A New Operational Global Ensemble from the U.S. Air Force

Recently, the United States Air Force (USAF) entered into the United Kingdom Met Office’s worldwide partnership utilizing the Unified Model (UM) for operational global numerical weather prediction. The USAF’s local instantiation of the UM is a modeling suite called the Global Air-Land Weather Exploitation Model (GALWEM). A global ensemble (GE) utilizing the GALWEM suite was designed to largely match the other operational global ensembles within the National Earth System Prediction Capability (ESPC) to allow for its contribution to the ESPC national unified ensemble (NUE) via public hosting of its members in real-time on the NOAA NOMADS web server.

GALWEM-GE has a native horizontal resolution of 40 km and 70 vertical levels, with gridded output on a half-degree lat/lon grid. 21 ensemble members are initiated on the 00 and 12Z cycles using ETKF as part of a hybrid 4DVAR data assimilation system, along with SST and soil moisture perturbations. Model uncertainty is accounted for with Stochastic Kinetic Energy Backscatter, random parameters, and stochastic physics packages. Initial testing indicates that adding GALWEM-GE to the NUE consistently increases its forecasting skill as measured by the Continuous Ranked Probability Score for a variety of forecast variables at multiple forecast lead times, giving confidence that the addition of GALWEM-GE to NUE will bring a positive operational impact for forecasters and decision makers who utilize it.