IBM GRAF—Scale-Aware Convective Forecast Evaluation and Improvements

IBM GRAF - Scale-Aware Convective Forecast Evaluation and Improvements

Wilt, Brett, The Weather Company, an IBM Business

Wei Wang, National Center for Atmospheric Research

In August 2018, The Weather Company (TWC), an IBM Business, implemented a custom version of the NCAR Model for Prediction Across Scales (MPAS). The initial model configuration utilized MPAS 5.2 Kain-Fritsch convection physics, operating on a uniform 15-km resolution mesh with 72 forecast hours (experimentally 144 hrs for research purposes).

With the recently announced IBM GRAF (Global High-Resolution Atmospheric Forecasting System) development goals, the hourly-updating variable resolution (15/3-km) MPAS mesh introduces the requirement for scale-aware convection physics. Upon review of several convective parameterizations, a Tiedtke-based approach was selected to compliment numerous convective aspects of the GRAF application, including data-assimilation, statistics, visual representation, tropical, pattern recognition, etc.

An overview of GRAF-Tiedtke scale-aware progress will be discussed, along with supporting results and comparisons from a 50 case reforecast lab environment. As verification examples of the lab environment, a baseline of 2-meter temperature, 10-meter wind RMSE and bias statistics are computed for approximately 3000 METAR sites across the continental United States (CONUS). General precipitation metrics, such as Equitable Threat Score (ETS), Fractions Skill Score (FSS), and Critical Success Index (CSI) will also be presented. In addition to the lab statistics, applying basic scale-aware logic to Tiedtke convection schemes provides valuable information for other critical scale-aware aspects, including tropical convection across mesh boundaries, tropical cyclone tracks, and 5-6 day synoptic scale pattern comparisons.