Session 12 | Collection of storm data, historical events, and damage assessments

Session 12

Collection of storm data, historical events, and damage assessments

Orals MO6

| Mon, 17 Nov, 16:45–17:45 (CET)|Room Hertz Zaal

Posters TH4

| Attendance Thu, 20 Nov, 14:30–16:00 (CET) | Display Wed, 19 Nov, 09:00–Thu, 20 Nov, 18:30|Poster area, P85–103

Orals: Mon, 17 Nov, 16:45–17:45 | Room Hertz Zaal

16:45–17:00

ECSS2025-192

Damage Surveying Methods for Canadian Severe Wind Events

Aaron Jaffe, Lesley Elliott, Connell Miller, and David Sills

Historically, tornadoes in Canada have been significantly underreported, primarily due to a low population density away from the southern border of the country. Since shortly after its inception in 2017, the Northern Tornadoes Project (NTP), now part of the Canadian Severe Storms Laboratory (CSSL), at Western University, has been the authority on the documentation and study of tornadoes and other damaging wind events caused by severe convective storms in Canada. Methodical and thorough documentation of these severe wind events has been crucial to the NTP and CSSL’s success. Since 2017, Canada averages over 100 recorded tornadoes per year, second most of any country in the world.

There are many ways that the NTP documents and analyzes severe wind events, including through radar data, satellite and aircraft aerial imagery, and social media reports. However, the most crucial elements of the analysis of notable severe wind events are the ground and remotely piloted aircraft (i.e. drone) damage surveys that are conducted on-site following these events. During the summer months in Canada that are prone to severe convective storms, the CSSL has three teams located across the country that are equipped to conduct damage surveys located in London, Ontario; Winnipeg, Manitoba; and Olds, Alberta. These teams are composed of CSSL staff, graduate students, and undergraduate interns. All members of the CSSL that make up the damage survey teams undergo rigorous training at the start of the summer, covering topics such as safety, documenting wind damage, drone flying, and interacting with homeowners. The NTP also creates severe weather outlooks prior to storms, and preliminary event maps of social media and other damage reports after damaging winds occur, to prepare and assist the field teams.

There is an abundance of preparation and effort to ensure that the NTP’s ground and drone damage surveys of severe wind events are conducted effectively and safely, while collecting high-quality data. This presentation will detail the NTP’s organization, preparation, and execution of these surveys, and how other research groups could implement similar tactics to survey severe wind damage in various regions of the world.

How to cite: Jaffe, A., Elliott, L., Miller, C., and Sills, D.: Damage Surveying Methods for Canadian Severe Wind Events, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-192, https://doi.org/10.5194/ecss2025-192, 2025.

17:00–17:15

ECSS2025-186

Automated Satellite Detection of Tornado Forest Damage in Canada

Daniel Butt, Lesley Elliot, David Sills, Gregory Kopp, and Mark Daley

The Northern Tornadoes Project (NTP), a division of the Canadian Severe Storms Laboratory (CSSL), has the goal of detecting every tornado that occurs in Canada. However, due to Canada’s vast area, often the only significant damage caused by a tornado occurs in remote forested regions that may go unreported. In order to detect these remote, unreported tornadoes, researchers at the NTP perform an end-of-season systematic sweep of Canada using satellite imagery. By comparing satellite imagery between different dates, large swaths of damaged trees can be detected and classified as tornado damage, among other severe storms (including downbursts).

Performing systematic sweeps of satellite imagery for all forested regions of Canada (over 4 million km²) is time-consuming, currently taking a team of researchers multiple months to complete. In order to speed up this process, an automated computer vision model is utilized. However, due to the rarity and diversity of tornado tracks, existing computer vision instance segmentation architectures may fail to achieve a high enough accuracy to detect every tornado in the vast search area. Instead of directly predicting tornadoes, this study develops a forest damage detection model that utilizes a convolutional neural network to automatically compare small sections of satellite imagery between different dates and identify regions that contain significant changes to the forest. Resultingly, only areas with detected forest damage need to be manually searched for tornado tracks, substantially speeding up the required search time, while being reliable enough to ensure no tornado is misclassified. Future work will aim to utilize this model outside of Canada in the similar forested regions of Northern and Eastern Europe.

How to cite: Butt, D., Elliot, L., Sills, D., Kopp, G., and Daley, M.: Automated Satellite Detection of Tornado Forest Damage in Canada, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-186, https://doi.org/10.5194/ecss2025-186, 2025.

17:15–17:30

ECSS2025-273

Radar Determined Intense Tornado Frequencies, Wind Profiles and the BEST Tornado Study

Joshua Wurman and Karen Kosiba

Since 1995, DOWs have observed over 30 very intense tornadoes, with wind speeds calculated to exceed 200 mph (89 m/s), exceeding the EF-5 minimum wind speed. Some of these have been associated with officially-rated EF-5 levels of damage, but most have not.

We will discuss the spectrum of tornado structures, sizes, propagation speeds, and wind speed durations of these most intense tornadoes, how these relate to documented damage and resulting ratings. We will examine intense 2024 tornadoes, with a particular focus on measurements of a tornado which crossed Greenfield, Iowa. This tornado was very small, with the region containing the most intense winds extending perhaps 200 feet, and propagating very rapidly, over 50 mph, resulting in a rapidly moving very small region of winds near 300 mph, well in excess of the minimum EF-5 (or old F-5) wind speed criterion. EF-4 damage was documented. This tornado also destroyed several wind power turbines, and DOW measurements will be examined at those locations. Factors affecting how observed and calculated wind speeds result in documented damage, including vertical dependences of wind speeds, especially in built-up areas with many structural and arboreal obstructions, methodology, tornado propagation speeds, tornado structure, and, of course, the availability of strong structures to be damaged, will be discussed.

