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Abstract The Price-Rind 92 parameterization (Price and Rind, 1992) that utilizes cloud top height as predictor for the estimation of lightning density is widely used by modelers in an attempt to forecast electrical activity in thunderstorms. In the present paper new parameterizations for the estimation of lightning density of convective clouds are formulated. LINET lightning data, NWC SAF (Satellite Application Facility on support to Nowcasting and Very Short-Range Forecasting) products and ERA-Interim (ECMWF-Re Analysis) data, covering the summer of 2016 over continental Europe, are used. The proposed models estimate the lightning density of convective clouds, using cloud top height, cloud top pressure and cold cloud depth as predictors. Model efficiency statistics calculated over an independent dataset, suggest that the proposed models can be considered successful over the specific area (continental Europe) and period (summer). The new cloud top height model differs from the PR92 and other parameterizations, which is not an unexpected result, since every model has its own characteristics, strengths and weaknesses. The new parameterizations could be utilized in numerical model simulations to produce quantitative estimations of the amount of strokes over convective areas. Highlights • LINET VLF/LF lightning data, NWC SAF products, and ERA-interim data are used. • The cloud top height/pressure and cold cloud depth relationship to lightning during summer over central Europe is examined. • Uncertainties of the observational data are considered in the modeling process using the Generalized Least Squares technique. • The cross-validation of these models against the control dataset yield low RMSE values, suggesting successful fits. [ABSTRACT FROM AUTHOR]

Abstract: A climatology of various parameters associated with severe convective storms has been constructed for Europe. This involves using the reanalysis data base from ERA-40 for the period 1971–2000 and calculating monthly means, variability range and extremes occurrence of fields such as convective available potential energy, convective inhibition energy, mid-tropospheric lapse rate, low-tropospheric moisture content and storm relative helicity for different layers. This process is a first step towards development of a synthetic climatology of European severe weather, and is publicly available at the web site http://ecss.uib.es. Preliminary results derived from these products were presented during the ECSS 2004 conference. This paper is devoted to a more detailed presentation and discussion of the main results. It is hypothesized that preferred areas for severe thunderstorms occurrence in Europe would extend along a zonal belt over the south-central regions, where high helicity associated with the extratropical storm tracks and thermodynamically-favourable profiles established over the southern Atlantic and Mediterranean Sea would most likely be concatenated. Further, this effort has been complemented with a collection of existing reports of significant (at least F2) tornadoes in Europe during the period 1971–2003. We present this data set in this paper and it also can be found at the website http://ecss.uib.es. Thus, the tornado collection can be used to test the appropriateness of the parameters selected for the synthetic climatology. In particular, it is found that the convective available potential energy, low-tropospheric moisture content and environmental shear, when related to the monthly climatology, are reasonably good descriptors of the tornadic environments. [Copyright &y& Elsevier]

This paper analyses the dependency of regional air pollution in Europe on the atmospheric circulation as represented by a set of 8 weather regimes (WRs). For this purpose, daily average PM 2.5 concentrations and daily maximum concentrations of O 3 , NO 2 and CO obtained from an atmospheric composition reanalysis have been used. The results indicate that the pollutant concentrations change substantially with the occurrence of each WR according to the associated circulation patterns. In the extended winter, the responses of PM 2.5 , NO 2 and CO are quite similar, with zonal circulation regimes leading to better air quality than anticyclonic regimes linked to steady flows over Europe. On the other hand, the spatial patterns of O 3 anomalies under most WRs resemble those of temperature in the extended summer as temperature enhancements favour the photochemical production of O 3. The WR characterized by anticyclonic anomalies over Scandinavia leads to the highest concentrations at continental scale and is concurrent with an increased probability of exceeding the poor air quality limits of winter PM 2.5 and summer O 3 in most European countries. It is also found that a multiple linear regression model on the monthly frequency of WRs can explain a considerable fraction of the intermonthly variability of concentration anomalies over large parts of Europe regardless of the pollutant, with R2 values around 0.6–0.8 over large regions. Overall, the application of these models to sub-seasonal weather forecasts does not seem to bring major improvements to the prediction of month-ahead concentration anomalies as compared to the climatology. The poor skill of sub-seasonal forecasts in predicting the WRs for lead times beyond 15 days limits the forecast capability. However, these results open the possibility of extending current air quality forecast to scales of 5–10 days at a low cost in a near future. [Display omitted] • European-wide study of the modulation of air quality by weather regimes (WRs). • WRs explain 60–80% of the monthly variability in air pollution over large regions. • The poorest air quality in most of Europe is associated with Scandinavian blocking. • Evaluation of WRs as a tool to predict month-ahead air pollution anomalies. [ABSTRACT FROM AUTHOR]

