Tomas Pucik - Academia.edu (original) (raw)

Papers by Tomas Pucik

The European Storm Forecast Experiment (ESTOFEX) is a team of volunteer forecast... more The European Storm Forecast Experiment (ESTOFEX) is a team of volunteer forecasters that have been providing experimental convective outlooks for Europe since 2002. Probabilistic storm forecasts issued by ESTOFEX address threats posed by severe convective storms, i.e. lightning, large hail, severe wind gusts, tornadoes and excessive precipitation. ESTOFEX also serves as a platform for exchange of knowledge about forecasting severe convective storms with a goal of improving their understanding among both members of ESTOFEX and others. While not official, ESTOFEX products have been widely used by national meteorological services, severe storm communities and the public. ESTOFEX forecasters have regularly contributed to the ESSL Testbeds and are using an ingredients based forecasting methodology to forecast severe storms. Consistently improving severe storm reporting in the European Severe Weather Database (ESWD) and availability of ground-based lightning detection measurements over the last decade enabled the verification of a large number of ESTOFEX forecasts. Thus, in this work we evaluate 4019 convective outlooks issued by ESTOFEX forecasters since 2007. Our goals are to detect spatiotemporal patterns in convective outlooks and test the reliability of issued threat level polygons, i.e. for a low and high probability of lightning, and an increasing probabilities of severe weather: level 1, level 2 and level 3. We performed the verification by applying a number of methods, including contingency table statistics, receiver operating characteristic curves, practically perfect hindcasts and by calculating spatial coverage of detected lightning (ATDnet network) and local storm reports (ESWD) within issued polygons. Results indicate that products issued by ESTOFEX over the last 15 years, when combined together, are consistent with convective climatologies based on reanalyses and lightning detection data. However, we note that forecasters tend to issue outlooks relatively more often for severe weather outbreaks across western and central Europe. We found that while 95% of the issued lightning probability areas fulfilled the required criterion of coverage, this was only true for 40% of the severe weather probability areas. One reason is that while lightning observations are relatively homogeneous across the forecast domain, the same cannot be said about severe weather observations. These are lacking in regions such as southeastern or eastern Europe, while forecasters calibrated themselves to the higher observed coverage in western and central Europe. The reliability of ESTOFEX forecasts increased over the time, but we found underestimation of lightning probabilities over southern Europe and an overestimation of lightning probabilities over British Isles and Scandinavia.

Weather and Forecasting, Feb 25, 2020

The tornado outbreak of 24-25 June 1967 was the most damaging in the history of western Europe, p... more The tornado outbreak of 24-25 June 1967 was the most damaging in the history of western Europe, producing 7 F2-F5 tornadoes, 232 injuries, and 15 fatalities across France, Belgium, and the Netherlands. Following tornadoes in France on 24 June, the Royal Netherlands Meteorological Institute (KNMI) issued a tornado forecast for 25 June, which became the first ever-and first verified-tornado forecast in Europe. Fifty-two years later, tornadoes are still not usually forecast by most European national meteorological services, and a pan-European counterpart to the NOAA/NWS/Storm Prediction Center (SPC) does not exist to provide convective outlook guidance; yet, tornadoes remain an extant threat. This article asks, ''What would a modern-day forecast of the 24-25 June 1967 outbreak look like?'' To answer this question, a model simulation of the event is used in three ways: 20-km grid-spacing output to produce a SPC-style convective outlook provided by the European Storm Forecast Experiment (ESTOFEX), 800-m grid-spacing output to analyze simulated reflectivity and surface winds in a nowcasting analog, and 800-m grid-spacing output to produce storm-total footprints of updraft helicity maxima to compare to observed tornado tracks. The model simulates a large supercell on 24 June and weaker embedded mesocyclones on 25 June forming along a stationary front, allowing the ESTOFEX outlooks to correctly identify the threat. Updraft helicity footprints indicate multiple mesocyclones on both days within 40-50 km and 3-4 h of observed tornado tracks, demonstrating the ability to hindcast a large European tornado outbreak.

