ArticlePDF Available


The 1st European Hail workshop took place in Bern in June 2014. The workshop was organized into five topical session i) Convection and hail in a changing climate, ii) Microphysics and dynamics of hailstorms, iii) Hail damage and hail damage prevention, iv) Local probabilities and long-term statistics of hail, and v) Nowcasting and forecasting of hail. This report summarizes the scientific contributions presented and the open scientific questions discussed at the workshop. Available:
BMeteorologische Zeitschrift,Vol.24, No. 4, 441–442 (published online April 13, 2015) Conference Paper
© 2015 The authors
Conference Report 1st European Hail Workshop
Olivia Martius1, Michael Kunz3, Luca Nisi1,2and Alessandro Hering2
1Oeschger Centre for Climate Change Research, Mobiliar Lab for Natural Risks and Institute of Geography,
University of Bern, Switzerland
2MeteoSwiss, Radar, Satellite and Nowcasting division, Locarno-Monti, Switzerland
3Institute for Meteorology and Climate Research (IMK), Karlsruhe Institute of Technology, Germany
(Manuscript received January 9, 2015; in revised form March 6, 2015; accepted March 16, 2015)
The 1st European Hail workshop took place in Bern in June 2014. The workshop was organized into five
topical session i) Convection and hail in a changing climate, ii) Microphysics and dynamics of hailstorms,
iii) Hail damage and hail damage prevention, iv) Local probabilities and long-term statistics of hail, and
v) Nowcasting and forecasting of hail. This report summarizes the scientific contributions presented and the
open scientific questions discussed at the workshop.
Keywords: hail
In recent years, hail damage has increased substantially
in several European regions. Despite the high damage
potential of large hail in the order of billions of Euros,
knowledge on hail frequency, microphysical processes
and temporal variability is still limited. To foster the sci-
entific exchange on this topic, the Oeschger Centre for
Climate Change Research (OCCR), the Karlsruhe Insti-
tute of Technology (KIT), the Mobiliar Lab, and Meteo-
Swiss jointly organized the 1st European Hail Workshop,
which took place at the University of Bern from 25 to
27 June 2014. The overall aim of the workshop was
to bring together scientists working on hail-related re-
search questions as well as practitioners from the oper-
ational weather forecast community and from the insur-
ance industry. The topical scope was intentionally very
broad ranging from fundamental research topics to var-
ious application aspects. The workshop – attended by
more than 130 participants from 18 different countries
and from 21 different operational weather services – was
structured into the following five thematic sessions:
Convection and hail in a changing climate
Microphysics and dynamics of hailstorms
Hail damage and hail damage prevention
Local probabilities and long-term statistics of hail
Nowcasting and forecasting of hail
The detailed program of the workshop and PDFs of most
of the presentations and posters, as well as a recording
of the Nowcasting and Forecasting session are available
from the following website:
Corresponding author: Olivia Martius, Oeschger Centre for Climate Change
Research, Mobiliar Lab for Natural Risks and Institute of Geography, Univer-
sity of Bern, Switzerland, Hallerstrasse 12, 3012 Bern, Switzerland, e-mail:
Convection and hail in a changing
The workshop opened with contributions focusing on
the important topic of convection and hail in a changing
climate, which underlined the big research gap that is
still present in this field of research. The scarce availabil-
ity of reliable long-term information of hail frequency
on the ground hampers the analysis of possible trends in
recent decades. Further on, there is a stark mismatch of
scales between the spatial resolution of state-of-the-art
climate model projections and the scale of the processes
that result in severe convection and hail.
One approach to tackle this problem is to identify the
meso-scale to synoptic-scale environment(s) beneficial
for hailstorm formation and to use these parameters as
proxies for hail in reanalysis or climate model data. Cor-
responding analyses are performed based on local ob-
servations (e.g., sounding data) and gridded re-analysis
and climate model data sets (presentations by Sanderson
et al., Zhang and Li, Mohr and Kunz, Manzato, Pucik
et al., Stoll and Jordi). This approach, however, currently
does not include effects of changing aerosol concentra-
tions or changes in the microphysical processes.
Microphysics and dynamics of
Current challenges in modeling the microphysical pro-
cesses involved in hail formation and melting include
the diversity of ice nuclei (presentation by Hoose), the
representation of internally mixed (partly frozen – partly
liquid) hailstones and their properties (e.g., spongy ice)
(presentations by List, Sant and Seifert), and the fall
speed and terminal velocity of hail and graupel (presen-
tation by Heymsfield and Wright). These challenges can
be addressed through combined efforts in model devel-
opment and high-quality in-situ and laboratory measure-
ments. The further development of improved hail micro-
© 2015 The authors
DOI 10.1127/metz/2015/0667 Gebrüder Borntraeger Science Publishers, Stuttgart,
442 O. Martius et al.: Conference Report 1st European Hail Workshop Meteorol. Z., 24, 2015
physics schemes is also of central importance for numer-
ical weather prediction (NWP) activities (presentations
by Milbrandt and Martynov et al.).
