The results show that the skill of the NGM forecasts of surface cyclones displayed both seasonal and annual variability. The seasonal variability is represented by overall smaller errors in the summer and larger errors in the winter. The NGM tended to overdeepen surface cyclones in all but the summer months. A large part of the pressure error was due to the model's inability to fill cyclones properly and a tendency to forecast systems to deepen when they were observed to fill. About...