Total and Planetary-Scale Systematic Errors in Recent NMC Operational Model Forecasts

Abstract

The total and systematic errors in the 500 mb geopotential height forecasts from the NMC grid-point and spectral operational models are compared and contrasted for two recent winters. The spectral model is shown to be an improvement in the forecasts through a more skillful prediction of the planetary-scale (zonal wavenumbers 1-2) quasi-stationary wave amplitudes, and through the elimination of the grid-point model's large systematic error at low latitudes. In agreement with estimates from related studies, the systematic error in the NMC spectral model accounts for 15-20% of the total error variance. Approximately one-half of the total systematic error resides in the planetary scales.