Session 3

South America is known to be a hotspot for severe storms in the world. Environments favorable for severe storms often occur east of the Andes in subtropical latitudes, where extratropical weather systems interact with moisture transported poleward from the Amazon Basin by the low-level jet. This talk will cover research on severe storms in Subtropical South America with focus on the recent efforts to better document and understand severe storms characteristics and environments in the region. The severe storm environments will be discussed and exemplified using recent severe weather outbreaks. Case studies of strong tornadoes indicate that a very strong low-level jet is often present in these environments and these conditions are more common during the cold season. Subtropical South America is also prone to derechos, both serial and progressive. Additionally, giant hail (>10 cm diameter) was broadly documented east of the Andes, with gargantuan hail (> 15 cm) being more restricted to the Andes foothills. The talk will also cover the RELAMPAGO field campaign, which occurred in 2018 in central Argentina. Lastly, a recent international collaboration to maintain a severe storm reports database in South America, as well as efforts to issue semi-operational convective outlooks, will be discussed.

How to cite: Ribeiro, B. Z.: Severe Storms Research and Forecasting in Subtropical South, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-176, https://doi.org/10.5194/ecss2023-176, 2023.

In 1963, Fred Sanders wrote “it is urged the probability be acknowledged as the proper internal language of forecasters.” As such, we can consider all forecasts to be based on probabilities. Nevertheless, as Sanders discussed, issuance of probabilistic forecasts to users is not completely clear. In many cases, users may prefer a categorical forecast and, as such, the internal language of probabilities must be translated into an external language of categorical forecasts. Although there are simple ways to threshold probabilities of a dichotomous (yes/no) event into a yes/no forecast, doing so in a way that is consistent between the two expressions is not always easy. This becomes even more complex when not all users have the same decision threshold and, as a result, may have different preferences for where the optimal threshold is set.

A typical example of this problem is the area of tornado forecasting, especially for short range (<1 hour) forecasts of events, such as is the case for tornado warnings in the United States. Here, I develop and explore some simple (“toy”) models of probability distributions for the forecast and occurrence of tornadoes, as well as the user decision problems. Since each of the three models have one (occurrence given a forecast) or two (forecast probability and distribution of user decisions) parameters, it is relatively easy to construct probabilistic models that can be thresholded to mimic tornado warning performance over time in the United States. In addition, the apparent global benefits (or losses) can be estimated for different probabilistic forecast distributions related to different user decisions compared to dichotomous forecasts.

Although this methodology could not directly produce tornado warnings in an operational setting, it provides some limits on how a future system based on probabilities could be constrained. The process allows for the development of thresholded forecasts that are consistent with the underlying probabilistic information.

How to cite: Brooks, H.: Comparing probabilistic and dichotomous forecasts of hazardous events on a consistent basis: Toy statistical models applied to tornado forecasting, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-2, https://doi.org/10.5194/ecss2023-2, 2023.

As part of the EU COST Action on Mediterranean cyclones, an initiative was launched aimed at defining “Medicane”, a portmanteau for Mediterranean hurricane. In the literature, the term Medicane has been adopted in different ways, depending on the purpose of the study and the instrument adopted for the analysis. The purpose of this activity is to converge towards a shared definition, which will be able to bring together the numerical and satellite approach, the meteorological and climatological perspectives in a single and complete vision.

Although there is still no consensus on the definition, Medicanes are generally considered to be baroclinic cyclones that evolve into vortices with structural characteristics similar to tropical cyclones, i.e., axisymmetric, deep warm core with a windless center surrounded by strong winds. The synergy between baroclinic instability and diabatic processes is fundamental for the intensification of Medicanes.

Stimulating discussions emerged in some online meetings and in the subsequent debate. While up to now the term Medicane has been used for both cyclones with tropical characteristics and for weaker subtropical cyclones, a certain consensus has been reached in considering the latter category as separate, considering the different convective cloud cover, the fact that a significant part of the energy is received from baroclinic sources and that the area with maximum wind is farther from the center.

How to cite: Miglietta, M. M. and the COST Action on Mediterranean cyclones - initiative on the definition of Medicanes: Toward the definition of “Medicane”, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-88, https://doi.org/10.5194/ecss2023-88, 2023.

The availability of various digitized data sources has been steeply increasing during the last 15 years. However, in Finland next to no efforts have been made to gather and normalize weather-related impact data into a single data storage. To fill this gap of information a two-part project called SILVA was carried out in 2020-2022 to scan, collect and store weather-related impact data. In all, a dozen different data sources were identified ranging from electricity supply disruptions and road traffic accidents to airport traffic and train traffic flow anomalies. Most data series covered the whole country and ranged several years back in time. All datasets included time, location, and magnitude or strength of the impact events.

Once the impact events had been stored into the SILVA database they were utilized in various ways. First, some real-time impact data were combined with conventional meteorological data to offer quick impact views for nowcasting purposes (electricity supply disruptions, observed wind gusts and lightning observations etc.). Second, archived impact data and historical ECMWF weather forecasts were used for the training of gradient boosting machine-learning methodology. As a result, seven-day impact-based forecasts for the amount of damage clearance tasks, wildfire fighting tasks, traffic accidents and pedestrian slipping accidents were generated for each Finnish administrative region.

During the latter half of the project a seven-month pilot phase was carried out. More than 30 organizations attended the pilot, and they were provided with real-time weather observations, weather warnings, severe weather outlooks as well as novel impact-based forecasts. During the pilot phase severe weather forecasters gave video briefings ahead of each potentially interesting weather episode to make the users familiar with the pilot products. Briefings were held ten times, prior to blizzard, severe thunderstorm, wildfire, and synoptic-scale windstorm cases.