We will present results in the context of the BEST tornado study and extended DOW radar based tornado wind speed climatologies.

How to cite: Wurman, J. and Kosiba, K.: Radar Determined Intense Tornado Frequencies, Wind Profiles and the BEST Tornado Study , 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-273, https://doi.org/10.5194/ecss2025-273, 2025.

17:30–17:45

ECSS2025-172

A reconstruction of 1 August 1674 thunderstorms over the Low Countries

Gerard van der Schrier and Rob Groenland

On 1 August 1674 an active cold front moved over the Low Countries. The accompanying thunderstorms along the squall line were abnormally active, leading to large-scale damage in Europe, from northern France to the northern parts of Holland where damages were particularly severe. The damages included destroyed bridges, like in Antwerp, to numerous churches, churchtowers and other buildings and ships lost in the harbour or at sea. The city of Utrecht was hit hardest by this event resulting in widespread damages that are still recognizable in the city landscape. Using reported and pictured observations of damages and modern meteorological concepts, the reconstruction of the storm points to an exceptionally severe squall line. The orientation and the velocity of the squall line are reconstructed and shows a developed bow-echo structure. An estimate of the strength of the strongest wind gusts is ≈ 55–90 m s−1 and is based on an assessment of the damages caused by this event. A rough estimate of the return time of this event, based on observed hail size, is between 1000 and 10,000 years.

The view in this presentation disagrees with the common perception that the damages are caused by a single tornado and the arguments for this novel view will be presented. However, there is evidence of embedded vortices in the damages to the city of Utrecht. These observations are discussed in the presentation.

How to cite: van der Schrier, G. and Groenland, R.: A reconstruction of 1 August 1674 thunderstorms over the Low Countries, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-172, https://doi.org/10.5194/ecss2025-172, 2025.

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Posters: Thu, 20 Nov, 14:30–16:00 | Poster area

Display time: Wed, 19 Nov, 09:00–Thu, 20 Nov, 18:30

P85

ECSS2025-7

Reconstruction of Meteorological Environment Leading to the Deadliest Polish Severe Weather Outbreak of July 4th 1928, Using Archival Data and 20th Century Reanalysis

Filip Skop

On July 4th 1928, one of the most impactful severe weather events in Polish history formed ahead of an advancing cold atmospheric front, causing over 60 fatalities, hundreds of injuries and massive destruction over large part of the country. Dozens of highly populated European cities, including Berlin, Poznań, Warsaw and Katowice, as well as hundreds of smaller towns and villages were significantly affected during the day. Most of the damage and human casualties were caused by hurricane force wind associated with thunderstorm's downdrafts. At least one tornado is suspected to have occurred and other damaging weather phenomena, such as large hail, dust storms and lightning induced wildfires were also reported. In order to recreate the weather environment leading to the "birth" of such an intense storm, ensembles of NOAA-CIRES-DOE Twentieth Century Reanalysis (20CR) were utilized and compared with archival data from Polish and German meteorological stations operating at that time. Dozens of press reports, covering the disaster and it's consequences, were gathered from Polish digital libraries' datasets to fully understand the timeline, scale and characteristics of this highly unusual and catastrophic weather event. The overall purpose of the research is to find comparisons between this historic case and recent severe weather outbreaks, assess the reliability of historical reanalyses in representation of mesoscale phenomena and to perform a high-resolution simulation using WRF-ARW model, based on downscaled versions of the most representative ensmbles of the reanalysis.

How to cite: Skop, F.: Reconstruction of Meteorological Environment Leading to the Deadliest Polish Severe Weather Outbreak of July 4th 1928, Using Archival Data and 20th Century Reanalysis, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-7, https://doi.org/10.5194/ecss2025-7, 2025.

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P86

ECSS2025-18

Uncovering Europe's Largest Hailstones: A cross-national hail size comparison using ESWD reports

Hendrik Feige

Every year, intense hailstorms leave behind a trail of damage across Europe, with some storms producing hailstones of extraordinary size. While national weather services collect hail reports—often supported by photos or eye witness accounts—there is currently a lack of a unified framework for comparing these extreme events across countries and over time. This investigation presents the first systematic ranking of the largest hailstones ever documented in European countries, based on verified reports and reliable historical sources.

By compiling and analyzing ESWD reports, I provide a valuable reference for meteorologists, enabling more accurate classification of future large-hail events. In addition, this initiative serves as a call to action for weather enthusiasts, historians, and the general public to contribute overlooked or forgotten hail reports from the past, potentially rewriting parts of Europe's severe weather history.

This poster presentation will point the attention to surprising records of lesser-known hail events, challenges in validating historical data, and the potential of citizen science for hail documentation. Our aim is to encourage greater collaboration between meteorological networks, stimulate public curiosity and highlight the importance of volunteer work in weather observation. Special thanks go to Thomas Schreiner (ESWD User Support) and Thilo Kühne (ESWD Quality Control Manager) for their support during this study.

