Session 10 | Storm climatology, risk assessments and relation to climate change

Session 10

Storm climatology, risk assessments and relation to climate change

Orals

| Mon, 08 May, 14:30–18:15 (EEST)|Main Conference Room

Posters

| Attendance Tue, 09 May, 14:30–16:00 (EEST) | Display Mon, 08 May, 09:00–Tue, 09 May, 18:30|Exhibition area

Orals: Mon, 8 May | Main Conference Room

14:30–14:45

ECSS2023-160

Comparing CMIP6 Future Projections for Severe Convective Environments in a Warmed Climate over Australia, Europe and North America

John Allen, Deepak Gopalakrishnan, Carlos Cuervo-Lopez, Robert Trapp, and Eric Robinson

Severe thunderstorms are a global phenomena, producing a variety of hazards that include hail, tornadoes, damaging winds lightning and heavy precipitation. In the present climate, these events produce large losses to property and life. The warming climate is expected to influence these storm attributes, primarily through increasing thermodynamic instability driven by increased atmospheric moisture as warming occurs to near-surface temperatures. However, while a number of studies have explored how the climate system modulates these hazards through changes to favorable environmental conditions, these projections have generally been latitudinally biased away from the subtropics and focused on potentially aggressive warming scenarios. This presents a challenge to our understanding, as many parts of the world that currently regularly experience severe thunderstorms exist in different climate regimes or latitudes, and which exhibit non-linear responses to the warming climate. Hence what is known for some latitudes and warming scenarios may not reflect a complete picture of the expected changes to hazards on a global level.

This presentation seeks to share newly developed insights into the frequency at which environments favorable to severe convection occur in particular regions, with a focus on identifying potential model biases. Extending from historical frequency, how these environments will evolve in response to moderately and strongly warmed scenarios in terms of both climate variability and change as projected using the latest generation of Coupled-Model Intercomparison Project Version 6 (CMIP6) data is explored. Results highlight that increases over the Northern and Western hemispheres are not necessarily reflective of changes in the subtropics and Southern hemisphere, and may respond differently depending on the environmental proxy used. While the driving mechanism of these changes are strong increases in CAPE, these changes can be modulated by local processes, and are often accompanied by factors that either resist convection (CIN), or seasonally may coincide with high likelihood of storm organization (S06, SRH).

How to cite: Allen, J., Gopalakrishnan, D., Cuervo-Lopez, C., Trapp, R., and Robinson, E.: Comparing CMIP6 Future Projections for Severe Convective Environments in a Warmed Climate over Australia, Europe and North America, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-160, https://doi.org/10.5194/ecss2023-160, 2023.

14:45–15:00

ECSS2023-98

Trends of thunderstorm activity and relation to large-scale atmospheric conditions in western and central Europe

Markus Augenstein, Susanna Mohr, and Michael Kunz

Thunderstorms associated with severe weather phenomena such as heavy rainfall, wind gusts, hail, tornados or lightning frequently cause considerable damage across the globe. In light of climate change, it is generally anticipated that the increase in thermal instability due to an increase in low-level temperature and moisture leads to more and more intense thunderstorms, thus increasing the risk from convective storms. However, previous studies have shown high annual and interannual variability of thunderstorm frequency in Europe related to large-scale atmospheric processes and mechanisms such as blocking or teleconnection patterns.

To investigate the relationship between large-scale atmospheric conditions and local-scale thunderstorms and their temporal changes, as well as, their long-term trends, we used cloudto-ground (CG) lightning measurements in western and central Europe from 2001 to 2021 (summer half-year; EUCLID network), representing a spatially and temporally homogeneous dataset. Surprisingly, trend analyses of this dataset show a large contiguous area with significantly decreasing trends from central France to Belgium and the Eifel region in Germany – for both lightning activity and thunderstorm days (defined as at least 5 lightning strokes on a 10 x 10 km² grid). In contrast, significant positive trends occur in northern Spain and some parts of the Balkans. However, in other regions of Europe, the observed trends are not significant due to high annual variability.

Further analyses suggest a relation between large-scale flow characteristics and thunderstorm activity in different regions of Europe. For example, based on odds ratio analyses, episodes with negative values of the North Atlantic Oscillation (NAO) Index are associated with decreasing thunderstorm activity in the above mentioned region (France to Germany). We observed that negative NAO phases, which have occurred more frequently over the last decade, may be an explanation for the negative trends in lightning activity and thunderstorm days.

In addition, we present a new algorithm for the temporal and spatial clustering of CG lightning based on ST-DBSCAN (Spatial-Temporal Density-Based Spatial Clustering of Applications with Noise). This algorithm also filters lightning in low-density regions and thus allows for the detection of contiguous areas of high lightning activity (clustered convective events, CCE). Initial analysis of the newly generated dataset shows that in recent years the number of CCEs with small spatial extent has increased, whereas the number of CCEs with large spatial extent has decreased.

How to cite: Augenstein, M., Mohr, S., and Kunz, M.: Trends of thunderstorm activity and relation to large-scale atmospheric conditions in western and central Europe, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-98, https://doi.org/10.5194/ecss2023-98, 2023.

15:00–15:15

ECSS2023-104

Large-scale flow patterns and their relation to summer lightning in Europe

Homa Ghasemifard, Pieter groenemeijer, Tomas Pucik, and Francesco Battaglioli

This study is a first step in deciphering the role that climate change-induced changes in flow patterns play in the evolution of thunderstorm frequency. Here, we investigate the relationship between large-scale flow patterns and the (temporal and spatial) distribution of lightning in Europe, as recorded by the Met Office Arrival Time Difference Network (ATDnet). The seasonal cycle shows that the largest number of lightning days occurs in summer from May to August, the period we therefore focus on. The large-scale flow pattern is shown using the daily mean 500-hPa geopotentials from the ERA5 reanalysis data. The k-means cluster analysis is applied to the daily mean geopotential heights in the selected four-month period between 1950 and 2020. The algorithm produces 14 patterns. The distributions of lightning associated with the clusters show that lightning frequently occurs under synoptic quiet conditions or even below a ridge. In addition, the occurrence of lightning over Western Europe appears to be more dependent on the synoptic situation, where it is strongly associated with clusters that have a southerly flow in 500 hPa, compared to lightning over the Alpine region or Southeastern Europe. However, changes in the occurrence of synoptic-scale patterns cannot alone explain the changes in the lightning frequency over Europe detected by ARCHaMo (Figure 1). The second reason is that lightning is more dependent on large-scale synoptic-scale patterns in some regions than in others. Across Europe, lightning and lightning ingredients are more strongly tied to individual clusters over the western part than over the eastern part. Therefore, changes in lightning ingredients derived from ARCHaMo are expected to best match changes in lightning frequency derived from changes in clusters over western Europe.

