The full ECSS programme has been published and last preparations are being accomplished for a fruitful 10th edition of the European Conference on Severe Storms in Kraków, Poland, from 4 to 8 November 2019.
ECSS2019 webpage with travel information, online programme and PDF programme overview
A new study, resulting from cooperation of researches from ESSL and Munich-RE, called “Large hail incidence and its economic and societal impacts across Europe” has just been published in the Monthly Weather Review.
This study addresses the large hail incidence in Europe and its economic and societal impacts from multiple perspectives. Two main datasets used in the study were the European Severe Weather Database and the NatCatDATABASE of Munich-RE. While authors acknowledge that ESWD still does not allow for a homogeneous climatology of large hail across whole Europe, one can still learn many things from the data, such as the peak month of large hail occurrence in Europe (Fig. 1), hail size distribution, or how many injuries were reported with large hail.
Damage description that can be entered in the ESWD was used to investigate how the different types of hail damage depend on the reported hail sizes. It was found out that damage to trees, crops or greenhouses is typically reported with hail sizes of 2 – 4 cm in diameter, but damage to roofs, vehicles and windows usually occurs with hail size larger than 4 cm (Fig 2.). Furthermore, damage to vehicle windows was never reported with hail smaller than 5 cm in diameter.
Authors also looked at how hail-related monetary losses have evolved since 1990 over Germany based on the data from NatCatDATABASE of Munich-RE. It was found out that while time serie of annual hail losses is dominated by outliers with very high losses (e.g. the event of 27 to 28 July 2013, which claimed over 4 billions of $ in total losses), the number of annual hail loss days shows a statistically significant rising trend (Fig. 3). Besides increasing vulnerability, the frequency of severe storm environments capable of producing large hail has increased as well, as demonstrated by ARCHaMo models Rädler et al. (2018) applied to the ERA-Interim data.
In the recent days, parts of western and southern Europe have experienced an extraordinary outbreak of severe weather. Between 6 and 10 July 2019, 480 reports were submitted to the European Severe Weather Database (www.eswd.eu). The severe weather included flash floods, large hail, tornadoes, and damaging wind gusts.
During this period, the largest reported hailstones fell on 10 July in Pescara, Italy, and were estimated at 14 cm in diameter. This almost ties the previous record hailstone size in the database, 15 cm, observed on 20 June 2016 in Timișoara, Romania.
The storms had large societal impacts with 10 fatalities (6 in Greece) and 90 injuries (48 in Greece alone, but some media mention that up to 100 people have been injured), mostly from damaging wind gusts and hail. Most fatalities and injuries were reported on 10 July in northern Greece, following a convective windstorm that hit Chalkidiki. The highest number of severe weather reports originated from Italy, where more than 150 reports were collected during the 5 subsequent days of this severe weather outbreak.
What caused such a long-lasting outbreak of severe convective storms that impacted areas like Northeastern Italy several times in a row? The reason was a stalling frontal zone over the Alpine range, which initiated storms in a very moist air-mass with high convective available potential energy (CAPE) that frequently exceeded 2000 J/kg. Such high CAPE values supported strongupdrafts in forming convective storms. At the same time, strong winds in the mid and upper troposphere (between 3 and 10 km above the surface) south of the front, created strong vertical wind shear. The wind shear helped the storms to organize into supercells (storms with rotating updrafts) or intense squall lines and bow-echoes, which are known for the strong winds they can produce. The figure below shows that, high CAPE (colours) and strong vertical wind shear (wind barbs) were collocated over southern Italy and Greece on 10 July. The outbreak only ended as the frontal zone finally moved southeast, followed by drier and cooler air in its wake.
What happened on the individual days of the outbreak? On 6 July 2019 severe weather was reported from France and Italy. Over France, very large hail up to 8 cm in diameter and wind damage occurred. Over Italy, the regions of Friuli-Venezia Giulia, Veneto and Piemonte experienced very large hail. The area nea Vercelli was particularly hard hit with roofs completely destroyed by hail and cars heavily damaged with windows broken out. Severe wind gusts were reported from Switzerland.
7 July 2019 featured the most extensive area of severe weather that occurred in two belts: from southeastern Slovakia to Ukraine and from northeastern Italy towards Romania. Very large hail, up to 7 cm across, was reported from Croatia and a swath of severe wind gusts extended along the Adriatic Sea coastline and from Serbia to Romania. A 32 m/s wind gust was measured in westernRomania in the evening hours and 30 m/s wind gust was measured in Zadar, Croatia overnight. Furthermore, a tornado was reported from Syurte, Ukraine, which occured with a long-lived supercell that also produced very large hail and downbursts over Slovakia.