Bulletin of the American Meteorological Society, Dec 1, 2017

This is a preliminary PDF of the author-produced manuscript that has been peer-reviewed and accep... more This is a preliminary PDF of the author-produced manuscript that has been peer-reviewed and accepted for publication. Since it is being posted so soon after acceptance, it has not yet been copyedited, formatted, or processed by AMS Publications. This preliminary version of the manuscript may be downloaded, distributed, and cited, but please be aware that there will be visual differences and possibly some content differences between this version and the final published version.

Monthly Weather Review, Nov 24, 2015

The environments of severe and nonsevere thunderstorms were analyzed using 16 421 proximity sound... more The environments of severe and nonsevere thunderstorms were analyzed using 16 421 proximity soundings from December 2007 to December 2013 taken at 32 central European stations. The soundings were assigned severity categories for the following hazards: hail, wind, tornado, and rain. For each of the soundings, parameters were calculated representing the instability, vertical wind profile, and moisture of the environment. The probability of the various hazards as a function of CAPE and 0-6-km bulk shear (DLS) is quite different for each of the hazards. Large hail is most likely for high CAPE and high DLS, a regime that also supports severe wind events. A second severe wind regime exists for low CAPE and very high DLS. These events are mostly cold season events. Storms with significant tornadoes occur with much higher DLS than storms with weak or no tornadoes, but with similar CAPE. The 0-1-km bulk shear (LLS) does not discriminate better than DLS between weak and significant tornadoes. Heavy rain events occur across a wide range of DLS, but with CAPE above the median for nonsevere thunderstorms and are most likely when both absolute humidity in the boundary layer and relative humidity in the low-to midtroposphere are high. LCL height does not discriminate well between the intensity categories of tornadoes, but higher LCL heights were associated with a higher probability of severe hail. Storm relative helicity shows similar results to DLS, but with more overlap among intensity categories.

Journal of Climate, Dec 1, 2020

In this study we investigate convective environments and their corresponding climatological featu... more In this study we investigate convective environments and their corresponding climatological features over Europe and the United States. For this purpose, National Lightning Detection Network (NLDN) and Arrival Time Difference long-range lightning detection network (ATDnet) data, ERA5 hybrid-sigma levels, and severe weather reports from the European Severe Weather Database (ESWD) and Storm Prediction Center (SPC) Storm Data were combined on a common grid of 0.258 and 1-h steps over the period 1979-2018. The severity of convective hazards increases with increasing instability and wind shear (WMAXSHEAR), but climatological aspects of these features differ over both domains. Environments over the United States are characterized by higher moisture, CAPE, CIN, wind shear, and midtropospheric lapse rates. Conversely, 0-3-km CAPE and low-level lapse rates are higher over Europe. From the climatological perspective severe thunderstorm environments (hours) are around 3-4 times more frequent over the United States with peaks across the Great Plains, Midwest, and Southeast. Over Europe severe environments are the most common over the south with local maxima in northern Italy. Despite having lower CAPE (tail distribution of 3000-4000 J kg 21 compared to 6000-8000 J kg 21 over the United States), thunderstorms over Europe have a higher probability for convective initiation given a favorable environment. Conversely, the lowest probability for initiation is observed over the Great Plains, but, once a thunderstorm develops, the probability that it will become severe is much higher compared to Europe. Prime conditions for severe thunderstorms over the United States are between April and June, typically from 1200 to 2200 central standard time (CST), while across Europe favorable environments are observed from June to August, usually between 1400 and 2100 UTC.

On the 25th of June 2008, severe thunderstorms caused widespread damage and two fatalities in the... more On the 25th of June 2008, severe thunderstorms caused widespread damage and two fatalities in the Czech Republic.

We have developed additive logistic models for the occurrence of lightning, large (≥ 2 cm), and v... more We have developed additive logistic models for the occurrence of lightning, large (≥ 2 cm), and very large (≥ 5 cm) hail to investigate the evolution of these hazards in the past, in the future, and for forecasting applications. The models, trained with lightning observations, hail reports, and predictors from atmospheric reanalysis, assign an hourly probability to any location and time on a 0.25° × 0.25° × 1-hourly grid as a function of reanalysis-derived predictor parameters, selected following an ingredients- based approach. The resulting hail models outperform the Significant Hail Parameter and the simulated climatological spatial distributions and annual cycles of lightning and hail are consistent with observations from storm report databases, radar, and lightning detection data. As a corollary result, CAPE released above the -10°C isotherm was found to be a more universally skilful predictor for large hail than CAPE. In the period 1950–2021, the models applied to the ERA5 rean...

