Regional Forecasting System Research Articles

The Limited-Area Forecast Systems at the Central Weather Bureau in Taiwan

The Central Weather Bureau (CWB) in Taipei, Republic of China has entered the era of operational numerical weather prediction with the complete online operations of a Global Forecast System (GFS) and the Limited-Area Forecast Systems (LAFS). A brief description of the Regional Forecast System (RFS) and the Mesoscale Forecast System (MFS) of the LAFS are presented in this paper. The RFS has a horizontal resolution of 90 km, depends on the GFS for boundary values, and produces forecast up to 48 h over the eastern parts of Asia and the northwestern Pacific Ocean. The MFS has a resolution of 45 km, uses RFS analysis and forecast as initial and boundary conditions, and produces 24-h forecasts for Taiwan and its immediate vicinity. Model configurations, numerics, physical parameterizations, performance statistics, and two significant weather cases of the two forecast systems are discussed. Future improvements and new plans will also be given.

Changes to NMC's Regional Analysis and Forecast System

Abstract The recent implementation of changes to the National Meteorological Center's (NMC's) Regional Analysis and Forecast System (RAFS) is described. The changes include an expansion of the innermost grids of the nested-grid model (NGM) and the implementation of the Regional Data Assimilation System (RDAS). The new version of the forecast model and a 3-hourly RDAS analysis system were implemented on 7 August 1991. Some results from tests of the revised forecast model and the combined RDAS/NGM system are presented.

Evaluating the Impact of RAFS Changes on the NGM-Based MOS Guidance

Abstract In the spring of 1990, the National Meteorological Center (NMC) tested several modifications to the Regional Analysis and Forecast System (RAFS). In order to compare the proposed version of the RAFS to the current operational RAFS, NMC ran both systems in parallel for a 4-week period. Simultaneously, the Techniques Development Laboratory (TDL) applied the operational RAFS-based Model Output Statistics (MOS) equations to output from both the operational and proposed (parallel) versions of the Nested Grid Model (NGM) to generate two sets of MOS forecasts. Our goal was to determine the impact of RAFS modifications on the NGM MOS forecasts. At the end of the 4-week test period, we verified both the operational and parallel NGM MOS forecasts. Virtually no differences in accuracy or skill existed between the operational and parallel MOS forecasts of max/min temperature, probability of precipitation, and surface wind. The skill of the cloud amount forecasts, however, deteriorated significantly. The NGM ...

Some Comparisons of VAS and Dropwindsonde Data over the Subtropical Atlantic

Abstract Omega dropwindsonde and other in situ (INS) data collected during the NOAA/Hurricane Research Division's (HRD) Hurricane Field Program are used as a ground truth dataset for the evaluation of VISSR Atmospheric Sounder (VAS) soundings over the subtropical Atlantic. The experiments were coordinated with the Cooperative Institute for Meteorological Satellite Services at the University of Wisconsin. The focus of this study is to determine whether soundings derived from VAS radiances are an improvement over the first-guess data used as a starting point in the sounding retrieval process. First guess inputs for this study are provided by NMCs Regional Analysis and Forecast System (RAFS) nested grid model (NGM). In a case study, an objective algorithm is used to analyze the INS, VAS, and first-guess data at and below 500 mb from an HRD experiment on 1–2 September 1988. The case study is supplemented by a statistical investigation of data composited from other HRD experiments. In particular, we examine VA...

A Synoptic Evaluation of Normal Mode Initialization Experiments with the NMC Nested Grid Model

Abstract The Regional Analysis and Forecast System at the National Meteorological Center consists of an optimum interpolation objective analysis scheme, an adiabatic nonlinear normal model initialization (NNMI) and a hemispheric Nested Grid Model (NGM) to provide 48 h forecasts. We investigate here the effect NNMI has on the analyses and forecasts produced by this system. An eight vertical mode NNMI procedure led to significant reductions of the divergent component of the analyzed wind field in regions of heavy precipitation. This is shown to contribute to a systematic spinup error in NGM 0–12 h precipitation forecasts, especially from the 0000 UTC runs. Forecasts starting with no initialization had unacceptable noise levels. NNMI using two vertical modes yielded the best combination of noise-free forecasts and unsuppressed initial precipitation rates. A physical interpretation of this result is provided using the vertical structure functions of the normal modes. Tests of the two-mode NNMI in an operation...

The Effect of Snow Cover on the Regional Analysis and Forecast System (RAFS) Low-Level Forecasts

Abstract The response of the Regional Analysis and Forecast System (RAFS) low-level forecast fields to the geographical distribution of snow cover is discussed. The errors produced by an improper specification of this field in the forecast model can have a wide variety of local forecasting implications, ranging from poor forecasts of lee-side Great Lakes snowfalls, to errors in forecasts of the earth's surface temperature in areas where the snow cover is changing rapidly. The use of the snow-cover data in the forecast model and its effect on forecast guidance are described.

The National Meteorological Center Regional Analysis System

Abstract The National Meteorological Center (NMC) Regional Optimum-Interpolation (ROI) analysis is described. The ROI is the analysis component of the Regional Analysis and Forecast System (RAFS) and is specially designed to provide initial conditions for the Nested Grid Model (NGM), the forecast component of the RAFS. The ROI is an attempt to overcome weaknesses in the Limited-area Fine Mesh (LFM) and Global Optimum-Interpolation (GOI) analysis systems, to provide the NGM with more detailed and balanced analyses and to do so in a three-dimensional and dynamically consistent manner. Among the unique aspects are its hemispheric domain with regional-scale (150–200 km) horizontal resolution and improved vertical resolution (16 levels with the first 12 below 250 mb). The analysis is geostrophically coupled and is multivariate in geopotential and wind; it utilizes the same sigma coordinate as the NGM prediction model. All significant-level radiosonde data are now used, as well as many more of the surface obser...

Description and Evaluation of NORAPS: The Navy Operational Regional Atmospheric Prediction System

Abstract A complete regional forecast system (NORAPS) has been developed for the Navy. The forecast grid is globally relocatable and can be set to any size and resolution. NORAPS performs wind and mass analyses, a static initialization, and computes a terrain field for whatever grid is chosen. The forecast model includes an efficient time integration scheme, cumulus parameterization, large-scale precipitation, latent and sensible heat fluxes over water, and one-way interactive boundaries. NORAPS was tested on 30 forecasts over the Mediterranean region. Average objective scores for these forecasts indicated NORAPS represented an improvement over the current Fleet Numerical Oceanography Center's hemispheric model. One case of strong cyclogenesis was rerun with 10 levels instead of the 5 used in the original run. Improvements were noted in the forecast intensity and intensification rate.