How to cite: Feige, H.: Uncovering Europe's Largest Hailstones: A cross-national hail size comparison using ESWD reports, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-18, https://doi.org/10.5194/ecss2025-18, 2025.

P87

ECSS2025-21

Human Weather- and Impact-Reports in Austria – A Crucial Support to Mitigate Extreme Weather and Climate Impacts?

Thomas Krennert

Governments and civil authorities face increasing socio-economic challenges due to extreme weather and climate impacts. Effective decision-making requires robust data on weather- and climate-related hazards and damages, both for immediate warnings and long-term threat assessment.

Weather stations cannot detect hazards like flooding or wind damage, making observations from voluntary observers a valuable "ground truth" data source. This establishes a real-time feedback loop between weather warnings and impact reports, a critical capability for the national weather service GeoSphere Austria (formerly ZAMG) as a key advisor within Austria's National Crisis and Disaster Management (SKKM).

Since 2020, GeoSphere Austria has compiled a national database with nearly 160,000 human weather and impact reports via the web-app wettermelden.at. The app's parameters align with the European Weather Observer App (EWOB) from the European Severe Storms Laboratory (ESSL), enabling standardized, real-time exchange of impact reports between national and European levels via API. The API further allows external partners to interact with the GeoSphere database from their platforms, by their own communities, without the need of using extrinsic platforms, enhancing data integration. These reports also contribute to forensic damage assessments and climate impact research.

Most observers are weather enthusiasts, spotters, storm chasers, ham radio operators, students, and other motivated volunteers. Within the Trusted Spotter Network Austria (TSN) they are offered comprehensive training and regular workshops, facilitating knowledge exchange between citizen scientists and professionals. This program enhances the accuracy and reliability of reports from fully trained "Trusted Spotters."

GeoSphere collaborates with other European National Weather Services to exchange standardized human impact reports during cross-border extreme weather events, serving both warning purposes and scientific research.

GeoSphere maintains a growing network of partners and offers an extensive educational program for schools through the "Wetter-Partner-Schule" initiative, including Citizen Science Awards, webinars, workshops, and scientific information on weather forecasting, hazards, and the climate crisis. For example, Agricultural-Vocational Schools have integrated wettermelden.at into their daily routines.

The Austrian citizen science program wettermelden.at and the Trusted Spotter Network have been recognized for best practices by the European Meteorological Society (EMS) and the World Meteorological Organization (WMO).

How to cite: Krennert, T.: Human Weather- and Impact-Reports in Austria – A Crucial Support to Mitigate Extreme Weather and Climate Impacts?, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-21, https://doi.org/10.5194/ecss2025-21, 2025.

P88

ECSS2025-32

Reconstructing the 2022 France Hail Events: A Footprint at the Intersection of Science and Insurance

Harsh Mistry, Caroline McMullan, and Shane Latchman

Hailstorms represent a significant weather-related threats to the French insurance industry, as evidenced by the destructive 2022 hail season, which caused insured losses of approximately EUR 5 billion (FA, 2024). Two major outbreaks, linked to low-pressure systems Maya (early June) and Qiara (mid to late June), alone accounted for an estimated EUR 4.5 billion in property and automobile losses. This event ranks among the costliest hailstorms in French history and has reinforced the need for better understanding of hail severity and its impact on insurance portfolios. Given the heterogeneous and localised nature of this peril, accurately capturing hazard intensity and its spatial distribution remains a key challenge in catastrophe modelling.

Traditionally, hailstone diameter reports from the European Severe Weather Database (ESWD) have been used to characterize hail intensity. While valuable, these observations present several limitations when attempting to characterize hail footprints for a catastrophe model. One significant concern is the population bias, as hail reports tend to cluster in more densely populated regions, leading to incomplete and spatially uneven representation of the event footprint (Púčik et al., 2019). Furthermore, maximum hailstone diameter—commonly used as a proxy for severity—reflects only isolated peak values and fails to represent impact from full distribution of hail sizes across a region (Allen et al., 2015). From an insurance perspective, understanding the overall impact to the built environment is more relevant than just the largest hailstone observed. Additionally, hail mainly impacts the roofs of the structure, but wind-driven hail can pose a significant threat to windows and building cladding. Therefore, at Verisk we leverage range of datasets including radar reflectivity, hail observations and client claims data to develop a historical hail footprint that uses total impact energy as the intensity measure, which captures the observed damage patterns more realistically. This study outlines the approach used for developing the 2022 French hail event footprints and discusses several challenges encountered during this process. We also show how well these footprints captures the spatial severity of the event, thereby, enabling our clients to study their claims experience and increase their confidence in understand the hail risk.

How to cite: Mistry, H., McMullan, C., and Latchman, S.: Reconstructing the 2022 France Hail Events: A Footprint at the Intersection of Science and Insurance , 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-32, https://doi.org/10.5194/ecss2025-32, 2025.

P89

ECSS2025-51

Estimation of the damage linked to clusters of storms; a case study over the French insurer Generali

Laura Hasbini, Pascal Yiou, and Perringaux Arthur

Storms represent a significant natural hazard, particularly when they occur in rapid succession. In this study, we define storm clusters as sequences of multiple storms occurring within a short temporal window and over a limited spatial extent. Using a Lagrangian framework based on storm tracks, we identify clusters with a 96-hour time window, aligning with common reinsurance contract specifications. The example of storms Lothar and Martin, which struck France successively within 36h in December 1999, illustrates the severe consequences of clustering. Together, they remain the costliest storm-related event recorded in France, with an estimated loss of €6.8 billion [FFA, 2000].