Both 2021 and 2022 broke records in terms of the amount of large (&#8805... more Both 2021 and 2022 broke records in terms of the amount of large (&#8805; 2 cm) and very large (&#8805; 5 cm) hail reports across Europe. 24 June 2021 featured the highest number of large hail reports per day (860) in the history of the European Severe Weather Database and giant (&#8805; 10 cm) hail was reported in three countries. In 2022, the insured damage exceeded &#8364; 4 billion in France alone while 215 people were injured that year. Furthermore, the Catalonian hailstorm on 30 August 2022 caused the first direct hail fatality in Europe since 1997. &#160; In this work, we studied storm-scale processes of severe hailstorms and their larger-scale environment in relation to the maximum observed hail diameter and hailstorm lifetime. The storm-scale properties include storm type, the occurrence of storm mergers, and the type of storm dissipation. &#160;The larger-scale environment was addressed using CAPE-shear parameter space, hodograph properties (shape, longest segment in the hodograph, and storm-relative winds), and the presence of boundaries near the storms. We selected the most impactful hailstorms of 2021 and 2022, all of which featured very large hail and caused considerable damage to property or agriculture, or caused injuries. 79 hailstorms were selected from both years, spanning maximum hail diameters of 5 to 14 cm and hailstorm lifetimes of 10 to 420 minutes. We found that most hailstorm hodographs had a straight shape with the longest segment between 1 and 3 km and storm-relative inflow typically exceeded 10 m/s. Hodograph properties and the amount of CAPE had no relation to the duration of the hailstorm. Hailstorms forming near boundaries had average lifetimes twice as long as hailstorms forming elsewhere. For hail > 5 cm, CAPE had the strongest correlation with the observed diameter, even higher than the CAPE-shear product. Hodographs suggest that the inflow magnitude into the deviant moving storms stays almost the same (around 10 m/s) for 10 to 22 m/s of 0-6 km bulk shear. In some cases, very large hail occurred in marginally favorable environments only after a storm merger occurred. This shows that storm-scale processes (merger, deviant motion of the storm) and interaction with boundaries can be as important as the background environment.

The development of additive logistic regression models (AR-CHaMo) for large hail... more The development of additive logistic regression models (AR-CHaMo) for large hail, severe convective wind gusts, and F1 or stronger tornadoes for Europe and parts of North America allowed us to identify how the best predictors vary among different threats and different forecast domains. The best predictors were identified using the variance explained, based on the skill of logistic models for individual parameters as well as on investigating pairs of different parameters and their relation to hazard frequency. For the models, we have chosen predictors that perform well over both domains and could thus be used to develop a global convective hazard model. In the case of large hail, CAPE was found to be a better predictor across Europe than across North America, where mid-tropospheric lapse rates discriminate better between environments with and without large hail. We found that CAPE below the -10 &#176;C level was a skillful predictor in both domains. For severe convective wind gusts, it was found that they occurred with lower CAPE and lower amounts of absolute moisture in Europe than in North America. Height of the LCL or a parameter that predicts the cold pool strength worked better in Europe than in North America. Strong mean wind in the bottom troposphere was found among the best predictors of severe wind gusts in both domains. Regional differences among the best predictors were also found for F1 and stronger tornadoes, even though the amount of SRH in the lower troposphere is universally a skillful predictor. We applied models using the best predictors of large hail across North America and Europe to the ERA-5 reanalysis to obtain a global model of large hail hazard. Then, we compare the model to existing hail climatologies worldwide and discuss its limitations and potential improvements.

In this work, we use 8 years of OPERA radar data, ESWD severe weather reports, a... more 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%).