Figure 1: Percent changes in lightning frequency from the average per decade for four months MJJA. Hatching indicates areas where trends are statistically significant. (a) Trend in ARCHaMo due to influence of flow patterns (1950-2020), model values are averaged over the 71 years, (b) Trend in ARCHaMo (1950-2020).

How to cite: Ghasemifard, H., groenemeijer, P., Pucik, T., and Battaglioli, F.: Large-scale flow patterns and their relation to summer lightning in Europe, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-104, https://doi.org/10.5194/ecss2023-104, 2023.

15:15–15:30

ECSS2023-25

Do severe storms across Australia, Europe and the United States share similarities? A comparison of atmospheric profiles and environmental predictors

Mateusz Taszarek, John Allen, Cameron Nixon, Andrew Dowdy, and Francesco Battaglioli

It is well known that atmospheric environments across Australia, Europe and the United States are conducive to the occurrence of convective storms resulting in significant tornadoes, giant hail and damaging winds. However, while many studies have focused on evaluating convective environments over specific regions, only a limited number of elaborations compared different parts of the world. Therefore, in this work we use severe weather reports, ground lightning detection data and ERA5 reanalysis over the last 20 years to address the following research question: do severe storms across Australia, Europe and the United States share environmental similarities? A comparison of composite vertical profiles of temperature, moisture and wind highlighted several consistent features that are common for specific hazards among all three continents. For example, near-ground relative humidity and storm-relative helicity are important for tornadoes while buoyancy in below freezing temperatures and weak near-ground winds are important for large hail. Low-level moisture flux turned out to be the best discriminator between tornadoes and large hail events. However, despite these similarities, statistical analysis indicated that a predictive value for some ingredients can be markedly different among continents. A prime reason for that are different underlying climatological conditions. For example, a strong low-level wind shear combined with sufficient buoyancy is rare over Europe and Australia but when it occurs, it is often associated with tornado reports. On the other hand, a strong low-level wind shear is common over the United States, but is not always associated with proper convective organization to produce a tornado. For this reason, we believe that developing environmental models intended to work universally across the entire world can be extremely difficult as it is challenging to disentangle signals that are associated with physical processes from those that result from a local climatology.

How to cite: Taszarek, M., Allen, J., Nixon, C., Dowdy, A., and Battaglioli, F.: Do severe storms across Australia, Europe and the United States share similarities? A comparison of atmospheric profiles and environmental predictors, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-25, https://doi.org/10.5194/ecss2023-25, 2023.

15:30–15:45

ECSS2023-107

A climatology of drylines and dryline related convection in sub-tropical southern Africa

Lynette van Schalkwyk, Ross C. Blamey, Chris J. C. Reason, Liesl L. Dyson, and Morne Gijben

Surface moisture boundaries or drylines are considered important role players on severe thunderstorm days by South African weather forecasters. On 11 December 2017 one of several thunderstorms which occurred along a dryline, developed into a supercell thunderstorm that resulted in a destructive tornado over the Vaal Marina south of Johannesburg. While the importance of drylines for convection initiation in the region is relatively well understood, the climatological characteristics of drylines and dryline related convection were unknown until recently. Making use of an objective dryline identification algorithm and ERA5 reanalysis data, a climatology of synoptic drylines for the subtropical southern African interior is developed for 1979-2021. The Southern African Plateau (SAP) domain falls within 16-32°S; 18-29°E. Subsequently cloud-to-ground lightning stroke data from the South African Weather Service’s lightning detection network are used to identify days where drylines result in convection between 2010-2021 for a smaller domain within 24-30ºS; 18-24.5ºE. This region is characterized by its high rainfall variability and has some of the highest dryline frequencies in southern Africa. Drylines are found to occur regularly during spring and summer (September - February), almost daily during December, but rarely in winter. Dryline frequencies show large interannual variability with as few as 47 drylines in the summer of 2015/16 of which 38 were convective dryline days, and as many as 73 drylines in the summer of 2016/17 of which 61 were convective. A westward shift in peak dryline frequency takes place through the summer. Drylines peak first over the eastern parts of the SAP during November, but over the central and western SAP during December. Synoptic composite maps are used to gain insight into the different formation environments of drylines that result in convection and those that do not.

How to cite: van Schalkwyk, L., Blamey, R. C., Reason, C. J. C., Dyson, L. L., and Gijben, M.: A climatology of drylines and dryline related convection in sub-tropical southern Africa, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-107, https://doi.org/10.5194/ecss2023-107, 2023.

15:45–16:00

ECSS2023-11

Using convection-permitting simulations to assess future changes in lightning and hail in Europe

Abdullah Kahraman, Elizabeth Kendon, Hayley Fowler, and Jonathan Wilkinson

How lightning and hail will change in the future with global warming is highly uncertain, mainly due to the small space and time scales of these phenomena, which requires high-resolution climate simulations for their accurate representation. Recently km-scale climate simulations have become available that are ‘convection-permitting’ and give the possibility of studying how convective storms may change. We use a pan-European convection-permitting (2.2km grid spacing) model to analyse future changes in deep moist convection, lightning, and hail across Europe under a high emissions-scenario. This includes a physically based lightning prediction scheme, that uses graupel and ice-fluxes that are explicitly represented within the model. It also provides convective-scale outputs, not previously available from conventional climate models, exploited here to study future changes using an ingredients-based approach inherited from severe storm forecasting.

For hail, we derive a new severe hail potential metric that represents the likelihood of hail >2cm at the surface, accounting for hail growth and subsequent melting. Overall, we find an increasing frequency of deep moist convection across Europe mainly due to more instability with warming, but partially limited by greater convective inhibition. However, the increase in storms does not directly translate to an increase in lightning, mainly due to much higher melting level heights resulting in less cloud ice and hence less electrification. Weaker circulation and a northward shift of favourable weather regimes in the future simulation also affects the results, which vary regionally. While lightning increases in future over the mountains (due to enhanced Alpine Pumping) and in the north, lightning decreases over much of central Europe and over the sea. The potential for severe hail generally decreases in future, although storms locally produce higher amounts of graupel in the south. We also identify a new, warmer type of thunderstorms in the future, which may have important implications for changes to the frequency of the largest hailstones.

