Dynamical Extended Range Forecasting (DERF) at the National Meteorological Center

Abstract

The primary objective of this program is to assess the feasibility of extending operational numerical weather prediction beyond the medium range to the monthly outlook problem. In this paper the principal focus is upon assessment of a contiguous set of 108 thirty-day integrations generated with the then operational Medium Range Forecast model from initial conditions 24 hours apart between 14 December 1986 and 31 March 1987. Results indicate some serious model deficiencies, such as the tendency for zonalization, i.e., systematically stronger midlatidue zonal flow than observed, and a stratospheric cold bias, which continues to grow through the 30-day integrations. Finally, a major finding is that a large component of the variability in forecast skill results from the inability to predict the evolution of blocking events beyond a few days into the forecasts. -from Authors