Seven days before Sandy made landfall in New Jersey, the atmospheric crystal ball was partly cloudy. The US National Weather Service forecast model showed a chance that Sandy might come ashore, but indicated that it was more likely the storm would spin off into the Atlantic. The European Centre for Medium-Range Weather Forecasts (ECMWF) model, however, definitely pointed the storm ashore. It would be about three days before the US model totally converged on the Europeans' forecast.
Essentially, the Europeans:
- have a bigger, better supercomputer...
- that specializes in medium-range predictions, and
- takes continuous data for half a day for their simulations;
As opposed to Americans who:
- have a less powerful computer
- that does short, medium, and long range predictions, and
- only take "snapshots" of initial conditions and have to run with that.
Ars Technica: Why European forecasters saw Sandy’s path first