Hartmuth et al. (2026) Predictability of extreme surface weather associated with Mediterranean cyclones in ECMWF ensemble forecasts - Part 1: Method and case studies

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Identification

• Journal: Repository for Publications and Research Data (ETH Zurich)
• Year: 2026
• Date: 2026-01-16
• Authors: Katharina Hartmuth, Dominik Büeler, Heini Wernli
• DOI: 10.3929/ethz-c-000793792

Research Groups

Not explicitly stated, but implies involvement with or use of products from the European Centre for Medium-Range Weather Forecasts (ECMWF).

Short Summary

This study introduces a probabilistic, object-based method to quantify the predictability of extreme surface weather events (heavy precipitation, severe winds) linked to Mediterranean cyclones using operational ensemble forecasts, finding good predictability for lead times up to 48 hours but high variability thereafter, especially for smaller or less coherent events.

Objective

• To quantify the predictability of extreme surface weather conditions (heavy precipitation, severe winds) linked to Mediterranean cyclones using operational ensemble forecasts.

Study Configuration

• Spatial Scale: Mediterranean region, with extreme weather objects identified at grid points.
• Temporal Scale: Case studies between November 2022 and September 2023, with forecast lead times up to and exceeding 48 hours.

Methodology and Data

• Models used: Operational ensemble forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF).
• Data sources: Operational ensemble forecasts. Extreme surface weather objects are identified at grid points exceeding the seasonal 99th percentile of precipitation and surface wind parameters.

Main Results

• Mediterranean cyclones and their attributed extreme surface weather objects are predicted well for lead times less than or equal to 48 hours.
• For longer lead times, ensemble performance exhibits significant case-to-case variability.
• Predictions of extreme surface weather objects are found to be more uncertain under three conditions: (i) for smaller and less coherent objects, (ii) if the associated cyclone is captured by fewer ensemble members, and (iii) during the earlier stage of the cyclones' lifecycle.
• Three illustrative case studies (Storms Daniel, Denise, and Jan) occurring between November 2022 and September 2023 were analyzed.

Contributions

• Introduces a novel probabilistic, object-based method for attributing extreme surface weather events to Mediterranean cyclones.
• Provides a quantitative assessment of the predictability of these extreme events using operational ensemble forecasts.
• Establishes the methodological foundation for a multi-year investigation into the predictability of extreme weather linked to Mediterranean cyclones.

Funding

Not specified in the provided text.

Citation

@article{Hartmuth2026Predictability,
  author = {Hartmuth, Katharina and Büeler, Dominik and Wernli, Heini},
  title = {Predictability of extreme surface weather associated with Mediterranean cyclones in ECMWF ensemble forecasts - Part 1: Method and case studies},
  journal = {Repository for Publications and Research Data (ETH Zurich)},
  year = {2026},
  doi = {10.3929/ethz-c-000793792},
  url = {https://doi.org/10.3929/ethz-c-000793792}
}