The German Meteorological Service (DWD) aims to enhance its ability to provide w... more The German Meteorological Service (DWD) aims to enhance its ability to provide warnings on shorter notice (e.g. of extreme convective events) and therefore implements a rapid update cycle (RUC). This system produces more frequent and faster available numerical ensemble forecasts compared to the standard ICON-D2 short range numerical weather prediction (SRNWP) forecast procedure. The RUC&#8217;s focus is on lead times of up to 12 hours. The RUC&#8217;s capability in predicting extreme convective events is tested by applying its setup to re-forecast the violent tornado case near Hodonin in the Czech Republic in June 2021. As this area is outside of the ICON-D2 domain, the model domain was shifted. While several German radar stations could not contribute to the new domain, 3D radar reflectivities and radial winds from several Czech and Slovakian radars were used for this case study. The assimilation cycle is started from the ICON-EU state the day before the event and hourly ensemble forecasts are started before the actual event. In addition, we included a nested domain, which uses a resolution of ~1km to evaluate the impact on the atmospheric parameters and dynamics. We present results of the simulation of the atmospheric condition as well as tracks and dynamics of the developing convective systems with respect to different lead times and horizontal resolutions. As expected, there is an increase in forecast accuracy of the convective event with decreasing lead time. With respect to the different horizontal resolution, amplitudes of wind speed and updraft helicity are larger for the 1-km domain. Further, the rotation signature of the simulated tornadic supercell (e.g. radial wind) is comparable to the actually observed one.

This study is a first step in deciphering the role that climate change-induced c... more 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. <img src="" alt="" /> 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).

In the afternoon of 24 June 2021, severe hailstorms affected Austria, Czechia, a... more In the afternoon of 24 June 2021, severe hailstorms affected Austria, Czechia, and Poland and an F4 tornado occurred in southeastern Czechia. Along the 27.1 km long path, it damaged 1200 buildings and caused 6 fatalities and more than 280 injuries. The width of the damage path was extreme for European standards, up to 2500 m across. The zone with significant damage of F2 or stronger was up to 520 m wide. Isolated instances of F4 damage were noted in 3 villages with the destruction of well-constructed brick walls and significant debarking of trees. We discuss the challenges associated with surveying the tornado from an organizational point of view to the strategy onsite. Improvements are proposed to make surveys of such large-scale events more effective.The event was not well forecast even by expert forecasters present at the ESSL Testbed 2021. Although the environment was clearly conducive for supercells capable of very large hail with high values of CAPE (> 3000 J/kg) and strong vertical wind shear (0-6 km bulk shear > 20 m/s), lower tropospheric shear was forecast to remain fairly weak by most of the NWP models with 0-1 km bulk shear < 10 m/s and 0-1 km SRH < 100 m2/s2. The fact that only one tornado (and of such a high intensity) occurred in the area despite numerous supercells present points to the importance of mesoscale modifications to the environment. We address the storm-scale evolution starting from the merger of two storms through updraft intensification with giant hail production, and subsequently, low-level mesocyclone strengthening and tornado production. We also discuss the importance of local mesoscale boundaries and modification to the environment shortly before the tornado.The event illustrates a number of difficulties with tornado forecasting in Europe. The first is the lack of sufficient data exchange among countries. The tornado passed within 10 km of the borders of Austria and Slovakia and the tornado-producing supercell formed over Austria. No exchange of automatic station surface observations and volumetric radar data between those countries takes place and this likely limited the situational awareness of forecasters. While the tornado occurred over Czechia, the storm was best detected from a Slovakian radar. Another difficulty was the aggressive filtering of doppler velocity data that masked the core of the low-level mesocyclone preventing forecasters to appreciate the intensity of the event as it unfolded.&#160;

On August 18, 2022, Europe experienced the most severe storm of the year. In the... more On August 18, 2022, Europe experienced the most severe storm of the year. In the early morning, a derecho formed, causing significant damage along a path of over 1000 km as it travelled at an exceptional speed of up to 40 m/s, with wind gusts reaching a maximum of 62.2 m/s. The storm had a widespread impact, affecting Spain, France, Italy, Slovenia, Austria, and the Czech Republic. The severe weather caused fatalities in several countries, with the highest death tolls reported on Corsica and in the Alps. The focus of this analysis is to understand the factors that led to the derecho's exceptional intensity. We examine the storm's chronological development, and the intensification phases it underwent. We also investigate how external and internal forcing contributed to the rapid upscale growth of the storm. From the perspective of external factors, we show the importance of a mid-level front and warm air advection at the lower levels and their relation to the distribution of CIN in the vicinity of the event. We show that the development and movement of convective cells were influenced by the mid-level front. The system was also strongly influenced by the internal forcing as it formed in an environment of high CAPE values and strong low-level vertical wind shear, and intense storm-relative inflow. The combination of internal and external forcing factors eventually resulted in the extreme forward speed of the derecho. Due to the interaction with complex topography, the derecho underwent several weakening and strengthening phases, which we associate with the changes to the internal and external forcing. Finally, we compare the environment of the derecho to typical environments of severe convective wind gusts in Europe and compare the event to similar Mediterranean derecho cases from the past.

