R2O STORMS: Real-Time Ensemble Forecast Products For Extratropical Cyclones In Northern Europe

Modern numerical weather prediction systems produce unprecedented volumes of data up to hundreds of terabytes every day. While advances in computing capabilities have improved overall forecast skill, they also introduce technical challenges for forecasters. Transforming large amounts of complex ensemble data into useful information for rapidly evolving weather situations is difficult because forecasters have limited time to analyse all available data. Furthermore, raw model output is also difficult to interpret for the public, who often rely on a single forecast provided by their local weather provider. The European Center for Medium-Range Weather Forecasts (ECMWF) produces data from the physics-based Integrated Forecasting System (IFS), but recently they have also started to offer data-driven products from the Artificial Intelligence/Integrated Forecasting System (AIFS). ECMWF already offers products that track and quantify extratropical cyclones (ETC) through an ETC database (CDB) on their website, but for now this does not yet include AIFS data and mainly focuses on greater Europe and the North Atlantic region.

This project presents real-time ensemble forecast products designed to identify, track and quantify approaching ETCs affecting northern Europe using both IFS and AIFS data. The products are co-designed with operational forecasters at the Finnish Meteorological Institute (FMI) to ensure they meet the criteria for integration into operational use. Automated cyclone tracking software TRACK is applied to each forecast member to identify and quantify the impact-relevant metrics of approaching systems. Storms are assessed according to metrics ranging from traditional dynamical measures like maximum vorticity and minimum mean sea level pressure to impact-relevant metrics such as wind footprint and storm severity index, which offer more value for the user.

Ensemble data are condensed and presented as forecast products delivered on a publicly accessible website which updates in real-time. The forecasts are compared against climatology and previous high-impact storms, which places approaching systems into a historical context and helps inform how unusual and potentially impactful they are. The provided ensemble-based forecast products have not previously been implemented for ETCs in northern Europe. The project offers a novel method for monitoring and communicating the likelihood and severity of ETCs.