Strong updrafts occur in severe thunderstorms, causing the overshooting tops, an increase in the total lightning activity, and generating a frozen drops nucleus that will produce severe weather when it collapses. The Echo Top is a measurement of the vertical development of the cloud, considering a certain reflectivity threshold: the higher the threshold value, the lower the altitude reached. The present research shows the distribution of the Echo Tops of three reflectivity thresholds (12, 35, and 45 dBZ) in Catalonia for the period 2013–2021, comparing the distribution with the maps of hail, lightning jumps, and the topography of the region. The analysis shows how the maxima occurrence of Echo Tops varies depending on the threshold, indicating that thunderstorms have an initial development at 12 dBZ in the mountainous area, while the 35 and 45 dBZ maxima are shifted to the south, in regions with lower mountains. This last maximum is nearly coincident with the region more hit by large hail.

Previous studies in Catalonia (NE Iberian Peninsula) showed a direct relationship between the Lightning Jump (LJ) and severe weather, from the study of different events, occurring in the last few years in this region. This research goes a step beyond by studying the relationship between LJ and heavy rainfall, considering different criteria. It selects those episodes exceeding the 40 mm/h threshold, dividing them between those with or without LJ occurrence (3760 and 14,238 cases, respectively). The time and distance criteria (<150 km and <50 min, respectively) allow the detection of rainfall episodes with LJ, to establish an accurate relationship between the jump and the heavy rain occurrence. Then, lightning and radar data are analyzed, considering monthly and hourly distributions. Skill scores for the period 2013–2018 showed good results, especially in summer, with values of POD ≃ 90% and FAR ≃ 10%

Several works have shown that lightning jumps are precursors of severe weather in deep-convective thunderstorms. Since 2017, the Meteorological Service of Catalonia has operationally run an algorithm that identifies lightning jumps (LJs) in real time. It has resulted in being an effective tool for nowcasting severe weather with a lead time between 15 min and 120 min in advance. This time can be of high value for managing emergencies caused by severe phenomena or heavy rains. The present research focused on the events’ analysis in which more than one lightning jump occurred, searching for those elements that differentiate single warning cases. Thunderstorms producing LJs were divided into two main categories, depending on the number of jumps triggered during the life cycle. Besides, both classes were split into two main sub-types, based on the level of the LJ that occurred. Multiple LJ thunderstorms produce more Level 2—related to severe weather—jumps than Level 1—small hail or intense precipitation—while in the case of a single LJ, the opposite behaviour occurs. In general, multiple LJ thunderstorms with at least one Level 2 jump are the more intense and have a higher vertical development. Finally, lineal and well-organised thunderstorms are the more common modes in those intenser cases.

Hail events are common in Catalonia during the warm season (May to September), but especially between June and August. These cases produce important damages to agriculture and infrastructure. The campaign of 2022 will be remembered by three different phases: the first and last phases, which were very stable and with few events, and the middle phase, which had a large number of episodes. Some of the cases had an important social impact because of the large areas affected or the economical damages. The present analysis used the vertically integrated liquid radar product for estimating the hail swaths. Hail swaths are classified according to different parameters, allowing for the characterization of the campaign and a comparison with the period of 2013–2021. The results show how the month of June had a deficit of cases with respect to the reference period (half of the cases), July presented similar values, and August had a positive anomaly, with five times more cases. In addition, the first ever case of giant hail in Catalonia occurred in August 2022, a month with more than five times the number of cases of severe and very large hail with respect to the average of the period of 2013–2021.

The time and spatial variability of hail events limit the capability of diagnosing the occurrence and stones’ size in thunderstorms using weather radars. The bibliography presents multiple variables and methods with different pros and cons. The studied area, the Lleida Plain, is annually hit by different hailstorms, which have a high impact on the agricultural sector. A rectangular distributed hail pad network in this plain has worked operationally since 2000 to provide information regarding different aspects of hail impact. Since 2002, the Servei Meteorològic de Catalunya (SMC) has operated a single-pol C-band weather radar network that volumetrically covers the region of interest. During these years, the SMC staff has been working on improving the capability of detecting hail, adapting some parameters and searching for thresholds that help to identify the occurrence and size of the stones in thunderstorms. The current research analyzes a twenty-year period (2004–2023) to provide a good picture of the hailstorms occurring in the region of interest. The main research result is that VIL (Vertically Integrated Liquid) density is a better indicator for hailstone size than VIL, which presents more uncertainty in discriminating different hail categories.

Introduction: On 30 August 2022, a giant hail-bearing supercell hit Catalonia (NE Iberian Peninsula), producing stones 12 cm in diameter. This is the most severe episode ever recorded in the country. Seventy people were injured, resulting in one fatality; several buildings were severely damaged, which resulted in substantial financial losses (more than €6M).Methods: In the present study, we analyze the stones collected during fieldwork to gather information on their growth processes. This analysis was conducted considering two lines of investigation. In this paper we focus on the innovative and never-before-used technique of the Computed Tomography Scan, which was utilized to analyze hailstones and their interiors, the outcomes were groundbreaking. It makes it possible to obtain a complete 3D view of the interior of the stone, without producing any alteration in the structure. Through this technology, the different layer densities have been quantified. This is the main novelty of the study and opens a promising door to more analyses in this field.Results: The analysis has revealed some interesting results that help to verify previous theories. For instance, the nuclei can be placed far from the stone center, even if the hailstone is externally spherical.Discussion: Besides, a thicker hailstone layer in one direction indicates the falling direction. Finally, the different layer densities show growth process variations.