Toward Convective-Scale Prediction within the Next Generation Global Prediction System

Abstract

The Geophysical Fluid Dynamics Laboratory (GFDL) has developed a new variable-resolution global model with the ability to represent convective-scale features that serves as a prototype of the Next Generation Global Prediction System (NGGPS). The goal of this prediction system is to maintain the skill in large-scale features while simultaneously improving the prediction skill of convectively driven mesoscale phenomena. This paper demonstrates the new capability of this model in convective-scale prediction relative to the current operational Global Forecast System (GFS). This model uses the stretched-grid functionality of the Finite-Volume Cubed-Sphere Dynamical Core (FV3) to refine the global 13-km uniform-resolution model down to 4-km convection-permitting resolution over the contiguous United States (CONUS), and implements the GFDL single-moment 6-category cloud microphysics to improve the representation of moist processes. Statistics gathered from two years of simulations by the GFS and select configurations of the FV3-based model are carefully examined. The variable-resolution FV3-based model is shown to possess global forecast skill comparable with that of the operational GFS while quantitatively improving skill and better representing the diurnal cycle within the high-resolution area compared to the uniform mesh simulations. Forecasts of the occurrence of extreme precipitation rates over the southern Great Plains are also shown to improve with the variable-resolution model. Case studies are provided of a squall line and a hurricane to demonstrate the effectiveness of the variable-resolution model to simulate convective-scale phenomena.

Dependence on initial conditions versus model formulations for medium‐range forecast error variations

“…The GFS physical parametrizations described in the previous section are used in this study, except for the Zhao–Carr grid‐scale condensation and precipitation parametrization which is replaced with the GFDL single‐moment six‐category cloud microphysics (Zhou et al . ). In the most recent version of fvGFS, the EDMF PBL scheme is replaced with the YSU (Yonsei University) PBL scheme (Hong et al .…”

What Is the Predictability Limit of Midlatitude Weather?

“…The newly developed Geophysical Fluid Dynamics Laboratory (GFDL) FV3 with Global Forecast System (GFS) physics (fvGFS) modeling system (Zhou et al 2019;Hazelton et al 2018;Chen et al 2018) is used to further cross-examine the sensitivity of multiscale predictability to different model parameterizations and resolutions under future global convection-permitting NWP. This system was built during the NGGPS phase II, using the nonhydrostatic FV3 coupled to physical parameterizations from the National Centers for Environmental Prediction's GFS (NCEP/GFS).…”

Explicit Prediction of Continental Convection in a Skillful Variable‐Resolution Global Model

“…Further development will entail introduction of modern physics packages, especially revisions to the microphysics and planetary boundary layer scheme, and improvements to the initialization, including radar and satellite data assimilation. Some initial results of these developments are described in Zhou et al () and Zhang et al ().…”

“…Further development will entail introduction of modern physics packages, especially revisions to the microphysics and planetary boundary layer scheme, and improvements to the initialization, including radar and satellite data assimilation. Some initial results of these developments are described in Zhou et al (2019) and Zhang et al (2019).The manuscript is organized as follows. Section 2 describes the cfvGFS model and its configuration for the simulations described in the rest of the manuscript.…”

“…Section 5 summarizes the paper and discusses the prospects for a unified modeling system.The GFS physics used for the simulations described here use the most recent scale-aware Simplified Arakawa-Schubert (SA-SAS; Han et al, 2017) shallow and deep convection schemes; the GFS planetary boundary layer scheme (Han & Pan, 2011); and the Rapid Radiative Transfer Model (Clough et al, 2005). The simple single-condensate microphysics scheme of Zhao and Carr (1997) and cloud fraction scheme of Xu and Randall (1996) used in the operational GFS is replaced by the GFDL six-category microphysics and cloud fraction scheme (Chen & Lin, 2013;Zhou et al, 2019) augmented with the ability to perform phase changes and latent heating at a faster timescale than the rest of the physical parameterizations. The total ice condensate and total liquid condensate, including precipitating hydrometeors, are passed separately to the radiation scheme.…”