To assess the broader relevance of such events, we analyze the historical loss records of Generali, a major Italian insurance company holding approximately 4% of the French market share. The loss dataset spans from 1998 to 2024. To disentangle overlapping impacts of consecutive storms, we implement a method that associates insured losses with specific storm tracks. Our analysis reveals that approximately 85% of historical storm-related losses are linked to storm clusters, underscoring the amplified risk posed by such sequences.

We then evaluate how clustering affects damage estimation. Traditional vulnerability curves are shown to underestimate losses when storms occur in clusters. We propose new vulnerability curves conditioned on compounded storm events. These improved curves should better capture the nonlinear accumulation of damage and highlight the need for cluster-aware risk models in insurance and reinsurance frameworks.

How to cite: Hasbini, L., Yiou, P., and Arthur, P.: Estimation of the damage linked to clusters of storms; a case study over the French insurer Generali, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-51, https://doi.org/10.5194/ecss2025-51, 2025.

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P90

ECSS2025-55

The DOWNBURST MXO: a real-time downburst monitoring service in eastern Spain

Cesar Azorin-Molina, Francisco Granell, Jose Gomez-Reyes, Carlos Calvo-Sancho, Andrés Barrio-Martín, Nuria P. Plaza-Martín, Andreas F. Prein, Sergio M. Vicente-Serrano, Luis Gimeno, Raquel Nieto, Deliang Chen, Tim R. McVicar, Zhenzhong Zeng, Amir Pirooz, Marcos Martínez-Roig, Juan Jesús González-Alemán, and María Luisa Martín

In the framework of the DOWNBURST project, here we present the first real-time downburst monitoring service in eastern Spain. Downbursts are strong winds that descend from a thunderstorm and spread out quickly once they hit the ground. These extreme winds are one of the most damaging natural events and can reach the force and produce damages similar to tornados. Downbursts are challenging to detect because of their sudden onset, isolated and short-lived behaviour.

The DOWNBURST MXO is a monitoring service based on the Valencian Meteorological Society (AVAMET), a distinctive network of weather stations in eastern Spain featuring extensive spatial coverage (over 750 stations) and high temporal resolution (10-minute intervals, with 3-second wind gust measurements), all while maintaining high data quality by citizen science weather observers. The service operates using an algorithm that continuously reads 10-minute data and automatically identifies whether a downburst is occurring based on sudden changes in reference variables such as strong winds accompanied by changes in air temperature, humidity, precipitation, and/or atmospheric pressure. Where established criteria are fulfilled, the Downburst MXO web application marks the location with a symbol that alarms the public about the occurrence of a downburst. In addition, the monitoring service alerts the station owner, allowing them to verify the event. The service also collects different data about downburst events, such as the location (coordinates), time, duration, impacts (tree falls, damages in structures, etc.) and, in future updates, about the type (microbursts, macrobursts; wet and dry downbursts; and heatbursts). Along with the automated data collection, the web-based app incorporates many key data-gathering functions such as uploading images (pictures and movies), audio and a description of the event. Each recorded event is in turn verified by the DOWNBURST project research team and becomes part of a downburst database.

In a warming climate, these straight-line winds are expected to increase in intensity and frequency. Consequently, this real-time downburst monitoring service provides alerts for areas experiencing downbursts and early-warnings to vicinity areas.

How to cite: Azorin-Molina, C., Granell, F., Gomez-Reyes, J., Calvo-Sancho, C., Barrio-Martín, A., Plaza-Martín, N. P., Prein, A. F., Vicente-Serrano, S. M., Gimeno, L., Nieto, R., Chen, D., McVicar, T. R., Zeng, Z., Pirooz, A., Martínez-Roig, M., González-Alemán, J. J., and Martín, M. L.: The DOWNBURST MXO: a real-time downburst monitoring service in eastern Spain, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-55, https://doi.org/10.5194/ecss2025-55, 2025.

P91

ECSS2025-63

Severe wind damage in the city of Córdoba, Spain, on March 9, 2024 linked to a possible misocyclone embedded within a cold front

Delia Gutiérrez Rubio and Juan de Dios Soriano Romero

On the night of March 8-9, 2024, a cold front associated with a powerful storm named Monica caused widespread rainfall and moderate to strong southwesterly winds in the south of the Iberian Peninsula. The city of Córdoba experienced significant wind damage, with many sources attributing it to a tornado. Further damage was reported at a solar thermal power plant in Posadas, located 25 km southwest of Córdoba.

In a High Shear Low Cape (HSLC) convective environment, remote sensing images show an enhanced convective line with undulations within it that suggest the possible existence of misocyclones —vortices on a scale between mesocyclones and tornadoes. This pattern, sometimes seen in narrow precipitation bands on cold fronts, has been linked in various studies with the formation of wind maxima and, occasionally, tornadoes in the northern side of these vortices, particularly when coinciding with breaks in the reflectivity pattern.

Damage assesment conducted by the authors revealed two parallel paths of destruction, both running from southwest to northeast. The maximum wind intensity was estimated to have reached category IF2 (International Fujita scale), implying maximum winds around 220 km/h.