How to cite: Kahraman, A., Kendon, E., Fowler, H., and Wilkinson, J.: Using convection-permitting simulations to assess future changes in lightning and hail in Europe, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-11, https://doi.org/10.5194/ecss2023-11, 2023.

Coffee break

16:45–17:00

ECSS2023-101

Reconstructing Long-Term (1950-2021) Trends in Convective Hazards using Additive Logistic Regression Models

Francesco Battaglioli, Pieter Groenemeijer, Tomáš Púčik, Mateusz Taszarek, Uwe Ulbrich, and Henning Rust

Additive Logistic Regression Models for different convective hazards were developed across Europe and a portion of North America using lightning observations, severe weather reports and convective parameters from the ERA5 reanalysis. To model convective hazards, convective initiation was taken explicitly into account by computing, for instance, P_hail(probability of hail) as the product of P_storm (probability of convective initiation) and P_hailstorm(conditional probability of hail given a storm). We will report on the development of models that are skilful across Europe and North America, and on the regionally dependent skill of convective parameters used as model predictors. To reconstruct the probability of lightning, large hail, and very large hail from 1950 to 2021, the models were applied to the ERA5 reanalysis, at one hourly intervals across both regions. The modelled hazard climatologies are in strong agreement with observed patterns and can accurately resolve local-scale features thanks to the (0.25 x 0.25° degree) spatial resolution of the ERA5 reanalysis. We analysed long-term trends over the 71 year period and detected important differences between the regions. Across North America, 1950–2021 hail trends were found to be weak and mostly non-significant, but a period of enhanced lightning activity (+30% to 1950–2021 average) was detected between 1980 and 1990 across the Central Plains. In Europe, trends are mostly positive and significant, with the highest trend modelled across Northern Italy. Here, the convective activity has seen an abrupt increase with very large hail 3 times as likely in recent years (2012–2021) than in the 1950s. Apart from a sharp increase in frequency, the year-to-year variability has also increased with yearly differences in occurrence exceeding 100% for large and 200% for very large hail compared to the long-term average. In addition to (very) large hail, preliminary results on the development of models for severe wind gusts and tornadoes models along with the corresponding long-term trends will be presented.

How to cite: Battaglioli, F., Groenemeijer, P., Púčik, T., Taszarek, M., Ulbrich, U., and Rust, H.: Reconstructing Long-Term (1950-2021) Trends in Convective Hazards using Additive Logistic Regression Models, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-101, https://doi.org/10.5194/ecss2023-101, 2023.

17:00–17:15

ECSS2023-55

ENSO Modulation of U.S. Cloud-to-ground Lightning Activity

Kelsey Malloy, Michael Tippett, and William Koshak

Cloud-to-ground (CG) lightning has substantial impacts on human health and property. However, the link between U.S. lightning activity and the El Niño-Southern Oscillation (ENSO), a dominant driver of global climate variability, has not been thoroughly investigated, in part because most lightning datasets sample only a handful of ENSO events. To overcome this limitation, we developed an empirical model of 6-hourly lightning flash count over the U.S. using environmental variables (e.g. convective available potential energy and precipitation) and National Lightning Detection Network data for 2003-2016. This model reproduces the observed interannual variability of lightning over most of the U.S. Then, we used the empirical model to construct a proxy lightning dataset for the period 1979-2021 and investigate the spatial and seasonal patterns of the ENSO-lightning relationship. El Niño is associated with increased lightning activity over the Coastal Southeast U.S. during early winter, the Northwest in the midsummer, and the Southwest during late winter and early spring, whereas La Niña is associated with increased lightning activity over the Tennessee River Valley during February-March.

How to cite: Malloy, K., Tippett, M., and Koshak, W.: ENSO Modulation of U.S. Cloud-to-ground Lightning Activity, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-55, https://doi.org/10.5194/ecss2023-55, 2023.

17:15–17:30

ECSS2023-154

Reconstruction of tornado environments in Romania (1981-2020) using the ERA5 reanalysis

Sorin Cheval, Bogdan Antonescu, Meda Daniela Andrei, Simona Andrei, and Robert-Daniel Manta

The general interest in tornado studies has been stimulated by scientific challenges, such as a better understanding of their genesis and development, and by applications and practical issues, such as forecast, building engineering, and risk analysis.

This context justifies the interest in reconstructing tornado characteristics based on different approaches. The recently released ERA5 reanalysis data set at 31 km-horizontal resolution, and hourly temporal resolution holds significant potential for many climate applications.

In this paper, the tornado environments in Romania between 1981-2020 are reconstructed using a series of thermodynamic and kinematic parameters (e.g., 0-1 km bulk wind shear, 0-6 km bulk wind shear, 0-500m mixed-layer CAPE, ML WMAX*SHEAR) calculated based on ERA5 data. A previous paper on the climatology of tornadoes in Romania showed that in the 1980s there was a minimum in the tornado activity (1 tornado report) followed by a period with a large number of reports (138 reports, approximately 4 tornadoes per year). The aim of the paper is twofold. First, we want to investigate the changes in the occurrence of tornado environments in Romania and thus understand if the minimum in tornado reporting in 1980 is due to tornadoes being ignored by the researchers and meteorologists (and reported as swerve wind events) or natural variability. Second, to study the spatial and temporal variability of the tornadoes in Romania in relation to large-scale patterns. The results show that the frequency of occurrence of tornado environments has increased in Romania since 1980, especially over southeastern Romania.

This work has been financed within project „Dezvoltarea Centrului de Competență pentru Adaptarea Comunităților Locale la Schimbările Climatice prin parteneriate de tip public-privat în domeniul CDI” cod 3/16.11.2022 finanțat prin Planul Național de Redresare și Reziliență Apel nr. PNRR-III-C9-2022 – I5"

How to cite: Cheval, S., Antonescu, B., Andrei, M. D., Andrei, S., and Manta, R.-D.: Reconstruction of tornado environments in Romania (1981-2020) using the ERA5 reanalysis, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-154, https://doi.org/10.5194/ecss2023-154, 2023.