This report presents analyses of the probability of hydro-meteorological hazard occurrence, which... more This report presents analyses of the probability of hydro-meteorological hazard occurrence, which were carried out within the RAIN project. Those probabilities and their projected changes during the 21st century are an input to subsequent risk analyses which assist the identification of optimal adaptation measures. The spatial distributions of the probabilities in the present climate were mapped and projections of changes according to the RCP 4.5 and RCP 8.5 climate scenarios were developed. The investigations by the European Severe Storms Laboratory, the Freie Universitat Berlin, the Finnish Meteorological Institute and Delft University of Technology focused on thunderstorm-related phenomena, windstorms and heavy precipitation, winter weather and forest fires, and coastal and river floods, respectively.

We have performed a study of environmental conditions related to severe convective weather using ... more We have performed a study of environmental conditions related to severe convective weather using proximity soundings across central Europe, which, to our knowledge is the largest that has been carried out in Europe to date. Our study was done with forecasters in mind and our aim to help them to assess the risk of particular types of severe weather individually (hail, wind gusts, excessive precipitation, and tornadoes). The full study consists of an analysis of several environmental parameters (indices) and their ability to discriminate between no severe, severe and extremely severe categories that we defined for each severe weather type. The severe weather reports were obtained from ESSL's European Severe Weather Database. The parameters (indices) were calculated from 1962 proximity soundings that were associated with at least two lightning detections by the EUCLID network, acquired for 4 years of thunderstorm activity (2008-2011). Our preliminary results include the following: ...

On this date, an extraordinary severe weather event was observed over the Czech Republic and some... more On this date, an extraordinary severe weather event was observed over the Czech Republic and some other countries (e.g. Germany or Northern Italy) featuring intense hailstorms. In case of the Czech Republic, a single supercellular thunderstorm managed to produce a 230 km long hail swath with many reports of very large hail (up to 12 cm in diameter) and severe wind gusts. This resulted in an extreme damage with some settlements losing every single roof, and also several casualties. Even though a relatively thorough analysis has been done shortly after the event (Pavlik - Kakos - Strachota, 1988), little has been known in those times about the supercell or large hail prediction. Thus, we would like to shed more light on the environmental conditions (using the ingredient-based methodology), which allowed for perhaps the most intense hailstorm in the modern history of the Czech Republic. Large scale conditions will be assessed using the ECMWF reanalysis data with the horizontal resoluti...

An ensemble of 15 EURO-CORDEX model runs was used to investigate the changes in the frequency of ... more An ensemble of 15 EURO-CORDEX model runs was used to investigate the changes in the frequency of severe thunderstorm phenomena (large hail, severe wind gusts and tornadoes) over Europe. For each time frame and grid point, a probability of occurrence was calculated based on the degree of instability, vertical wind shear and the occurrence of precipitation. We show that the local annual probabilities of occurrence are very different for the three investigated phenomena. Future changes were addressed by comparing the RCP4.5 and RCP8.5 simulations to historical (control) runs. Historical runs span the 1971–2000 period, while the future studied periods are 2021–2050 and 2071–2100. The frequencies of all studied phenomena are forecast to increase in the future due to the climate change, especially across south-central Europe. In the RCP8.5 scenario and the 2071–2100 period significant increases are forecast across large parts of Europe. In this case, the frequency of the phenomena increas...

Weather and Forecasting, Feb 25, 2020

Bulletin of the American Meteorological Society, Dec 1, 2017

Monthly Weather Review, Nov 24, 2015

Journal of Climate, Dec 1, 2020