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.
The ESSL awarded Dr. Robert Davies-Jones with the Nikolai Dotzek Award for his lifetime achievement. Bob Davies-Jones is the first European to receive this prestigious award, to be presented at the upcoming ECSS in Kraków, Poland, where also the regular 2019 Nikolai Dotzek Award will be given.
Bob Davies-Jones is one of the founders of the modern theoretical description of supercell thunderstorms. Although he is perhaps best known for his contributions on supercell and tornado dynamics, he also has advanced the field of large-scale dynamics and made numerous contributions on basic fluid physics (often centered on one of the most important quantities to analyze tornadoes: vorticity).
While much of Europe remains under stable conditions, severe weather outbreak occurred over Antalya province, southern Turkey, between 24th and 26th January 2019. Outbreak included numerous instances of heavy rainfall resulting in flash floods, tornadoes, severe wind gusts and large hail (Fig. 1).
On 24th January, three tornadoes affected the province, one of them rated F2, killing 1 and injuring 6 people. 2 F1 tornadoes occurred as well, injuring 1 person. Tornadoes inflicted considerable damage to homes, roofs and greenhouses.
On 25th January, flash flooding has killed 2 people in the same area.
On 26th January, a strong tornado, rated F2, struck Antalya airport, injuring 11 persons at the site. 8 passengers were injured on a transfer bus that was overturned and dragged by severe winds. 3 airport employees were injured in another shuttle. The event has gained significant attention on the social media as many videos and photographs were taken of the tornado. Tornadic storm would later produce additional F1 tornado and also instances of very large hail, damaging greenhouses.
This tornado outbreak is interesting from two aspects. The first is its occurrence in the middle of winter and out of the convective season throughout much of Europe. However, recent research on tornado climatology (Groenemeijer and Kuhne, 2014; Kahraman and Markowski, 2014) shows that January is actually the month with peak tornado activity over this part of Turkey (Fig. 2). A relatively warm sea with strong flow aloft combined to create marginal CAPE, low cloud bases and pronounced vertical wind shear in the lower troposphere (Fig. 3)
The second interesting aspect is that it shows the potentially high societal impact that tornadoes may inflict when striking vulnerable infrastructure, in this case an airport. Had the tornado been stronger and/or larger, the impact could have been much worse, with hundreds to thousands of people in danger. While tornadoes are considered rare in Europe, this is actually the second time in less than two years that a tornado got in close proximity of an airport, after the Vienna Schwechat airport incident on 10th July 2017. Tornadoes are in general an underestimated threat in Europe (Antonescu et al, 2017) and this recent case demonstrates a strong need to include tornadoes in national weather warning systems.