17:30–17:45

ECSS2023-117

Derechos in Finland

Jenni Rauhala

Derechos are long-lived convective wind events that cause damage in vast areas. Since little was known before about derecho occurrence in Finland, the purpose of this study was to search for previously unidentified derecho events and describe derecho occurrence and characteristics in Finland. Derechos were identified by comparing radar reflectivity development of convective storms to the maximum wind gust measurements and reported wind damage. Based on results of this study, derechos are not as rare events in Finland as has been previously assumed. In the preliminary dataset derechos have been observed in Finland from June to October. Compared to other types of convective severe weather, derechos are long lasting events, with their duration in Finland ranging in our dataset from 4h 30 min to 9h 30 min. The length of the observed derecho tracks in Finland varied between 400 km and 660 km. The often-used criteria to search and classify derecho cases based on wind gust measurements of 25 m/s or more, seem not to be very effective in Finland. Even many of the major events, with vast wind damage areas identified by emergency reports of wind damage, would end up having few if any ≥25 m/s gusts measured. The challenge of identifying events that cross country borders, move over open sea or low population areas, is also discussed.

How to cite: Rauhala, J.: Derechos in Finland, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-117, https://doi.org/10.5194/ecss2023-117, 2023.

17:45–18:00

ECSS2023-56

Hail time series from radar proxies for decadal variability of hail in Switzerland

Lena Wilhelm, Olivia Martius, Katharina Schröer, and Cornelia Schwierz

In Switzerland hail regularly causes substantial damage to agriculture, cars, and infrastructure. However, addressing hail damage is challenging, as hail is related to severe thunderstorms, one of the most complex atmospheric phenomena due to its small spatial scale, vigorous development, and intricate physical interactions. In a changing climate, hail frequency and its patterns of occurrence may change, with potentially negative ramifications, e.g. when considering agricultural losses. According to the new Swiss hail climatologies (Madonna et al. 2018; Nisi et al. 2016; Nisi et al. 2020) there is a significant difference between the interannual hail variability on the north and south sides of the Alps. Understanding the drivers of this variability is essential for possible adaptation strategies. In contrast to North America, where important drivers of interannual variability of severe convection are well studied (see Tippett et al. 2015 and Allen et al. 2020), a comprehensive analysis of the year-to-year variability of hail in Switzerland has only been done for the last 20 years (in preparation by Katharina Schröer²). A long-term analysis, however, is still missing.

Therefore, this study presents a daily hail time series for Northern and Southern Switzerland from 1950 to today. The time series is produced from radar hail proxies and ERA-5 reanalysis data. Daily POH (Probability of Hail) data from MeteoSwiss is used to identify haildays in the region north and south of the Alps (plus 140km radar buffer) from 2002 to 2021 for the hail months April - September. The decision hailday yes/no is based on surpassing a POH ≥ 80 for a certain minimum footprint area of the domains. Then, a logistic regression model is constructed for each domain to predict the occurrence of a hailday depending on various environmental variables and indices. 70 different variables were tested. The predictors were chosen based on model performance, collinearity, and expert judgement. With the two best models, haildays are reconstructed back to 1950 for each region. The time series is then used to study the local and remote drivers of interannual variability, e.g. central European weather types, large-scale variability patterns, etc., as well as to investigate past changes or shifts in hailstorm seasonality. With this knowledge, we could improve our understanding of the meteorological-climatological variability, and, with the help of climate scenarios, infer about possible changes in the future.

How to cite: Wilhelm, L., Martius, O., Schröer, K., and Schwierz, C.: Hail time series from radar proxies for decadal variability of hail in Switzerland, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-56, https://doi.org/10.5194/ecss2023-56, 2023.

18:00–18:15

ECSS2023-15

Risk Assessment for Hail Damages to Buildings and Cars in Switzerland: Current Risk and Future Projections

Timo Schmid and David N. Bresch

Hail is a severe meteorological hazard that can cause significant damage to both buildings and cars. Here, we present the first-ever open-source risk model for hail damages, provided within the CLIMADA framework. The availability of high-resolution radar-based hail intensity measures and detailed damage and exposure data from local insurance companies in Switzerland allows for a spatially explicit calibration of vulnerability functions for buildings and cars. The model is able to provide climatological evaluations of hail risk and real-time hail damage estimates based on any user-provided exposure data. Furthermore, combined with crowd-sourced hail reports, the detailed damage data allows for an evaluation and uncertainty quantification of different radar-based hail intensity measures. Results highlight the limitation of radar-based state-of-the-art hail size estimates, such as Maximum Expected Severe Hail Size (MESHS), for accurate risk assessments of hail damages. In a second step, the model will be expanded to use high-resolution convection resolving simulations with the hail growth module HAILCAST as hazard variable. This enables the assessment of hail risk under climate change, when driven by 2-km nested climate simulations following a pseudo global warming approach. This submission is part of the scClim project (https://scclim.ethz.ch/), which seamlessly couples kilometer-resolution weather predictions and climate simulations with hail impact assessments for multiple sectors.

How to cite: Schmid, T. and Bresch, D. N.: Risk Assessment for Hail Damages to Buildings and Cars in Switzerland: Current Risk and Future Projections, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-15, https://doi.org/10.5194/ecss2023-15, 2023.

Posters: Tue, 9 May, 14:30–16:00 | Exhibition area

Display time: Mon, 8 May, 09:00–Tue, 9 May, 18:30

P27

ECSS2023-3

Trends of sounding-derived indices and observations in NE Italy in the last 30 years

Agostino (Tino) Manzato, Gabriele Fasano, Andrea Cicogna, Francesco Sioni, and Arturo Pucillo

High vertical resolution soundings observed at 00 and 12 UTC during the months of April to September of 30 years (from 1992 to 2021) are analyzed to characterize the potential instability, dynamic conditions and moisture conditions of the atmosphere above NE Italy. Their climatological trends are studied, finding that the potential instability and moisture (including the precipitable water) show a robust and statistically significant increasing trend, producing a more favorable environment for storm development. Winds do not substantially change, apart from the meridional component of the low level wind, that causes a positive trend also in the wind shear.

Despite these significant increases in instability and moisture variables, the corresponding observations, in terms of rainfall (from a network of rain gauges), hail (from a network of hailpads) and cloud to ground lightning flashes (from the EUCLID lightning detection network), do not show similar trends. Instability indices describing pre-convective environment are often assumed to trace the storm probability, so that their climatological change is used as a proxy for the probability of storm occurrence and/or intensity. Our findings cast doubts on the validity of this approach, at least locally, because to a strong increase of sounding derived indices (toward a more unstable environment) does not correspond an equally robust increase of the observed storm activities.

