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First ECMWF ensemble forecast, 24 November 1992

First ECMWF operational ensemble forecast

Black contours show the traditional single forecast for 500 hPa height made at 12 UTC on 24 November 1992 for a lead time of 4 days. It shows a low pressure system over the central North Atlantic and a ridge over western Europe.

Before the implementation of the ensemble, there was no indication of uncertainty in the forecast. The shading shows the first estimate of uncertainty, derived from the spread of the ensemble members. Light blue shading indicates regions where we could have confidence in the single forecast; dark blue regions indicate the potential for larger errors. Grey contours show the verifying analysis.

Indeed, the single forecast was quite accurate in the light blue regions, and less accurate in the dark blue regions, particularly in the vicinity of the Low. The ensemble, and the value derived from it, has improved greatly since this first forecast.



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