We will present a brief analysis of the meteorological situation and remote sensing products, along with a summary of the field study carried out by the authors to conclude that, while the linear nature of the damage paths initially suggests two distinct tornadic phenomena, the proximity and likely simultaneous occurrence of these two parallel trajectories support an alternative hypothesis: both trajectories may have been associated with a single, somewhat larger vortex, a misocyclone. The damage path located further south could have been caused by downdraft winds on the southern flank of this misocyclone, while the northern path could have resulted from the formation of a small tornado on its northern flank.

How to cite: Gutiérrez Rubio, D. and Soriano Romero, J. D. D.: Severe wind damage in the city of Córdoba, Spain, on March 9, 2024 linked to a possible misocyclone embedded within a cold front, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-63, https://doi.org/10.5194/ecss2025-63, 2025.

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P92

ECSS2025-71

A tornado in Utrecht?

Kathrin Wapler and Marcus Beyer

While the knowledge of the synoptic and mesoscale conditions which provide an environment for the development of severe convective events are crucial for forecasting such events, statistical analysis are helpful to raise a general awareness of the possibility of severe convective events. Such analyses was recently performed for Germany based on the European Severe Weather Database (ESWD). The objective of the ESWD is to collect and provide information on severe convective storm events over Europe. In total approx. 22 000 tornado reports are listed in the ESWD. Approx. 14 500 are confirmed reports since 2000.

How likely are tornadoes at a specific location? Using Utrecht – the hosting city of the European Conference on Severe Storms 2025 - as an example, the awareness of the possibility of tornadoes at a specific location is addressed.

The topic will be presented as poster in a way to allow the conference participants to actively contribute by sharing and testing their knowledge of tornado occurrence. Do the participants correctly guess whether tornadoes were observed in the surroundings of Utrecht in the past? Do the participants know how often tornadoes occur in their country of residence? How close to their home was a significant tornado observed in the past?

How to cite: Wapler, K. and Beyer, M.: A tornado in Utrecht? , 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-71, https://doi.org/10.5194/ecss2025-71, 2025.

P93

ECSS2025-83

Simultaneous assessment of debris trajectories to determine characteristics of the July 1, 2023 Didsbury, Alberta, Canada EF4 tornado

Connell Miller, Collin Town, Daniel Butt, David Sills, and Gregory Kopp

The Enhanced Fujita scale is a useful assessment tool to determine wind speeds in tornadoes in Canada, the United States of America, and Japan. However, it is a damage-based assessment which relies on the tornado hitting damage indicators whose wind loads have been well-documented and researched (such as houses, mobile homes, and trees). Additionally, the Enhanced Fujita scale is unable to determine any additional characteristics of the tornado such as the ratio of wind speeds (swirl ratio), or the dimension of the core radius.

In a previous study, the authors of this abstract developed a forensic tool to analyse the trajectories of large compact objects (vehicles, farming equipment, trailers, haybales, etc) identified during damage surveys. By combining analytical tornado wind field models with debris equations, the lofting wind speeds required to recreate these observed trajectories can be estimated. This was achieved by utilizing a Monte Carlo simulation to randomly select parameters and plotting cumulative distribution functions to depict the likelihood of lofting at various wind speeds. Analyzing debris trajectories from several documented tornadoes in Canada revealed that this method yields threshold lofting wind speeds comparable to those estimated by other approaches. However, incorporating trajectories resulted in higher estimated lofting wind speeds than the EF-scale ratings derived from ground survey assessments based on structural damage.

All of the debris trajectories examined in the previous study were analysed as single independent instances. For example, in the EF4 Didsbury, AB tornado, although the focus was on a single combine harvester, there were multiple other large compact objects in the same area that were not analysed in the study. Additionally, the effect of the relative location of the object to the centre of the tornado was not considered.

The goal of this paper is to continue the development of a forensic tool for debris trajectories of large compact objects by analyzing the trajectories of multiple debris objects simultaneously. Analyzing multiple debris simultaneously narrows the range of possible tornadic parameters, which provides more insight to the characteristics of a tornado. Data from the EF4 Didsbury, AB tornado are applied as a case study to test this forensic tool.

How to cite: Miller, C., Town, C., Butt, D., Sills, D., and Kopp, G.: Simultaneous assessment of debris trajectories to determine characteristics of the July 1, 2023 Didsbury, Alberta, Canada EF4 tornado, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-83, https://doi.org/10.5194/ecss2025-83, 2025.

P95

ECSS2025-107

Assessing tornadoes and downbursts in Catalonia: field surveys and operational insights

Oriol Rodriguez, Santi Segalà, Nicolau Pineda, Ferran Fabró, and Roger Vendrell

Catalonia (32,000 km², northeast of the Iberian Peninsula) is affected every year by 5-10 severe convective damaging winds events (e.g., tornadoes, downbursts, or straight-line winds), posing risks to people, property, and public infrastructure. Although such events can occur throughout the country, they are most frequently observed in the coastal and pre-coastal areas, where the metropolitan areas of Barcelona and Tarragona are located.