How to cite: Manzato, A. (., Fasano, G., Cicogna, A., Sioni, F., and Pucillo, A.: Trends of sounding-derived indices and observations in NE Italy in the last 30 years, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-3, https://doi.org/10.5194/ecss2023-3, 2023.

P28

ECSS2023-43

Assessment of extremes hazards during thunderstorm in France 2000-2019

Nathalie Bertrand and Adrien Gaonac'h

The estimation of natural hazard levels must be considered for the protection of industrial sites for important safety issues. Our study estimates the occurrence, the spatial extension and the concomitance of natural hazards (rain, wind, hail and lighting) during thunderstorm over France during the period 2000-2019.

A thunderstorm is an atmospheric convective instability. In general, a thunderstorm needs a warm and humid air mass to rise in an unstable atmosphere under the effect of some kind of forcing initiating a more or less deep humid convection leading to the formation of cumulonimbus. Depending on the characteristics of the air mass and the wind regimes at different altitude levels, thunderstorms will be of different natures and will produce different types of hazards with a certain intensity: heavy rain, lightning discharges, hail, strong wind gusts and sometimes tornadoes. A severe thunderstorm is defined by the occurrence of at least one of the following conditions: heavy rain, hail with a diameter of more than 2 cm, wind gusts above 25 m/s and tornadoes.

Hence, the study considers all the available data and project them on the same grid (Meteorage lightning grid with 25 km resolution). A thunderstorm event is defined when more than ten lightning are observed on the same day. Then, the probabilities and conditional probabilities knowing the occurrence of a thunderstorm were derived for each hazard over the period and by seasons. It emerges that the regions particularly affected by thunderstorms and their hazards are in a diagonal going from south-west to north-east France, the mountains areas during the warm seasons and the Mediterranean region, the Cevennes during hot and cold seasons especially in autumn with the Mediterranean event which brings heavy rainfall due to the influence of the sea and the proximity with the mountain. However, although it seems that thunderstorms are more frequent over the decade 2010-2019 than in the years 2000-2009, it is difficult to draw a conclusion on the evolution and intensity of these events over such a short period with the inter-annual variability.

To go further, the study explores the potential of the so-called "self-organising" map to describe the different synoptic scenarios leading to these extreme events and their combinations.

How to cite: Bertrand, N. and Gaonac'h, A.: Assessment of extremes hazards during thunderstorm in France 2000-2019, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-43, https://doi.org/10.5194/ecss2023-43, 2023.

P29

ECSS2023-136

An updated tornado climatology and associated meteorological environments in Greece

Michalis Sioutas, Stavros Dafis, George Papavasileiou, and Robert Doe

Tornadoes are common in Greece, as they have been reported in many parts of the country, including continental and maritime areas. Systematic records of tornado occurrences have been collected in the last 23 years, offering to the development of the Greek tornado database and the establishment of relevant climatologies for Greece and Eastern Mediterranean. The 23-year data of the Greek tornado database (2000-22) includes a total of 1435 days with 2086 tornado events. The vast majority of the database, a total of 1485 events, are tornadoes over the sea, the so-called waterspouts, 365 are land tornadoes and 236 are funnel clouds.

An updated tornado climatology is presented for Greece based on the geographical spatiotemporal analysis of tornado, waterspout and funnel cloud occurrences with mapping of the events and investigation of frequency distributions. Further climatological aspects are highlighted, including tornado prone areas, tornado intensity, path scales, damage characteristics and remarkable cases with outbreaks in sequence of days and number of events. Climatological analyses identified western Greece, the Ionian Sea and lowland prairies and coastal areas as most prone to tornado activity. In the Aegean Sea, waterspouts are reported from many places, with a maximum frequency from the north coast of Crete. Strong damaging tornadoes are mostly products of warm season severe thunderstorms, occasionally with supercell characteristics and also by mesoscale convective systems associated with frontal activity.

Synoptic circulation patterns associated with tornado occurrence are identified and categorized into six specific upper-air synoptic flow types, namely: southwest flow (SW), northwest flow (NW), closed-low system (CLOSED), cut-off low (CUT), shortwave trough (SWT) and longwave trough (LW). Mesoscale environments are also investigated based on thermodynamic, dynamic, wind parameters and convective instability indices.

The results help improves a forecasters’ ability to identify and anticipate such extreme weather events, by providing critical background information to the operational forecasting. Establishing synoptic climatologies can be useful in identifying weather conditions associated with tornadoes, possibly not the same as in the USA or other parts of the world with significant tornadic activity. Furthermore, it is important to improve our knowledge about meteorological environments favoring tornado occurrence in the view of the climate change that possibly has a large influence on such extreme weather phenomena.

How to cite: Sioutas, M., Dafis, S., Papavasileiou, G., and Doe, R.: An updated tornado climatology and associated meteorological environments in Greece, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-136, https://doi.org/10.5194/ecss2023-136, 2023.

P30

ECSS2023-70

Enhanced climatology of large hail in the UK: Radar-derived diurnal cycle and storm mode

Henry Wells, John Hillier, Freya Garry, Nick Dunstone, Huili Chen, Abdullah Kahraman, William Keat, and Matthew Clark

Large hail, with a diameter of at least 20 mm, is a hazard associated with severe convective storms (SCS) that can cause significant damage. Understanding of atmospheric environments conducive to large hail is underpinned by catalogues of past events. Because of the small footprint of hail events, these often rely on crowdsourced reports. In the UK, the relative rarity of large hail and low public awareness of SCS hazards makes obtaining a complete set of reports difficult, and in many cases the precise time of the hail is not recorded. In this study, the two major databases of UK large hail reports are merged for the first time. Composite radar reflectivity data are used to verify and enhance 260 reports since 2006. Time of the hail and the basic storm mode (isolated, clustered or linear) are visually estimated from animations. Compared to the UK’s most severe historic hailstorms (1800–2004), our quality controlled climatology of all sizes of large hail shows a diurnal cycle with a slightly broader peak. Around 55% of large hail events are associated with isolated cells, while 34% have supercellular characteristics, a much lower proportion than found in the USA. The full event set (1979–2022), comprising over 850 reports, is used to update the seasonal, spatial and size distributions of large hail in the UK. We intend that this hail event set forms part of a multi-hazard analysis of UK SCS, also including tornadoes and extreme rainfall, and its relationship to background atmospheric conditions. The effect of climate change on UK SCS will be investigated through past and future trends in these background conditions.