Hail damage and hail damage prevention
A detailed understanding of the microphysical proper-
ties of hail is also the basis for hail suppression at-
tempts. Several hail suppression programs, mainly run
in agriculture intensive areas, using aircraft or ground-
based systems for seeding with silver-iodide were pre-
sented at the workshop (presentations by Foris, Teschl
et al., Berthet and Dessens). All programs include a
combination of hailstorm nowcasting and monitoring
activities, insurance solutions and hail suppression tech-
niques. These programs provide some of the longest ob-
servations of hail occurrence and hailstone properties in
Insurance companies have reported on increasing
trends in hail losses to properties and vehicles in re-
cent decades. The current focus is on the development of
sophisticated hail loss models (presentations by Geiss-
bühler and Ritz, Griesser et al., Schmidberger et al., Vic-
tor et al.). Challenges faced when constructing the loss
models include (i) a lack of direct observational data
(e.g., on hailstone sizes and shapes), (ii) the complex-
ity of the vulnerability of buildings and constructions to
hail (e.g., residential, industrial and commercial build-
ings), and (iii) consideration of the time of the year
(e.g., mature vs. premature crops) and of human ac-
tions (e.g., closing of window blinds) (presentations by
Imhof and Choffet, Heidemann). Hail loss models ap-
ply statistical methods to increase the number of severe
hail swaths beyond available observations (presentations
by Schmidberger et al., Geissbühler and Ritz, Griesser
et al.).
Local probabilities and long-term
statistics of hail
The statistical approach used for hail loss models is
complementary to a series of hail frequency climatolo-
gies that are currently being established in many coun-
tries, mainly based on single polarization radar observa-
tions covering the last 10 to 20 years (presentations by
Nisi et al., Meyer et al., Kunz et al., Lukach and Delobbe,
Rigo et al., Pocakal, Stolaki, Schemm et al.). Using such
data sets requires ground observations (e.g., hail pads,
insurance loss data) for calibration and verification. Ad-
ditional observations are provided, for example, by the
comprehensive archive of the European Severe Weather
Database (ESWD, Dotzek et al., 2009, presentation by
Groenemeijer et al.) that collects hail reports from vol-
untary observers and weather services. Also relying on
voluntary hail reports is the crowdsourcing mPing smart
phone citizen science project, currently established in
the US (Elmore et al., 2014).
Nowcasting and forecasting of hail
The need for and importance of reliable ground obser-
vations have been underlined from the research commu-
nity, the insurance industry, but also from the weather
services. These observations are required for model cal-
ibration and verification of radar- and numerical weather
prediction (NWP) model-based nowcasting tools, but
also for developing and extending radar-based hail prod-
ucts including new dual-polarization products. Now-
casting methods combine radar information with NWP
model output and statistical tools to provide partially
fully-automated hail warnings on time-scales from min-
utes up to a few hours (presentations by Hering et al.,
Auer et al., Winterrath, Kaltenboeck and Ryzhkov).
Nowcasting includes the tracking of hail cells and a pre-
diction of their path. Besides radar data other sources of
remote sensing information such as lightning- (poster by
Rigo and Pineda, presentations by Betz and Moehrlein,
Jurkovic and Mahovic, Schmid) and satellite-based es-
timates of effective radii have proven valuable for now-
casting purposes. Polarimetric radars, finally, offer the
potential to provide further information on the hailstone
size (e.g., Ryzhkov et al. 2013) and shape distribution
and falling behavior, but this still needs some verifica-
tion (presentation by Lakshmanan).
The workshop demonstrated the valuable collaboration
between research and business in a field with scarce data
availability. Research efforts in the next couple of years
should be dedicated to increase the quantity and quality
of hail observations. These efforts will be a combination
of rescuing and processing available data and exploit-
ing new data collection opportunities and new observ-
ing systems (e.g., automatic hail sensors, presentation by
Löffler-Mang et al.). These data sets will be the founda-
tion for improved nowcasting and forecasting systems of
hail, for improved process understanding and the devel-
opment of novel microphysical schemes for NWP and
climate models, as well as for long-term hail frequency
and trend studies.
The organization committee would like to thank the
Mobiliar Lab for Natural Risks for substantial financial
support and the Oeschger Centre for Climate Change
Research for administrative and logistic support. We
thank Hannes Sutter,Monika Wälti,andMichael
Riffler for providing expert logistic support.