Since 2020, the Meteorological Service of Catalonia (SMC) has systematically conducted in-situ damage surveys following reports of convective wind events. The objectives of these surveys are to (i) identify the phenomenon type, (ii) estimate the intensity using the International Fujita scale, and (iii) delimit the affected area. Over this five-year period, 11 reports have been published, encompassing 16 fieldworks. The Spanish public reinsurance company (Consorcio de Compensación de Seguros, CCS) has paid €2.6 million in compensation for damages caused by the analysed events.

The findings from these field surveys contribute to the development of a climatology of severe weather events, support the validation of severe weather early warning systems, and serve other scientific purposes including case studies. Furthermore, the reports are considered by insurance companies and the CCS, given that tornado damage is always covered by insurance in Spain, whereas other wind-related damage is only covered if wind speeds exceed specific thresholds. The information is also disseminated by the media due to its public relevance.

This work presents the SMC’s procedure for responding to severe convective wind events and its experience in surface-based damage assessment acquired over recent years. It also describes the incorporation of drones as a complementary tool, in collaboration with the Catalan Rural Agents Corps—an environmental law enforcement agency similar to forest rangers in other countries—which provides valuable support in obtaining a general overview and detailed damage information, especially in forested areas and complex terrain.

How to cite: Rodriguez, O., Segalà, S., Pineda, N., Fabró, F., and Vendrell, R.: Assessing tornadoes and downbursts in Catalonia: field surveys and operational insights, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-107, https://doi.org/10.5194/ecss2025-107, 2025.

P96

ECSS2025-128

Contribution of personal weather stations for observing deep-convection features near the surface

Marc Mandement and Alan Demortier

When thunderstorms develop in the atmosphere, they cause changes in temperature, relative humidity, pressure, wind and precipitation near the surface that can be detected by weather stations. However, standard weather station networks, which are maintained by national meteorological and hydrological services, cannot observe all of these variations, particularly those whose characteristic scale is smaller than the meso-γ-scale (2-20 km). One opportunistic solution for obtaining spatially denser observations comes from citizen science. Advances in wireless communication networks allow an increasing number of objects to be connected to the Internet (IoT for Internet of Things). These objects include personal weather stations, also known as citizen weather stations. In mainland France, the number of active personal weather stations providing real-time observations exceeded that of standard weather stations by a factor of approximately 40 in 2020.

Although there are many personal weather stations, the quality of their observations varies greatly due to the variable quality of their physical sensors, their highly heterogeneous installation environments, and their maintenance, among other reasons. This usually limits the use of this data unless it is coupled with strict quality control. Several fully automatic quality control algorithms have been developed in the scientific literature. One such example is the Mandement and Caumont (2020) algorithm, whose general principle is to statistically check surface pressure, temperature, and relative humidity observations against those from neighbouring standard weather stations, in such a way as to retain as much as possible the sudden variations caused by deep convection.

This algorithm has been adapted for real-time use, and the quality-controlled observations it produces are used in high-frequency meteorological analyses of temperature, relative humidity, and mean sea level pressure, over France. Case studies in which fine-scale structures appear in these analyses but are either partly or completely absent from analyses that only include observations from standard weather stations, will be presented. These fine-scale structures include temperature drops, humidity rise and mean sea level pressure jumps that accompany squall lines or individual convective cells, as well as oscillations that are associated with gravity waves triggered by deep convection. Initiatives launched at a European level to concentrate and share personal weather station observations will also be presented.

How to cite: Mandement, M. and Demortier, A.: Contribution of personal weather stations for observing deep-convection features near the surface, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-128, https://doi.org/10.5194/ecss2025-128, 2025.

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P97

ECSS2025-129

Ingredient-Based Analysis and Simulation of Violent European F4/F5 Tornadoes between 1965 and 1971

Jerome Schyns, Lisa Schielicke, and Christoph Gatzen

Between 1965 and 1971, Europe experienced an unusually high number of violent tornadoes, including six confirmed F4 events in Switzerland, France (2), Italy (2), and Germany, as well as one F5 tornado in France. This exceptional cluster of events provides a unique opportunity to investigate the synoptic and environmental conditions associated with high-end tornadoes in Europe.

Using data from the European Severe Weather Database (ESWD), ERA5 reanalysis, and historical surface and upper-air weather maps, we analyze the synoptic and mesoscale patterns associated with these tornadoes. Particular attention is given to large-scale synoptic processes such as the jet stream positioning, the presence of synoptic and mesoscale boundaries (such as cold fronts, drylines, and prefrontal convergence zones), and the strength of large-scale forcing.

Our analysis follows an ingredients-based approach focusing on thermodynamic and kinematic conditions, including the spatial alignment of low-level moisture, lapse-rates, lifting mechanism, and vertical wind shear. We find that many of these tornado events occurred under a favorable combination of strong low-level wind shear and enhanced CAPE, often within confined regions (”sweet spots”) of overlapping ingredients. A recurring pattern emerges, characterized by the presence of strong low-level streamwise vorticity and low lifted condensation levels (LCLs), which likely contributed to efficient storm organization and tornadogenesis by limiting evaporative cooling and thus cold pool strength.

ERA5 vertical profiles near the convective developments reveal consistent signatures of storm-favorable environments, including strong streamwise vorticity in the lowest kilometers, as well as low LCL heights indicative of surface-based convection with limited downdraft cooling. These findings are further supported by proximity soundings used to initialize idealized supercell simulations in Cloud Model 1 (CM1). Simulated storms develop robust mesocyclones, exhibit realistic storm motion vectors, and confirm the sensitivity of storm structure to variations in cold pool intensity and vertical shear.

