An anonymous reader quotes a report from Ars Technica: For the first time in about 40 years, the guts of the U.S. model got swapped out for something new today. The upgrade brings us a new “Finite-Volume Cubed-Sphere” (or FV3) dynamical core, which simulates the basic atmospheric physics at the heart of this endeavor, a change that has been in the works for a while. The new core had its origins in simulating atmospheric chemistry but ended up being adapted into other models. A few years ago, it was selected to replace the old core in the U.S. Global Forecast System model. And for more than a year now, the new version of the model has been running in parallel so its results could be compared to the operational model.
The results have been a little mixed. The new core improves computational efficiency and allows some processes to be simulated at a higher resolution — unequivocal improvements. It also simulates the physics of water vapor more realistically. In a press conference today, NOAA scientists cited a number of areas where forecast improvements have been seen. Forecast tracks of hurricanes and the mid-latitude storms that frequently sweep across the U.S. have both improved, they said, along with forecasts of hurricane strength. Forecast precipitation amounts were also cited as a key area of progress. But there have also been grumblings in the weather community over the past year about results that didn’t seem so hot. For example, surface temperatures have been biased low in some situations, throwing off forecasts.