On March 22, 2021, NOAA announced that the National Weather Service (NWS) would use a new global computer model for weather forecasts. This is an “under the hood” type of improvement that most voyagers won’t see directly. If the new system works as advertised, however, voyagers should see better weather forecasts on their vessels.
NOAA says the new Global Forecast System (GFS) “will increase forecast capabilities across the U.S. These advancements will improve hurricane genesis forecasting, modeling for snowfall location, heavy rainfall forecasts, and overall model performance.”
The GFS is a numerical weather prediction model that uses a mathematical model of the atmosphere to predict the weather. The model uses differential equations involving fluid motion, thermodynamics, radiative transfer, chemistry and other factors. The globe is divided into grids and inside each grid the winds, heat transfer, solar radiation, relative humidity, phase changes of water and surface hydrology are calculated for each grid cell. Then the interactions between cells are also calculated to predict future conditions. These grid cells are well known to voyagers as they are the basis for the gridded binary or GRIB file. A GRIB file is a collection of self-contained records of 2D data. Each GRIB file can be individually accessed, or a group of files can be assembled to display an area.
Each of the major meteorological services has its own numerical computer model. For example, the UK Met Office has a model called UM, Meteo-France uses a model called ARPEGE, the European Centre for Medium-Range Weather Forecasts has a model called ECMWF (widely considered to be the best global weather model), while the China Meteorological Administration uses a model dubbed GRAPES_GFS V3.1.
The improved forecasts produced by this new version of NOAA’s GFS are the result of a number of changes to the system. One change is to include more levels of the atmosphere — from 64 to 127. The model also uses data from higher levels in the atmosphere. The new data set reaches to 50 miles high, allowing the model to better describe the position of the jet stream, a prime factor in steering the direction of storms. There will also be improvements to atmospheric physics that will enhance snow and precipitation forecasting capabilities. Another improvement touted by NOAA involves ocean waves: “…GFS will be coupled with a global wave model called WaveWatch III which will extend current wave forecasts from 10 days out to 16 days and improve the prediction of ocean waves forced by the atmosphere. Coupling the GFS and wave models will streamline the National Centers for Environmental Prediction (NCEP) production suite by consolidating atmospheric and wave forecast data and distributing them together.”
According to NOAA this new version of the GFS was run for a 31-day test run, and during one eight-day period it was more accurate than the European ECMWF. On balance, though, the European model keeps its reputation for accuracy.
Any numerical model is only as good as its data. In addition to updating the algorithms of the GFS model, NOAA is also upgrading its data collection effort. That data comes in via the Global Data Assimilation System (GDAS) and the modernization of GDAS will allow the model to pull in more data from satellites and from aircraft.
“These upgrades are part of the Next Generation Global Prediction System within the Unified Forecast System (UFS) framework, which is an ongoing effort to leverage the expertise of the broader weather community and expedite the research to operations pathway,” said Vijay Tallapragada, Ph.D., chief of the Modeling and Data Assimilation Branch at NOAA’s Environmental Modeling Center.
These improvements mark the first major upgrade to what NOAA calls “the Finite-Volume Cubed-Sphere (FV3) dynamical core-based GFS” since June 2019. The GFS with the FV3 dynamical core “…brings together the superior physics of the global atmosphere with day-to-day reliability and speed of operational numerical weather prediction.”
These changes should mean better GRIB data and better forecasts.