Overall, the study suggests that the violent tornadoes of this period were not purely coincidental, but rather the result of rare yet repeatedly favorable synoptic and mesoscale configurations. These insights contribute to a better understanding of the environmental conditions supporting violent tornadoes in Europe and may aid in refining future risk assessments and forecasting strategies.

How to cite: Schyns, J., Schielicke, L., and Gatzen, C.: Ingredient-Based Analysis and Simulation of Violent European F4/F5 Tornadoes between 1965 and 1971, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-129, https://doi.org/10.5194/ecss2025-129, 2025.

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P98

ECSS2025-165

Reconstructing Thunderstorm Wind Speed Time Histories Using Forensic Damage Analysis

(withdrawn)

Djordje Romanic

P99

ECSS2025-166

Flash flood event in South Sardinia on 26-27 October 2024: preliminary case study and historic comparison

Pier Luigi Trudu, Lorenzo Smorlesi, and Alessandro Delitala

Between the late evening of October 26^th and the morning of October 27^th 2024, Sardinia was affected by intense and locally persistent thunderstorms that caused numerous critical issues across the territory, including flooding in residential areas, landslides, and the overflowing of small watercourses. The overall economic losses were estimated around 6.5M€.

During the night between the 26^th to 27^th October, a surface cold front approached Sardinia, and its eastward progression was decelerated by the blocking action of an anticyclonic ridge over the Balkans. This dynamic fostered the development of a low-level convergence line between the moist southeasterly flow entering the Gulf of Cagliari and drier air advected from the west. This convergence acted as the primary trigger for deep convection, and the persistent synoptic setup contributed to the quasi-stationary nature of the thunderstorms that subsequently formed over the Campidano plain.

The Decimomannu (Cagliari, CA) radiosounding at 00:00 UTC on October 27^th revealed a highly moist and unstable atmospheric profile with Mixed-Layer Convective Available Potential Energy (MLCAPE) values exceeding 2000 J/kg, negligible Convective Inhibition, and a Level of Free Convection (LFC) below 400 m.

In the whole event excessive rainfalls were measured by two close rain gauges: i) Vallermosa: hourly cumulative rainfall up to 60 mm, with a total event accumulation of 292.0 mm, most of it in 6 hours (mean climatic values are of 54.4 mm for October and 555.8 mm annually); ii) Siliqua: total cumulative rainfall of 409.6 mm over 48 hours from October 26^th to 27^th (compared to mean climatic values: 539.9 mm annually; 57.8 mm in October).

The analyzed flood event shares similarities with other significant precipitation events that have occurred in Sardinia over the past century. Given the significant impact each such event has had on the territory, it is considered particularly hazardous and warrants further in-depth study. The Meteoclimatic Department of ARPA Sardegna has initiated research activities to improve the prediction and prevention of this type of events.

How to cite: Trudu, P. L., Smorlesi, L., and Delitala, A.: Flash flood event in South Sardinia on 26-27 October 2024: preliminary case study and historic comparison, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-166, https://doi.org/10.5194/ecss2025-166, 2025.

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P100

ECSS2025-169

Unique observations of a back-building MCS in the arid Kalahari region of South Africa

(withdrawn)

Lynette Van Schalkwyk, Chris Reason, Ross Blamey, Callum Munday, and Richard Washington

P101

ECSS2025-243

Proposed Conceptual Framework for an International Hailstorm Intensity Scale

Simon Eng, Julian Brimelow, and Gregory Kopp

We propose a framework for the development and refinement of an internationally applicable hailstorm intensity scale that supports an objective, categorical characterisation of hailstorm intensity and damage potential. The intent is to develop a scale that is universally applicable across time and space. It should demonstrate utility for assessing historical events through to future projected changes in hailstorm intensity, as well as being applicable internationally for damaging hailstorms, regardless of location of occurrence or regional asset sensitivities.

The scale would need to address the many uncertainties associated with hail damage potential. These can be due to variability in hailstorm and hailstone characteristics (e.g., concurrent winds; hailstone hardness; hailfall density, size distribution and duration) which, in varied combination, may result in similar damage potential. These uncertainties can also stem from differences in asset response to hail impacts. The damage scale would need to allow for differences in the fragility and failure modes of key assets (i.e., agricultural crops, building surfaces and vehicles). Failure modes, for example, can fall on a spectrum encompassing brittle failure – with damage triggered by a peak or maximum kinetic energy (MKE) – while other damage receivers are better characterized by cumulative impact (accumulated kinetic energy, or AKE) and/or ductile failure (i.e., cumulative deformation) modes.

Data and information used to categorise storms should be “physically based” (i.e., tied/linked to event damage potential) but with uncertainties associated with those relationships also taken into account. Such a scale should be effective at easily communicating nuances and variability in the damage potential of hail events while not being unnecessarily complex.

By defining, a priori, the intended applications of such a scale, along with key performance indicators (i.e., metrics to determine if it meets intended scope and applications), the potential for successful development is increased. For example, a focus on intensity precludes a need for incorporating spatial extent, because hailstorms of similar intensity may affect vastly different surface areas.