How to cite: Wells, H., Hillier, J., Garry, F., Dunstone, N., Chen, H., Kahraman, A., Keat, W., and Clark, M.: Enhanced climatology of large hail in the UK: Radar-derived diurnal cycle and storm mode, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-70, https://doi.org/10.5194/ecss2023-70, 2023.

P31

ECSS2023-24

Severe convective events in Russia: observed changes based on various data

Alexander V. Chernokulsky

Changes in the frequency and intensity of severe convective events, including heavy showers, thunderstorms, hail, squalls, and tornadoes are analyzed for the Russian regions for the warm season based on various independent sources of information. Surface observations from Russian meteorological stations for the period 1966–2020 are used to analyze the frequency of thunderstorms, hail, and strong winds, the amount of cumulonimbus clouds, as well as contribution of extreme showers to the total amount of precipitation. Satellite data are used to estimate the frequency and intensity of tornado and squall events that caused windthrow (for 1986–2021) and the deep convection cloud top height (for 2002–2021). Based on the data of the ERA5 reanalysis, the frequency of occurrence of conditions favorable for the development of moderate and intense convective events is analyzed. The results of the analysis highlight a general intensification of severe convective events in the majority of Russian regions except for several regions in the south of European Russia. The frequency of occurrence of moderate events tends to decrease, while those of strong events tend to increase. A general intensification of severe convective events in Russia is also confirmed by the available results of regional studies in this research area.

How to cite: Chernokulsky, A. V.: Severe convective events in Russia: observed changes based on various data, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-24, https://doi.org/10.5194/ecss2023-24, 2023.

P32

ECSS2023-9

Tornadoes in France since 1900: A chronology and spatial analysis.

Matthieu Lacroix, Yanni Gunnell, and Saïda Kermadi

Since 1900, France has recorded annually 22 tornadoes of low to moderate intensity. Here we investigate the spatial distribution and seasonal patterns of these tornadoes, and document some of the meteorological situations in which they have occurred. We further produce (i) a synthesis of the areas where thunderstorms are formed, with the aim of better understanding the environments favourable to thunderstorm development in France; and (ii) a national tornado risk map emphasising areas exposed to tornadoes in relation to population density. The results of this study are based on data from the Météo-France major events repository (BDEM), the European Severe Storm Laboratory (ESSL/ESWD), and the Keraunos database. This combination results in a complete inventory covering the period 1900-2022. The events selected for the study were analysed in a Geographic Information System, and data from different meteorological reanalyses, such as the GPM IMERG (NOAA NCEP/NCP) and ERA 5, were used for defining the formation zones of a selection of tornado events in the highly affected region.

The spatial distribution of tornadoes in France highlights three vulnerable areas: the north (Normandy, Flanders), the Atlantic west (Poitou, Charentes) and the Mediterranean coastal belt (Languedoc, Provence, NE Corsica). Whereas monthly results highlight a systematic concentration of tornadoes during the warmer season, their spatial distribution appears to be a function of topography- and land-cover-related factors. Specific zones of tornadic storm formation over the Bay of Biscay and the Mediterranean Sea also feature prominently, and these are expected to continue generating tornadoes in the future. The high-risk areas include densely populated urban regions, especially in northern France and near the Mediterranean.

How to cite: Lacroix, M., Gunnell, Y., and Kermadi, S.: Tornadoes in France since 1900: A chronology and spatial analysis., 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-9, https://doi.org/10.5194/ecss2023-9, 2023.

P34

ECSS2023-37

Convective indices trends in Cyprus

Dragos Ene, Rodanthi-Elisavet Mamouri, Argyro Nisantzi, Silas Michaelides, Diofantos Hadjimitsis, Bogdan Antonescu, and Patric Seifert

Recent studies have shown that the Eastern Mediterranean and the Middle East are regions strongly affected by climate change, with a rate of warming two times faster than the global average. While climate change comes with major implications, including the fact that severe storms will become more virulent and more often, studies showed that the annual number of cyclones in the Mediterranean region tends to remain constant in the near future, with no visible trend.

In this paper, we are studying the trends for convective indices in the region of Cyprus, with modelled, and also observational data. For the modelled data, we are using the CORDEX dataset for convective potential energy and convective inhibition with 3h temporal resolution, for the historical period (1971 - 2000), and for the near future (2021 - 2050), from which we extracted the daily maximum and mean values.

Observational data is used from the ESWD database, reports on tornadoes, hail and heavy rain, together with radiosonde data from Athalassa station (radiosonde available in high-resolution mode from 2016, with two launches per day, at 05:00 and 11:00 UTC). Using the Python packages SHARPpy and MetPy we computed the convective indices from radiosounding data.

It is estimated that two tornadoes and three waterspouts occur each year in Cyprus, and in a study from 2006 describing two tornadoes outbreaks from January 2003 and January 2004, these events had CAPE index 411 J/kg and 210 J/kg, and respectively lifted index of -2 and 0.

The authors acknowledge the ‘EXCELSIOR’: ERATOSTHENES: EΧcellence Research Centre for Earth Surveillance and Space-Based Monitoring of the Environment H2020 Widespread Teaming project (www.excelsior2020.eu). The ‘EXCELSIOR’ project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 857510, from the Government of the Republic of Cyprus through the Directorate General for the European Programmes, Coordination and Development and the Cyprus University of Technology.

How to cite: Ene, D., Mamouri, R.-E., Nisantzi, A., Michaelides, S., Hadjimitsis, D., Antonescu, B., and Seifert, P.: Convective indices trends in Cyprus, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-37, https://doi.org/10.5194/ecss2023-37, 2023.

P35

ECSS2023-52

Influence of Moscow megacity on severe atmospheric convective events: results of high-resolution modeling for multiple summers

Vladimir Platonov, Alexander V. Chernokulsky, Mikhail Varentsov, Andrey Shikhov, and Yulia Yarinich

During the warm season in the Moscow region, severe convective events like squalls, heavy showers, large hail, and tornadoes are regularly observed. Moscow megacity may intensify such phenomena due to various urban effects including modulation of heat and moisture fluxes. To quantitatively estimate this effect, we used datasets from two long-term numerical experiments based on the high-resolution COSMO-CLM mesoscale model (grid size ~1 km, output step 1 hour) for the summer seasons of 2007–2016. Experiments differ by switching on/off the urban canopy layer parameterization of TERRA_URB (labeled as URB and noURB, respectively).

We analyzed the maximum surface wind speed, the vertical component of wind speed at different levels, the hourly intensity and daily precipitation amount, and high quantiles for wind and precipitation. To analyze the possibility of mesocyclones formation, we used the Updraft Helicity (UH25) parameter.

