Reanalysis and reforecast of three major European storms of the twentieth century using the ECMWF forecasting system. Part I: Analyses and deterministic forecasts

Abstract

In Part I of this study recent versions of the ECWMF Integrated Forecasting System (IFS) are used together with historical observational data to carry out reanalyses and deterministic reforecasts of three major north-west European wind storms of the twentieth century. The storms considered are the Dutch storm of 1 February 1953, the Hamburg storm of 17 February 1962, and the British October storm of 1987 (Great October Storm). Common to all these storms is their severity, which caused large loss of life and widespread damage. Reanalysis of the storms is based on a 3D-Var and 4D-Var assimilation scheme at a horizontal resolution of T L 159 (≈125 km) and T L 511 (≈50 km), respectively. Similarly, two different horizontal resolutions (T L 159 and T L 511) are used to investigate the deterministic predictability of these storms. The lower-resolution system is exactly that used in the ERA-40 reanalysis project. The high-resolution system is a more recent version of the ECMWF IFS.It is shown that the basic characteristics of the Dutch and Hamburg storms that gave rise to the storm surge are well predicted by the single deterministic forecasts up to about 48 and 84 hours, respectively, in advance.Our capability to predict the Great October Storm is more difficult to assess. On the one hand, even recent versions of the ECMWF IFS underestimate the severity of the storm in the very short-range (12-24-hour forecasts started at 12 UTC 15 October 1987). On the other hand, the high-resolution version of the ECMWF IFS provides excellent deterministic forecasts of the track and intensity of the storm up to 96 hours in advance. However, there are errors in the timing of the storm (12 hours for the 96 hour forecast).From the results presented in this study it is concluded -bearing in mind the limited number of cases considered -that with the current ECMWF forecasting system reliable deterministic predictions of some European wind storms are possible several days in advance.

The ERA‐40 re‐analysis

“…1958-66 1967-72 1973-78 1979-90 1991-2001 Northern hemisphere 94 95 94 93 96 Southern hemisphere 75 82 91 95 97 (a) Synoptic systems Reassurance as to the basic synoptic quality of the ERA-40 analyses for the extratropical northern hemisphere early in the period was provided by subjective comparison of synoptic maps from ERA-40 analyses and forecasts with published contemporary analyses, such as those for conditions at the time of the Windscale nuclear accident in October 1957 (Crabtree 1959) and the launch of the first meteorological satellite in April 1960 (Fritz and Wexler 1960). Jung et al (2004Jung et al ( , 2005 present specific examples for the devastating Hamburg storm of February 1962, and from an additional assimilation using the ERA-40 system for a period leading up to the even more destructive North Sea storm that occurred on the night of 31 January to 1 February 1953.…”

Sensitivity of extratropical cyclone characteristics to horizontal resolution in the ECMWF model

“…Moreover, they have large impacts on society, primarily due to their capability of producing severe weather events (e.g. Buizza and Hollingsworth 2002;Jung et al 2004).…”

Reanalysis and reforecast of three major European storms of the twentieth century using the ECMWF forecasting system. Part II: Ensemble forecasts

“…The target area is the Northern Hemisphere. The singular vectors were computed for the high-resolution analysis discussed in detail in Jung et al (2004). The initial conditions are further perturbed using evolved perturbations from two days earlier (Barkmeijer et al 1999).…”