To support development and refinement of this scale, observations from post-storm forensic damage assessments are combined with a literature review of other natural hazard intensity and magnitude scales (e.g., EF-Scale, Mercalli Scale), including previously proposed hail intensity scales (ANELFA, TORRO), as well as other natural hazard risk assessment scales. These will be further supplemented by concurrent observations of hailstone characteristics from field campaigns.

How to cite: Eng, S., Brimelow, J., and Kopp, G.: Proposed Conceptual Framework for an International Hailstorm Intensity Scale, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-243, https://doi.org/10.5194/ecss2025-243, 2025.

P102

ECSS2025-292

Major tornadoes in the Netherlands: Reconstruction and re-rating using the International Fujita scale

Pieter Groenemeijer, Rob Groenland, Bogdan Antonescu, Michou Baart de la Faille, Rutger Boonstra, Alois M. Holzer, Thilo Kühne, Igor Laskowski, Tomas Pucik, Gerard van der Schrier, Gabriel Strommer, Tanja Renko, and Bram van 't Veen

The Netherlands lie within a broad zone stretching from western France into northwestern Germany where strong tornadoes (rated IF2 and above) occur more frequently than in areas further south and east. Throughout the 19th and 20th centuries, the country experienced several powerful tornadoes, as well as multiple outbreaks that also affected neighboring countries.

Among the most notable events was the 1845 outbreak, which began with a tragic tornado in Montville, France, and included at least two tornadoes in the Netherlands—one of which caused widespread destruction in Zevenbergen (North Brabant). Another devastating tornado struck Borculo (Gelderland) in 1925, followed by an outbreak that impacted eastern Netherlands and nearby regions in North Rhine-Westphalia and Lower Saxony, Germany. The town of Neede (Gelderland) suffered particularly severe damage. In 1950, a very strong tornado tore through the Veluwe forest in central Netherlands, fortunately sparing populated areas.

The last major outbreak occurred over two days, 24 and 25 June 1967, producing a series of violent tornadoes across France (Palluel, Pommereuil, Davenescourt), Belgium (Oostmalle), and the Netherlands (Ulicoten, Chaam in North Brabant, and Tricht in Gelderland). After 1967, a few additional tragic events occurred, including the deadliest: a tornado-induced crash of a regional jet in 1981 near Moerdijk (North Brabant), which claimed the lives of all 16 people on board.

Our objective was to compile a comprehensive overview of these significant tornado outbreaks and, for the first time, assign intensity ratings using the International Fujita (IF) scale where possible. To achieve this, we examined newspaper and media archives, official reports, photographs, and drawings to support our intensity assessments. The work intends to show that violent and deadly tornadoes, although rare, affect the relatively small country of the Netherlands several times per century.

How to cite: Groenemeijer, P., Groenland, R., Antonescu, B., Baart de la Faille, M., Boonstra, R., Holzer, A. M., Kühne, T., Laskowski, I., Pucik, T., van der Schrier, G., Strommer, G., Renko, T., and van 't Veen, B.: Major tornadoes in the Netherlands: Reconstruction and re-rating using the International Fujita scale, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-292, https://doi.org/10.5194/ecss2025-292, 2025.

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P103

ECSS2025-316

Interpreting the damage from the 2022 Canadian derecho

Christoph Gatzen, David Sills, Simon Eng, Lesley Elliot, Aaron Jaffe, Connell Miller, Mark Gartner, and Gregory Kopp

On 21 May 2022, a derecho occurred across parts of Canada. It travelled from south-western Ontario into Quebec. Along its 1000 km long and up to 100 km wide path, more than 40 % of the Canadian population have been affected by the storm. It has been one of the worst hazardous weather events in Canadian’s history, killing 16, injuring 32, and causing power outages for 1.1 million people that lasted up to one month. The total estimated loss of 1.257 billion CAD is among the 10 highest recorded for a natural disaster in Canada.
The nature of the wind damage – specifically the damage mechanism responsible for extreme surface winds - can also help infer low-level storm dynamics and structure. Damage to buildings and infrastructure can indicate differences in wind speed gradients as well as other small scale storm structures which cannot be resolved using remote sensing data. In this event, these mechanisms likely spanned the full gamut of convective wind damage mechanisms (i.e., rear-inflow jet, meso- and miso-cyclones, downbursts/microbursts, and tornadoes), as inferred by wind damage survey data. The Northern Tornadoes Project did numerous damage surveys within the derecho’s path, providing a detailed overview of the derecho’s heterogenous wind damage occurrence. This included a quasi-continuous area of EF1 damage embedded within the derecho, and numerous downburst swaths of EF2 damage. Additionally, 4 tornadoes were confirmed.
Based on this detailed damage analysis, this work addresses the processes that influenced the development of the derecho, in particular according to its path and local intensity. Using radar data, model data, and data of observation networks, we analyse frontal lift, mesoscale lake-sea wind boundaries, the influence of vertical wind shear, and CAPE and CIN distribution in the pre-storm environment, and the location of the rear inflow jet, bow echoes, mesovortices, and pre-storm convection initiation to discuss the influence of these parameters to the derecho development.

How to cite: Gatzen, C., Sills, D., Eng, S., Elliot, L., Jaffe, A., Miller, C., Gartner, M., and Kopp, G.: Interpreting the damage from the 2022 Canadian derecho, 12th European Conference on Severe Storms, Utrecht, The Netherlands, 17–21 Nov 2025, ECSS2025-316, https://doi.org/10.5194/ecss2025-316, 2025.