We revealed statistically significant differences between the two experiments for the distributions of intense precipitation, vertical wind speed, and the UH25 parameter. The URB experiment showed an increase of the highest quantiles, standard deviations and partially mean values directly above Moscow and to the northeast of the city, in the leeward region compared to the noURB experiment. The compound events were analyzed as well (when both extreme precipitation and extreme surface wind speeds were noted). We found a statistically significant growth of compound events frequency for URB sample and inside the 18-km radius around the center of Moscow indicating the influence of the city.

How to cite: Platonov, V., Chernokulsky, A. V., Varentsov, M., Shikhov, A., and Yarinich, Y.: Influence of Moscow megacity on severe atmospheric convective events: results of high-resolution modeling for multiple summers, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-52, https://doi.org/10.5194/ecss2023-52, 2023.

P36

ECSS2023-57

Empirical Relationship between U.S. Tornado Outbreak Probabilities and the Large-scale Environment

Kelsey Malloy and Michael Tippett

Tornado outbreaks – when six or more tornadoes occur within a short period of time – are rare yet impactful events. It would be advantageous to understand how tornado outbreak activity varies on the subseasonal-to-seasonal (S2S) timescale. We examined the question of whether conditions favorable for outbreaks could be distinguished from those favorable for non-outbreak tornadoes. We have developed a 6-hourly tornado outbreak index, which uses logistic regression to relate the probability of a tornado outbreak at every grid point over the U.S. to collocated values of convective precipitation, storm relative helicity (SRH), and convective available potential energy (CAPE). Storm report data from the Storm Prediction Center is used to train the model and evaluate its performance. We found that this tornado outbreak index represents the climatology, seasonal cycle, and interannual variability of tornado outbreak activity well. Overall, greatest skill of the index is exhibited over regions and seasons when tornado outbreaks occur most often, especially in the Tennessee River Valley and Southeast U.S. for late winter and spring. In terms of reliability, the index performs well for probability forecasts up to 10% but is overconfident for forecasts greater than 10%. We found that the El Niño-Southern Oscillation (ENSO) modulates the tornado outbreak index values via its influence on precipitation, SRH, and CAPE patterns. Therefore, ENSO may be a valuable source of S2S predictability for tornado outbreak activity.

How to cite: Malloy, K. and Tippett, M.: Empirical Relationship between U.S. Tornado Outbreak Probabilities and the Large-scale Environment, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-57, https://doi.org/10.5194/ecss2023-57, 2023.

P37

ECSS2023-61

Powerful winds in Lithuania in 1961-2022 and catastrophic cases in winter 2022

(withdrawn)

Izolda Marcinoniene

P38

ECSS2023-81

Convective environment in ALADIN Reanalysis

Martin Vokoun and Petr Zacharov

In the framework of the national project PERUN (Prediction, Evaluation and Research for Understanding National sensitivity and impacts of drought and climate change for Czechia) new ALADIN (Aire Limitée, Adaptation Dynamique, Development International) Reanalyses are now available for the evaluation purposes. The reanalyses use boundary conditions from European reanalysis ERA5, the first reanalysis uses an assimilation of various meteorological every six hours. The domain of the reanalyses covers Europe with 2.3 km of horizontal resolution. As the evaluation domain we use primarily the area of the Czech Republic.

The reanalysis contain, among other things, outputs describing the convective environment in a 25-year series (1990-2014). The aim of this work is evaluation of CAPE (Convective Available Potential Energy), CIN (Convective INhibition) and wind shear data, as the key values for convection formation. These data are assessed in the perspective of the common temporal and spatial characteristics. Within this study, reanalysis data were verified by sounding data at least from meteorological station Praha-Libuš. These results will be applied for comparison with the ALADIN climate model for period 2025 – 2100. This run use boundary conditions from the climate model CMIP6 with scenario SSP5-8.5 where emissions follow a worst-case pathway until 2040 from all other emission scenarios.

How to cite: Vokoun, M. and Zacharov, P.: Convective environment in ALADIN Reanalysis, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-81, https://doi.org/10.5194/ecss2023-81, 2023.

P39

ECSS2023-87

Climatological aspects of quasi-linear convective systems across Europe

Artur Surowiecki, Natalia Pilguj, Mateusz Taszarek, Krzysztof Piasecki, and Tomas Pucik

In this work, we use 8 years of OPERA radar data, ESWD severe weather reports, and ATDnet lightning detection data to create a climatology of quasi-linear convective systems (QLCS) across Europe. In the first step, 15-minute composite animations of radar reflectivity and lightning data were used to manually identify 2201 QLCS polygons in the period of 2014 to 2021. Severe weather reports, lightning data, and morphological properties (such as the presence of bowing segments) allowed classifying QLCSs according to their intensity into 1844 marginal, 304 moderate, and 53 derecho cases. The manual evaluation also allowed us to identify: the basic archetype of the system, the location of stratiform precipitation relative to the active convective part, propagation with respect to the mean wind, areal coverage, width, length, accompanying hazards, and social impacts associated with each QLCS. Results indicate that QLCSs are the most frequent during summer in Central Europe, while in southern Europe the season of their occurrence is extended to late autumn. QLCSs are the least frequent during winter when they appear mostly in northwestern Europe in the form of narrow cold frontal rainbands (NCFR). In spring they are most common across western Europe. The vast majority of systems move from southwest and west. 22% of the systems were associated with a bow echo signature and 6% produced a mesoscale convective vortex. Among precipitation modes, trailing (53%) and embedded (45%) stratiform types were the most common. The longest classified QLCS had a length of 2200 km (9 Aug 2018), while the widest reached 1635 km (10 Jan 2015). The most frequent hazard accompanying QLCSs was lightning (produced during 95% of the total QLCSs lifetime), followed by severe winds gusts (7.7%), excessive precipitation (5.3%), large hail (2.7%), and tornadoes (0.4%). Derechos had the largest coverage of severe wind reports with respect to their path area (49%), while back-building QLCS had the largest coverage of excessive precipitation events (12%). Large hail was most common with bow-echo complexes (6.5%).

How to cite: Surowiecki, A., Pilguj, N., Taszarek, M., Piasecki, K., and Pucik, T.: Climatological aspects of quasi-linear convective systems across Europe, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-87, https://doi.org/10.5194/ecss2023-87, 2023.