Dotzek, N.,P. G r oen e mei jer,D. Feuerstein,A.M. Holzer,
2009: Overview of ESSL’s severe convective storms research
using the European Severe Weather Database ESWD. – At-
mos. Res 93, 575–586, DOI:10.1016/j.atmosres.2008.10.020
Elmore, K.L.,Z.L. Flamig,V. Lakshmanan,B.T. Kaney,
V. Farmer,H.D. Reeves,L.P. Rothfusz, 2014:
MPING: Crowd-Sourcing Weather Reports for Re-
search. – Bull. Amer. Meteor. Soc. 95, 1335–1342, DOI:
Ryzhkov, A.V.,M.R. Kumjian,S.M. Ganson,P. Zhang,
2013: Polarimetric Radar Characteristics of Melting Hail.
Part II: Practical Implications. – J. Appl. Meteor. Climatol. 52,
2871–2886, DOI:10.1175/JAMC-D-13-074.1
... Hailstorms are local and rare events which cause high damages and economic losses to human infrastructure and agriculture in Central Europe (Martius et al. 2015;Munich Re 2007). It should be noted that climatological studies on hail are demanding due to the rather sparse measurement networks on the one hand and the local and short-term characteristics of hail events on the other hand. ...
... Kunz and Puskeiler (2010) combined radar-based hail detection with a cell tracking algorithm and insurance data for the German federal state of Baden-Wuerttemberg. Martius et al. (2015) give an overview about the current hail research in Europe. ...
In the German Strategy for Adaptation to Climate Change hail is identified as one of the major subjects of concern regarding transport infrastructure. Moreover hailstorms are a major threat to e.g. agriculture and the automobile industry causing significant economical damages and losses. Despite these significant hail-related meteorological risks no comprehensive observation-based hail climatology for Germany exists. In this study we present a new approach to this task, combining radar data with different kinds of hail reports, such as ground observation and agricultural insurance data. Preprocessing ensures the applicability of the radar data for the presented climatological analysis. In this sense a number of detection methods are applied to filter artefacts, especially clutter pixels and spokes that disrupt radar measurements. To construct a reliable hail climatology for Germany we process all information into a 10‑year based annual average number of hail days on a 1km×1km$1\,\text{km}\times1\,\text{km}$ grid using a two-path hail criterion. While the first path combines a threshold of 50 dBZ with a hail report, the second path is based on a 55 dBZ threshold only. By adding radar data we increase the spatial representativity of the ground based hail reports and gain additional information in regions which lack observational data. Overall, the results are mainly determined by events derived from the first path (68 %). A validation of our dataset at 65 stations of Deutscher Wetterdienst shows that the method slightly underestimates the number of hail days, especially for mountainous regions. This results in a better adaption of the hail criterion to lowlands. The resulting hail frequency map shows an increase in the average number of hail days per year from north to south. In particular, hailstorms occur less frequently in the Central North German Plain and the Mecklenburg Coastal Lowland, whereas the highest number of hail days occurs mostly in the uplands of the Black Forest and the Swabian Jura, but also in the Rhenish Massif, the Alpine Foreland and the Lower Rhine Plain. Moreover, the Feldberg region in the Southern Black Forest shows the highest number of hail days per year.
... This article approaches the topic of hail in the Earth system by providing a set of perspectives of the areas of research that have been used to inform our understanding. Motivation for this review is driven by recent workshops that have brought together the community in both Europe and North America, which have raised many of the limitations and advances in hail science (e.g Martius et al., 2018;Romppainen-Martius et al., 2015). ...
Full-text available
The processes leading to the development of hail and the distribution of these events worldwide are reviewed. Microphysical and physical characteristics of hail development are described to provide context of the notable gaps in our understanding of what drives hail to grow large, or what determines how it falls to the ground. Distributional characteristics of hail are explored, utilizing both surface observations of hailstones and remotely sensed observational datasets to identify opportunities and needs for new observations. These observational deficiencies contribute to our limited capacity to both forecast hail or its expected size, and reduce the effectiveness of using favorable conditions for hail development as a proxy to frequency where observations are unavailable. Given the substantive influences of both climate variability and the changing Earth system on hail, the latest understanding of their contributions to risk are addressed. Applying this understanding of the distribution and physical characteristics of hail, the damage by hail of agriculture and insured property are assessed. Much remains unknown about the processes leading to hail growth and environmental controls on hail occurrence, size and magnitude, particularly outside of the United States and Europe. A better understanding of the global occurrence of hail is also needed to better anticipate the hazard and associated impacts.
