Extratropical Cyclones
Extratropical cyclones are intense low-pressure systems responsible for much of the severe weather in the mid-latitudes, including extreme winds, heavy precipitation, and coastal flooding. Understanding how anthropogenic climate change alters their characteristics — intensity, track, and associated impacts — is critical for risk assessment and adaptation.
In Jiménez-Esteve et al. (2026) we develop a forecast-based attribution methodology using AI-based weather prediction models. By running forecasts under factual (present-day) and counterfactual (pre-industrial) climate conditions, we quantify the human influence on individual cyclone events before or as they unfold — providing near-real-time attribution at a fraction of the computational cost of traditional physics-based approaches.
The videos below show the evolution of two major extratropical cyclones simulated with FourCastNetv2, an AI-based weather model, under factual climate conditions, from two days before to two days after peak intensity.
Storm Ciarán — November 2023
One of the most intense extratropical cyclones to strike western Europe in decades, causing record wind gusts and widespread damage across France, Italy, and Switzerland.
Cyclone Claudia — November 2025
A powerful extratropical cyclone that struck the Iberian Peninsula and northwest Africa in November 2025, characterized by an intense atmospheric river that channelled vast amounts of moisture into the region, producing exceptional precipitation totals and strong winds.
Attribution of Precipitation Extremes
The figure below (Fig. 10 from Jiménez-Esteve et al. 2026) compares area-averaged precipitation forecasts from the AIFS model under factual (red, current climate) and counterfactual (blue, pre-industrial climate) conditions for both storms.
For Storm Ciarán, the factual forecast yields ~9% more precipitation than the counterfactual (30.7 vs 28.0 mm), with a highly significant difference (p = 2.9×10⁻⁵). For Cyclone Claudia, the factual forecast is ~6% wetter (32.2 vs 30.3 mm; p = 0.042). These results indicate that anthropogenic climate change substantially enhanced the precipitation associated with both storms, consistent with the thermodynamic argument that a warmer atmosphere holds more moisture.