P40

ECSS2023-118

Climatology of derechos and wind squalls in Czechia during the last 25 years

David Rýva

Derechos are well known as originators of widespread and significant damage associated with larger convective storms. Damage caused by derechos can be comparable with damage produced by tornadoes, locally even with strong tornadoes, but an affected area is much larger. As a result, derechos are able to cause significant damage to property, crops, forests etc. They are also able to cause numerous injuries and even fatalities. The research activities of some authors in Europe during the last two decades have shown that derechos are not rare in Central Europe.This study presents detailed results of our research on the occurence and characteristics of derechos and other large scale convectively induced wind squalls in the Czech Republic during warm seasons of the last 25 years (1998 - 2022). We have used our own software tools to identify all convectively indiced wind events. Newly we also used GIS software tools to create better and more complete spatial analyses and climatology of derechos and occurence of convective wind storms. Cold season events were rejected from our study because they usually are a part of a large, synoptic scale, wind storms and it is not easy to distinguish between convective or nonconvective wind gusts. The comparison with the US climatology shows that derechos here in the heart of the Central Europe are almost as frequent as in the continental US and that they definitely should be taken into account in weather forecasts and also in a weather risk assessment.

How to cite: Rýva, D.: Climatology of derechos and wind squalls in Czechia during the last 25 years, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-118, https://doi.org/10.5194/ecss2023-118, 2023.

P41

ECSS2023-120

The climatology and nature of warm-season convective cells in cold-frontal environments over Germany

George Pacey, Stephan Pfahl, Lisa Schielicke, and Kathrin Wapler

Cold fronts provide an environment particularly favourable for convection in the mid-latitudes with advection of low-level moisture, synoptic-scale ascent and modification of atmospheric instability among some of the most important mechanisms. However, the importance of different mechanisms at different locations relative to the front (i.e., pre-frontal, frontal and post-frontal), is not currently well-understood. Cold-frontal convection has attracted the attention of several case studies but spatial and temporal climatologies over longer timeseries of data are very limited, especially during the warm-season. A further question of interest is how cold-frontal environments may alter the nature of convection in terms of convective organisation, cell intensity and the associated convective hazards.

By combining automatic front detection methods and the KONRAD cell detection and tracking algorithm a climatology of cold-frontal convective cells is produced in Germany between 2007–2016 for April–September. We find that on average around twice as many cells develop on cold-frontal cell days compared to non-cold-frontal cell days. Using the 700hPa level as a reference point we show the maximum cell frequency is 350–400km ahead of the 700hPa frontal line which is marginally ahead of the mean surface front location and maximum in surface convergence. The 700hPa front location marks the minimum in the cell frequency and a clear shift in regime between cells with a weakened diurnal cycle on the warm-side of the 700hPa cold front and strongly diurnally driven cells on the cold-side. High cell frequencies are found several hundreds of kilometres ahead of the surface front and cells in this region are most likely to be associated with mesocyclones, intense convective cores and lightning where CAPE is climatologically higher.

How to cite: Pacey, G., Pfahl, S., Schielicke, L., and Wapler, K.: The climatology and nature of warm-season convective cells in cold-frontal environments over Germany, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-120, https://doi.org/10.5194/ecss2023-120, 2023.

P42

ECSS2023-144

Influence of orography on supercells in Slovakia

Miroslav Šinger

The spatial distribution of supercells is strongly inhomogeneous across Slovakia with a higher frequency of occurrence in several regions in the eastern part of the country. The main aim of the work was to find reasons for this inhomogeneity. This is done by running high-resolution simulations of the ALARO model with a grid spacing of 1 km for all supercell cases in eastern Slovakia between 2017 and 2020. We studied the evolution of pre-convective environments, as well as the lower tropospheric flow patterns to establish the typical scenarios, in which supercells occur in Slovakia. The most important factor was found to be an interaction of large-scale flow with local orography, which affected a whole range of processes in the troposphere. As a result of the various orographic effects, such as blocking, wrapping, gap wind, lee cyclogenesis, and upslope flow, we have detected zones of enhanced convergence and spatial anomalies of ingredients important for the development of deep moist convection. In most of the analyzed cases, we noted a local increase in the vertical wind shear in the lee of the mountains, which increased the probability of supercell formation. In the cases with the prevailing southerly flow and warm-air advection regime, supercells typically formed to the south and east of the Western Carpathians. Convergence lines and upslope flow initiated convection and local enhancement of vertical wind shear was essential for the genesis of supercells. In the cases with the prevailing northerly flow and cold-air advection, blocking allowed for the maintenance of a warm and humid air mass (with non-zero CAPE values) and a generation of convergence zone on the southern flank of Western Carpathians.

How to cite: Šinger, M.: Influence of orography on supercells in Slovakia, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-144, https://doi.org/10.5194/ecss2023-144, 2023.

P43

ECSS2023-153

A-5-year climatology of squall from Moldova meteorological stations

Daniela Pruteanu, Gina Tiron, Carleta-Elena Pasat, and Carolina-Irina Oprea

Thunderstorms bring severe weather conditions such as damaging winds, a large hail and heavy precipitation. The squall phenomenon reported at the meteorological station is characterized by a strong variation of wind: its speed increases suddenly for a short period of time, sometimes of the order of minutes, just as quickly accompanied by a change of direction, in most cases. The squall precedes or accompanies Cumulonimbus clouds and it is part of the entire range of sudden variations of meteorological elements that can be observed during the passage of a strong thunderstorm. At synoptic and mesoscale this strong thunderstorm are parts of squall lines. Squall line is a quasi-linear convective system that often occur along a cold front or in the warm sector of a midlatitude cyclone, usually about a few kilometers in advance of the cold front.

This study focuses on a 5-year period between 2018 and 2022 to quantify the spatial and temporal characteristics of squalls, as well as the type of thunderstorm associated with them. We used a set of 100 meteorological observations recorded at the following stations: Galati, Focşani, Tecuci, Barlad, Vaslui, Negresti, Iasi, Cotnari, Botosani, Darabani, Suceava, Piatra Neamt, Bacau and Targu Ocna. These meteorological stations are part of Moldova meteorological network. Radar data from the Barnova meteorological radar were used for the purpose of identifying different types of convective organization, in special squall lines and bow echoes.

Keywords: thunderstorm, squall

How to cite: Pruteanu, D., Tiron, G., Pasat, C.-E., and Oprea, C.-I.: A-5-year climatology of squall from Moldova meteorological stations, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-153, https://doi.org/10.5194/ecss2023-153, 2023.