This technical note (TN) describes the automated analysis/forecast model system that currently exists at the Air Force Global Weather Central (AFGWC). The emphasis will be on the interrelation and ing of the various analysis/forecast models in the production cycle. This description of the automated analysis/forecast system was written for managers, programmers, computer operations personnel, users of the ultimate products, and the meteorological community at large. This TN will only address analysis/forecast models that are the primary meteorological data-base builders. Most applications programs that access the data bases are therefore not included.

Using forecast relative humidity (RH) from a global model, several pre-existing diagnostic RH-to-cloud schemes were tested to forecast global fractional cloud cover in a postprocessor format. Since none of the schemes tested provided a superior cloud forecast when compared to Air Force Global Weather Central's (AFGWC) operational 5LAYER cloud forecasts, a new RH-to-cloud scheme was developed by relating cumulative frequencies of forecast RH to cumulative frequencies of analyzed cloud cover from the AFGWC RTNEPH cloud analysis. This scheme creates a series of forecast time-dependent RH-to-cloud curves that can be temporally updated to account for changes in season, cloud analysis, or forecast model, The global model used was a spectral-type developed by the Geophysics Laboratory (GL) using parameterized diabatic physics presently incorporated in the operational GSM (global spectral model) at AFGWC.

AFGWC has three cloud forecast models: Five-Layer (5LAYER), High Resolution Cloud Prognosis (HRCP), and Tropical Cloud Forecasting Model (TRONEW). These models satisfy a wide range of requirements and have been in operation since the early 1970s. The 5LAYER model makes extra-tropical forecasts for periods up to 48 hours. Forecasts of layer and total cloud, cloud type, layer temperatures, and icing and weather conditions are made. The 5LAYER model uses a quasi-Lagrangian approach to make these forecasts. The trajectories needed for these forecasts are computed from the AWS Global Spectral Model (GSM) derived wind forecasts. The 5LAYER moisture is initialized from the Real-Time Nephanalysis Model (RTNEPH) layer cloud-amount and the Multi-layer Analysis Model (MULTAN) layer dew-point depression. The 5LAYER temperatures are initialized from the High Resolution Analysis System (HIRAS) and GSM derived temperatures. The High Resolution Cloud Prognosis (HRCP) model combines RTNEPH analyzed cloud input with 5LAYER trajectories to produce high resolution (25 nm), short-range (out to 9 hour) cloud forecasts. The TRONEW model uses the analyzed RTNEPH cloud to make 24 hour persistence cloud forecasts for the tropics.

A limited area seven layer physical-numerical model for the lower tropospheric region is described. The grid interval is half that of the standard numerical weather prediction grid used in the hemispheric, free atmospheric operational model at the Air Force Global Weather Central (AFGWC). This model is an integral part of the complete AFGWC meso-scale (sub-synoptic) numerical analysis and prediction system. This model provides greater horizontal and vertical resolution in both the numerical analyses and numerical forecasts. It is used to predict the more detailed smaller scale atmospheric perturbations which are important in specifying sensible weather elements. Important features of this boundary layer model include: a completely automated objective numerical analysis of input data; the transport of heat and moisture by three dimensional wind flow (including terrain and frictionally induced vertical motions); latent heat exchange in water substance phase changes; and eddy flux of heat and water vapor. (Author).

Describes the numerical analysis and forecast models most widely used by U.S. Air Force meteorologists. These models are: the Air Force Global Weather Central (AFGWC) Global Spectral Model (GSM); the AFGWC Real-Time Nephanalysis (RTNEPH); the AFGWC High Resolution Analysis (HIRAS) model; the AFGWC Five-Layer cloud forecast model (5-LAYER); the National Meteorological Center (NMC) Nested Grid Model (NGM); and the NMC Aviation/Medium Range Forecast (AVN/MRF) model. Report also describes model grids and tells how the grids are built. Strengths and weaknesses of the various models are discussed, along with AFGWC and NMC production cycles.