Preliminary verification results and the feedback gathered from the pilot users have been encouraging. The impact-based forecasts have been warmly welcomed by the users although some expected forecast pitfalls have been reported especially in relation to severe thunderstorm impacts. The users gave an overall rating of 4/5 on the project and rating of 4.3/5 on the future development potential.

Product example: 5-day impact-based forecast on the amount of wind damage clearance tasks for the Finnish administrative regions. Forecast issued on the 6th of August 2022 ahead of an severe thunderstorm event.

How to cite: Punkka, A.-J. and Kämäräinen, M.: Severe Weather Impact Database and Impact-based Forecasts by Utilizing Machine-Learning Technology, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-83, https://doi.org/10.5194/ecss2023-83, 2023.

Until now, studies on lightning fatalities have been available from a few individual countries but not for Europe as a whole. We here report on lightning strike fatalities in the period from 2001 to 2020 that happened across Europe, all of Turkey, the Caucasus countries (Armenia, Azerbaijan, and Georgia), based on reports from the European Severe Storms Database (ESWD). The ESWD records are based on publicly available data derived from local authorities, police and fire departments, newspapers, and news agencies, which are collected by ESSL and its partners.

In total, 1280 individual fatalities were recorded in the ESWD during this period. We report on the spatial distribution of fatalities, and the distribution of fatalities per age group and sex, whether the victims were at work or undertaking leisurely activities, and in which kind of landscape they were hit. Furthermore, we considered the circumstances that led to lightning fatalities that occur indoors.

We found that an average of 64 people are killed by lightning strikes every year, and that the majority (78%) are male. The countries with the highest rate of lightning fatalities per capita are Bulgaria (8.6 per million per year), Moldova (7.7), and Romania (5.8). The lowest rates are found in Belgium (0.1), Malta (0.1), and Portugal (0.1). The proportion of fatalities in work activities increases from Western to Southeastern Europe. When working, people are most typically killed when working on the fields while during leisure, people are most typically killed when hiking. Of the rare indoor fatalities (1.6%), a majority (11 of 15 known cases, 72%) were killed by fire and smoke that broke out after the lightning struck. Referring to the age of fatalities, people at the age of 10-19 have the biggest share of all age decennium with a peak at the age of 15 (33 fatalities). Divided by sex, male fatalities also show the biggest share in the age decade of 10-19, while female fatalities peak in the age decade of 50-59.

How to cite: Kühne, T., Antonescu, B., Groenemeijer, P., and Púčik, T.: Lightning Fatalities in Europe (2001-2020), 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-146, https://doi.org/10.5194/ecss2023-146, 2023.

A previous study on lightning-related human accidents in Europe (2010-2019), estimates that 10% of lightning victims were in a stadium, sports or leisure facility and the vast majority were playing football.

An in-depth analysis of 10 remarkable cases provides information on the thunderstorms responsible for these events: these were not sudden (in 7 out of 10 cases, the thunderstorm has been visible for more than 40 minutes), and the victims were not struck by exceptionally severe thunderstorms (in 6 out of 10 cases, there were less than 10 cloud-to-ground flashes within 10km of the victim) or by intense peak current (in 6 out of 10 cases, the flash was less than the 20kA which is the average value of CG current).

While the victims were children in 5 out of 10 cases, raising questions about the responsibility of adults, the analysis of post-accident declarations reveals at least the ineffectiveness of human judgement in ensuring safety, even though all these events could technically have been the subject of an early warning.

Above all, this fatalism can be counterproductive to any effective awareness-raising by wrongly considering these events as fateful...in the manner of a divine character that we would still attribute to lightning after ages...

How to cite: Schmitt, S.: The risk of lightning strikes in stadiums: the example of football, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-12, https://doi.org/10.5194/ecss2023-12, 2023.

Nowcasting has enormous value and potential in Africa, where populations and economic activity are highly vulnerable to rapidly changing weather conditions, including rapidly developing storms, heavy rainfall and dust storms, which are becoming more frequent and intense with climate change. Timely issuing of warnings, a few hours before an event, can enable the public and decision makers to take action, which can save lives and livelihoods, as well as support national economies. The potential applications of nowcasting across the continent are wide-ranging, and can cover various sectors and activities, including urban warning systems for flash floods, early warnings to fisherfolk at risk from drowning on lakes, protection of crops, water management systems, protection of cattle, aviation warnings as well as the transport sector.

The vulnerability of African countries to weather-related risks make the continent a priority for the development of nowcasting, and is the primary driver for recently published "Guidelines for Satellite-based Nowcasting in Africa". It provides guidelines for the implementation of a range of satellite nowcasting capabilities available for Africa with the advent of the Meteosat Third Generation (MTG) satellite system. The successful launch of the first MTG satellite on 13 December 2022 marks a major improvement over the previous geostationary satellite system. This aligns very well with the UN SG announcement to improve Early Warnings for All, led by the WMO and UNDRR.

The present guidelines are urgently needed, given that there is currently a lack of early warnings on this timescale in Africa. The guidelines aim to provide recommendations that will help facilitate near-term implementation, as well as the development of capacity and sustainability of services overtime. The various options are broken down in the document into different technical, operational, logistical and management aspects. The guidelines can be used to create templates and roadmaps for the establishment and maintenance of nowcasting functions in African countries.

The intended readership includes National Meteorological and Hydrological Services in Africa, Regional Specialized Meteorological Centres, Regional Training Centres, WMO-CGMS VLab Centres of Excellence for Training in Satellite Meteorology, and international agencies.

How to cite: De Coning, E. and Nietosvaara, V.: Guidelines for Satellite-based Nowcasting in Africa, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-95, https://doi.org/10.5194/ecss2023-95, 2023.