On 8 July 2019, severe thunderstorms again impacted northeastern Italy with very large hail. However, arguably the most severe weather happened in Spain, where severe flash floods killed a person in the town of Morriones. Besides flash flooding, very large hail up to 8 cm, a F1 tornado and severe wind gusts were reported from the northern part of the country.
The axis of severe weather shifted more to the south on the following day, 9 July 2019. In the afternoon, isolated storms produced very large hail up to 8cm in diameter over Italy. Later on, storms clustered into a large convective system and produced swaths of damaging wind gusts, which extended over the Adriatic Sea towards Croatia, Montenegro and Albania.
The most societally impactful severe weather happened on the last day of the outbreak, 10 July 2019. Day started with an F1 tornado that injured 3 in Milano Marritima, Italy. By the early afternoon, the storms moved south and intensified while producing giant hail, up to 14 cm diameter, injuring 20 people in the Abruzzo region of Italy. In the afternoon, Puglia was impacted by damaging hail and wind gusts.
Subsequently, several of the storms originating over Italy crossed the Adriatic Sea and impacted first Albania and then Greece. Numerous injuries were reported to have resulted from damaging wind gusts and hail. In the evening, the Chalkidiki peninsula was particularly hard hit with 6 fatalities. Some media sources are mentioning over 100 injuries. On the same day, 2 people were also killed by lightning in northwestern Turkey.
This outbreak was quite rare, but it is difficult to say how extraordinary it was, because the ESWD only since 2006 collects observations of large hail and local severe wind gusts, phenomena that often escape detection by traditional observation networks. Analyses of severe weather conditions are showing that severe weather conditions with high CAPE have become more frequent (read more here), and are likely to increase during the century (read more here).
For the ESWD work it is a common question: How can you best estimate and rate the hail size based on photo evidence. The most typical type of hail image is a photo of a person holding a hail stone in the hand.
Therefore the ESWD team around Thilo Kühne compiled a new hail size comparison table. It allows to estimate the hail size in centimeters based on different comparable objects.
Yesterday, 11 June 2019, multiple severe storms occurred over parts of Central Europe. Several of these storms were prolific hail producers and two of them even produced hailstones reaching a diameter of 10 cm or more, which we call giant hail. Such large hail was reported from Gorzów Wielkopolski-Ustronieand Wojcieszyce in western Poland with the largest stone measuring 12 cm. This makes it the biggest oficially measured hailstone in this country according to our partner Skywarn Polska.
Giant hail also occurred in Stari Trg ob Kolpi, southern Slovenia, and Brod Moravice, northern Croatia, with maximum reported hail diameter of 11 cm. This hailstorm actually tracked very close to the path of another giant hail producing storm last year that struck Crnomelj, Slovenia, with hail up to 12 cm in diameter.
With these events ocurring, one might wonder how rare such large hail actually is in Europe. Before 11 June 2019, giant hail was reported 91 times in the European Severe Weather Database (www.eswd.eu) across many different regions in Europe (see figure below) and 42 times since the founding of ESSL on 1 January 2006. Giant hail comprises on only about 0.38% of all large hailreports (minimum diameter 2 cm) submitted to the database. Such hail can cause very serious damage, injuries and occasionally be fatal to humans and animals.
Have we observed even larger hail sizes in the past over Europe? The answer is actually yes: The largest reported hail sizes in recent years are 15 cm on 20 June 2016 in Sânandrei in western Romania and 14.1 cm on 6 August 2013 in Undingen in southwestern Germany.
A new study on the climatology of thunderstorms, “A climatology of thunderstorms across Europe from a synthesis of multiple data sources”, has been published in Journal of Climate. The study was led by Mateusz Taszarek from Adam Mickiewicz University in Poznań and co-authored by Tomáš Púčik and Pieter Groenemeijer from ESSL, among others.
Different datasets were used to investigate the climatology of (severe) thunderstorms across Europe, namely the ZEUS and EUCLID lightning detection networks, SYNOP observations, soundings, ESWD reports and the ERA-Interim data. Weaknesses and strengths of each of the datasets were discussed, as well as similarities and differences in the context of annual number of (severe) thunderstorms days and their annual cycles across various parts of Europe.
For example, the mean annual number of thunderstorm days based on lightning observations over Romania was lower compared to the ERA-Interim dataset, but higher over Hungary, southwestern Slovakia, the Czech Republic and southern Germany. Compared to SYNOP observations, lightning detection networks show higher number of thunderstorm days over most of Europe.
While there were numerous differences between results obtained the individual datasets, the annual cycle was reproduced similarly by all of them. Datasets show that the thunderstorm season peak shifts from south to north from May to August over the continental parts of Europe and then shifts to the Mediterranean area in the autumn. Inland areas of Spain experience the peak in thunderstorm activity in May to June and the eastern coastal areas experience the peak in September to October.