For many years the Met Office has verified its forecasts by comparing actual with forecast sea-level pressures and calculating a forecast error. The graph shows how many days into a forecast period this error is reached compared to a baseline in 1980. This graph shows that a three-day forecast today is more accurate than a one-day forecast in 1980.

These comparisons are based upon the 36-month root-mean-square errors of mean sea-level pressure forecasts over an area covering the North Atlantic, most of western Europe and north-eastern parts of North America. This area was chosen because of the long history of verification statistics going back many years to before the time the Met Office ran a global NWP model.