An 8-year analysis of hailstorms is presented. A comprehensive set of six hundred hailstorms that occurred in 172 different days in various parts of Germany is used to characterise these events. The analysed observations include measurements from a lightning location system, precipitation radar, as well as information from automated cell detection algorithms based on radar reflectivity and radial winds which are combined with severe weather reports. Additionally to the storms' parameters during the time of the observed hail, the temporal evolution of the storms' characteristics is analysed in order to study the convective life-cycle and identify parameters with predictive skill. A special focus is on the lightning characteristics of the convective cells. A feature that is shown to occur in many of the analysed severe hail cases is the lightning jump, i.e., a rapid increase in the total lightning density. It occurs well before the observed hail and has thus a great potential to increase the lead time of warnings of severe hail events. Instead of fixed thresholds for the definition of a lightning jump, a lightning jump intensity parameter is introduced and tested. The analysis also reveals that half to the storms show a pulsating lightning activity. Nearly three quarters of the hail events are associated with a mesocyclone that was automatically detected in radar data. As expected, high reflectivity values were measured during the time of the observed hail.
Full-text available
The mobile Precipitation Identification Near the Ground project (MPING) is an app for smartphones that allows citizen scientists to provide observations about winter precipitation type at the surface at least equivalent in quality to human-augmented Automated Surface Observing System (ASOS) observations Among the key features of mPING are immediate feedback to users that their submission has been accepted and the ability to display and even download all submissions using a web-based display. Precipitation type choice is made via a drop-down list or menu. Users simply select the observed precipitation type, at which point the app returns to the submit page. Two taps of the screen are all that is needed to submit an observation once the app is opened. An extra tap is needed for hail because the user must select thehail size using a slider bar. Both the mobile apps and the web page submit information via HTTP to a common database that validates user input and provides persistent storage of the public reports. The app itself is not static, enhancements have already been made and additional mobile platforms may be considered in the future.
Full-text available
The results of theoretical modeling in Part I are utilized to develop practical recommendations for de-veloping the algorithms for hail detection and determination of its size as well as attenuation correction and rainfall estimation in the presence of hail. A new algorithm for discrimination between small hail (with maximal size of less than 2.5 cm), large hail (with diameters between 2.5 and 5.0 cm), and giant hail with size exceeding 5.0 cm is proposed and implemented for applications with the S-band dual-polarization Weather Surveillance Radar-1988 Doppler (WSR-88D) systems. The fuzzy-logic algorithm is based on the combined use of radar reflectivity Z, differential reflectivity Z DR , and cross-correlation coefficient r hv . The parameters of the membership functions depend on the height of the radar resolution volume with respect to the freezing level, exploiting the size-dependent melting characteristics of hailstones. The attenuation effects in melting hail are quantified in this study, and a novel technique for polarimetric attenuation correction in the presence of hail is suggested. The use of a rainfall estimator that is based on specific differential phase K DP is justified on the basis of the results of theoretical simulations and comparison of actual radar retrievals at S band with gauge measurements for storms containing large hail with diameters exceeding 2.5 cm.
Full-text available
Severe thunderstorms constitute a major weather hazard in Europe, with an estimated total damage of 5–8 billion euros each year nowadays. Even though there is an upward trend in damage due to increases in vulnerability and possibly also due to climate change impacts, a pan-European database of severe thunderstorm reports in a homogeneous data format did not exist until a few years ago. The development of this European Severe Weather Database (ESWD) provided the final impetus for the establishment of the European Severe Storms Laboratory (ESSL) as a non-profit research organisation in 2006, after having started as an informal network in 2002. Our paper provides an overview of the first research results that have been achieved by ESSL. We start by outlining the reporting practice and quality-control procedure for the database, which has been enhanced by a major software upgrade in the fall of 2008. It becomes apparent that the state of reporting converges to a realistic description of the severe storms climatology, corroborating, for instance, earlier estimates of tornado occurrence in Europe. Nevertheless, a further rise in the number of reported events must be expected, even without the presence of any physical trends. The European tornado and damaging wind intensity distributions as a function of the Fujita scale are quantitatively similar to long-term distributions from the USA, except for a strong underreporting of weak events (F0) that still persists in Europe. In addition, the ESSL has recently proposed a new wind speed scale, the Energy- or “E-scale” which is linked to physical quantities and can be calibrated. Finally, we demonstrate the large potential of ESWD data use for forecast or nowcasting/warning verification purposes.
Overview of ESSL's severe convective storms research using the European Severe Weather Database ESWD.-Atmos
  • N Dotzek
  • P Groenemeijer
  • D Feuerstein
  • A M Holzer
Dotzek, N., P. Groenemeijer, D. Feuerstein, A.M. Holzer, 2009: Overview of ESSL's severe convective storms research using the European Severe Weather Database ESWD.-Atmos. Res 93, 575-586, DOI:10.1016/j.atmosres.2008.10.020