It was far too small a victory to count as an equalizer. But cheers were still heard in U.S. meteorological circles after the storm that hit the country's East Coast last month left the city of New York mostly unscathed. For more than two decades the Global Forecast System (GFS), the leading weather-prediction model produced in the United States, has been notably less accurate than its chief competitor, published by the European Centre for Medium-Range Weather Forecasts (ECMWF). Although this deficit went largely unnoticed for years, it was laid bare by Hurricane Sandy. A week before that storm's landfall in 2012, the ECMWF predicted it would veer toward the coast while the GFS showed it remaining at sea.
In response to this failure, Congress authorized $34 million of extra money to spend on forecasting. A new version of the GFS went into operation on Jan. 14, and two weeks later it passed with flying colors. On Jan. 25 the ECMWF predicted New York would, on Jan. 27, labor under 25 inches of snow brought by the storm. The GFS suggested 7 inches. That turned out to be far closer to the truth.
It is, however, too early for the Americans to celebrate. The GFS projection for the blizzard's western edge differed from the ECMWF's by 120 miles — a weather-forecasting hair's breadth. The only reason anyone noticed this discrepancy was that the gap happened to encompass the country's most populous city.
This episode, moreover, may have been a fluke. During its three weeks of operation, the new GFS remained outclassed. On a standard measure — predicting the altitude at which the atmospheric pressure is half as great as at sea level — it still trails the ECMWF model.
Nonetheless, the GFS' strong showing during January's nor'easter offers solace to critics who feared the United States would never catch up with Europe in matters meteorological. Weather forecasting is fiendishly complex, and improvements tend to arise not from great leaps forward but rather an accumulation of incremental advances.
The ECMWF's most obvious advantage has been in raw computing power. Its Cray XC30 supercomputer can perform up to 2 quadrillion calculations a second, about 10 times more than the GFS hardware before the recent upgrade. As a result, it carves up the Earth's atmosphere into svelte cells about 10 miles square and 137 layers deep, compared with roughly 17 miles and a mere 64 layers for the old GFS. The ECMWF's computing muscle also lets it start its projections with a replay of the past 12 hours of weather, using 40 million data points derived from observations collected by ground stations, airplanes, balloons and satellites. In contrast, the GFS begins with a snapshot of a single moment.
The ECMWF also deserves credit for deploying its computational force wisely. The center was a pioneer in using satellites to fill gaps in the data over the oceans, and in developing "ensemble forecasts" that generate a range of outcomes by employing slightly different starting conditions to produce multiple predictions. Its current model runs 52 such forecasts in parallel, each with a probability assigned to it.
Weather forecasters in America have full access to the ECMWF's model. However, the United States still has good reason not to free-ride on the Europeans' work. Private U.S. firms have to pay for it, and the ECMWF is unlikely to develop regional or local models focused specifically on the United States. Moreover, giving the ECMWF a worthy competitor would probably lead to better forecasts overall.
The new GFS has certainly narrowed the gap. Its resolution is now about 8 miles, though it still has only 64 layers. By November it is expected to run on a faster computer than the ECMWF's. It could be in line for further upgrades if the new, Republican Congress reintroduces the Weather Forecasting Improvement Act proposed last year — though the party's global-warming skeptics are likely to demand that much of the additional $120 million a year the bill offered be taken away from research on climate change.
According to Cliff Mass, a professor of meteorology at the University of Washington, more money will not be enough to catch up with the Europeans. The United States, he says, must integrate its separate research and forecasting divisions, and include more contributions from nongovernment experts. Compared with pushing through cultural change in large public bureaucracies, predicting the weather is easy.
Copyright 2013 The Economist Newspaper Limited, London. All Rights Reserved. Reprinted with permission.