The origins of Storm Ciaran: From diabatic Rossby wave to warm-seclusion cyclone with a sting jet

The evolution of Storm Ciar & aacute;n was different from what is commonly attributed to windstorms affecting northwest Europe. Ciar & aacute;n initially developed as a diabatic Rossby wave, driven by low-level latent heat release and with negligible upper tropospheric forcing. It then crossed the jet stream, intensifying explosively while developing a low-level warm seclusion and producing extreme near-surface winds, including sting jets. Ciar & aacute;n is an example of an extreme windstorm following this pathway and highlights the need of a systematic assessment of its relevance in our warming climate.