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https://doi.org/10.5194/egusphere-2025-4111
https://doi.org/10.5194/egusphere-2025-4111
29 Aug 2025
 | 29 Aug 2025

Quantifying forecast uncertainty of Mediterranean cyclone-related surface weather extremes in ECMWF ensemble forecasts. Part 1: Method and case studies

Katharina Hartmuth, Dominik Büeler, and Heini Wernli

Abstract. Extratropical cyclones are the main cause of high-impact weather events in the Mediterranean such as heavy precipitation, floods, severe winds, and dust storms. However, the accuracy in predicting the timing, location, and intensity of such events is often insufficient, which is typically related to errors in cyclone position, propagation, and intensity. In this two-part study we use operational forecasts from the ECMWF ensemble prediction system to quantify uncertainties in predicting high-impact weather conditions linked to Mediterranean cyclones. We apply an object-based approach to attribute Mediterranean cyclones to events of extreme precipitation and surface winds. In this first part, we introduce the probabilistic method and three illustrative case studies of Mediterranean cyclones that occurred between November 2022 and September 2023, including the infamous Storm Daniel as well as Storms Denise and Jan. We find that the cyclones as well as their attributed objects of extreme surface weather are predicted well for lead times ≤48 h. However, for longer lead times there is large case-to-case variability in the ensemble performance. Predictions of extreme surface weather objects are found to be more uncertain (i) for smaller and less coherent objects, (ii) if the attributed cyclone is captured by fewer ensemble members, and (iii) during the earlier stage of the cyclones' lifecycle.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Weather and Climate Dynamics.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Katharina Hartmuth, Dominik Büeler, and Heini Wernli

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Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-4111', Anonymous Referee #1, 11 Sep 2025
  • CC1: 'Comment on egusphere-2025-4111', Michael Schutte, 29 Sep 2025
  • RC2: 'Comment on egusphere-2025-4111', Anonymous Referee #2, 01 Oct 2025
  • RC3: 'Comment on egusphere-2025-4111', Anonymous Referee #3, 03 Oct 2025
Katharina Hartmuth, Dominik Büeler, and Heini Wernli
Katharina Hartmuth, Dominik Büeler, and Heini Wernli

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Short summary
This study presents three case studies of applying a newly developed method to quantify the uncertainty of the operational ECMWF ensemble in forecasting precipitation and wind extremes associated with Mediterranean cyclones. We find that the cyclones as well as their associated extremes are predicted well for lead times ≤48 h; however, for longer lead times there is large case-to-case variability in the ensemble performance.
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