ECMWF And GFS Models Disagree, Forecaster Chooses Based On Which Confirms Existing Bias

A National Weather Service forecaster has selected the European Centre for Medium-Range Weather Forecasts model over the Global Forecast System model for his weekend forecast, a decision he attributes to the ECMWF's superior physics and that his colleagues attribute to the fact that the ECMWF agrees with what he already believed. Forecaster Kevin Ensemble, 38, was preparing the weekend forecast when the two leading global weather models diverged significantly in their handling of an approaching low-pressure system. The GFS predicted the system would track south, bringing rain to the region. The ECMWF predicted a more northerly track, keeping the area dry. "The Euro is handling the upper-level pattern better," Ensemble explained, using the informal name for the ECMWF that American meteorologists deploy to signal expertise. "The vorticity dynamics are more physically consistent in the European solution. I'm going with the Euro." Colleague Sarah Spaghetti, who was reviewing the same data, observed that Ensemble had mentioned on three separate occasions before looking at the models that he "felt like it would be a dry weekend." "He decided it would be dry at 7 a.m.," Spaghetti noted. "The models loaded at 8 a.m. He spent fifteen minutes finding the model that agreed with his 7 a.m. gut feeling and then explained why that model was scientifically superior. This is not how ensemble forecasting works." Ensemble rejected the characterization. "I've been forecasting this region for twelve years. My intuition is itself a model — a neural network trained on thousands of weather events. When my intuition and the ECMWF agree, that's ensemble convergence." "That's confirmation bias with meteorological vocabulary," Spaghetti replied. The weekend forecast was issued with dry conditions. The actual weather delivered 0.8 inches of rain, consistent with the GFS solution. Ensemble has attributed the miss to "an unusual deviation in the subtropical jet that no model handled well," a statement that Spaghetti has noted applies exclusively to the model he chose.