Severe storm signatures in three-dimensional lightning data (LMA): isolated lightning on the overshooting cloud tops

Lightning Mapping Array (LMA) networks are used to detect very high frequency (VHF, 60–66 MHz) electromagnetic sources associated with lightning channels inside clouds, providing three-dimensional lightning data. Over the past decades, LMA has been used in scientific campaigns with the aim of improving our understanding of electrification processes and revealing 3D lightning signatures related to severe weather. The use of real-time LMA data in weather surveillance and nowcasting provides valuable additional information to weather forecasters, playing an essential role in early warning alerts alongside other remote sensing systems such as traditional lightning detection networks, radar, and satellite. Since 2023, an operational LMA network has been running in real time in Catalonia (northeastern Iberian Peninsula) as a collaboration between the Meteorological Service of Catalonia (SMC) and the Technical University of Catalonia (UPC). The XCALMA (extended Catalonia LMA) network consists of 30 LMA stations, spanning from the coast to the Pyrenees to cover the entire 32,000 km² country, making it the largest LMA network in Europe. Several severe weather signatures can be detected using LMA data. One of them is the presence of isolated VHF detections in the overshooting top (OT), observed throughout the entire OT lifecycle. These detections, also known as sparkles, have been shown in some studies to precede surface severe weather reports—even occurring earlier than the commonly used lightning jump signature. In this study, we focus on the analysis of a selection of severe storms reported in Catalonia between 2023 and 2025 that exhibited this signature, including large-to-giant hail and tornadic events. We combine LMA data with C-band radar and satellite observations to evaluate the presence of lightning in the OT as a potential predictor of severe weather.