Abstract: Forecasting hailstorms is an important challenge. Improving these forecasts is of vital importance to reduce the risks that this phenomenon causes to the environment and the population. This paper presents a methodology for the characterization of hailstorms in different scales by means of: the definition of the synoptic environment favorable to convection, the establishment of mesoscale configurations on hailstorm days, and an analysis of prediction parameters for the presence of hail. Simulations with the WRF model were done for 100 study days in which hailstorms were produced in the Middle Ebro Valley. The synoptic environment was defined from the average geopotential and temperature fields at 500hPa. Using multivariate techniques of the Principal Component Analysis in T-Mode and a Cluster Analysis, four mesoscale configurations were defined for the fields of convective instability, water vapor flux divergence and wind flow and humidity at low layers. Finally, the study included several hail forecast parameters: CAPE, Storm Relative Helicity between 0 and 3km (SRH0–3), Energy–Helicity Index (EHI) and Showalter Index (SI); making a comparison between hail/hail-free grid points, which allowed us to determine their values and thresholds in order to discern the presence of hail within convective precipitation areas. The analysis, along with these three basic ingredients, provides a very useful tool that allows for a good approximation for predicting storms with hail in the study area. [Copyright &y& Elsevier]

Abstract: Documentary evidence is employed to present the history of tornadoes in the Czech Lands (recently Czech Republic) in AD 1119–2010. Based on contemporaneous descriptions of events, tornadoes are categorised as proven or probable. They are analysed collectively in terms of their spatio-temporal changes, annual variation, specific features, and impacts according to the Enhanced Fujita (EF) scale. The first documented tornado, on 30 July 1119, did great damage to Vyšehrad Castle in Prague (EF3). Only three other tornadoes were recorded before AD 1500. In the following three centuries, the number fluctuated between 11 and 16 events per century. Documented tornado frequency increased significantly from the 19th century onwards, reaching peaks in 1931–1940 (44 tornadoes) and particularly in 2001–2010 (56 tornadoes); this rise, however, reflects the availability of relevant sources as well as increased social awareness and advances in communication technology. A total of 264 tornado days and 307 tornadoes were documented for the Czech Lands in 1119–2010. Although they are relatively homogeneously extended over the territory of the Czech Republic, tornadoes tend to occur more frequently at lower and medium altitudes. The highest frequency of tornadoes is recorded for the summer half-year (mainly from June to August), although they may develop between March and October. Probable tornadoes have also been recorded in the winter months. The strongest tornadoes in the Czech Lands may be classified as EF3, largely with significant damage to buildings and trees, but 13 related deaths have also been recorded. The paper presents not only a new chronology and climatology for Czech tornadoes but is also an important contribution to the study of tornadoes in Europe. [Copyright &y& Elsevier]

Abstract: This purposes of this paper are to: 1) demonstrate an objective overshooting top (OT) detection method using Meteosat Second Generation (MSG) Spinning Enhanced Visible and Infrared Imager (SEVIRI) infrared data, 2) produce an OT database for all operational SEVIRI data over Europe and north Africa for the six Northern Hemisphere warm seasons observed by SEVIRI to date, and 3) determine the frequency of OT detections in the vicinity of confirmed severe weather reports recorded within the European Severe Weather Database (ESWD). Algorithm performance is demonstrated for a case where numerous severe storms were present. Qualitative comparisons indicate that most OT detections correspond with the characteristic OT signature in SEVIRI 1km resolution visible channel imagery, but some OTs were left undetected due in part to relatively coarse SEVIRI spatial resolution over the European domain. The SEVIRI OT database shows a strong relationship between OT maxima and regions with high terrain. OTs are found to occur more frequently during the day over land and during the night over water. Inter- and intra-seasonal variability in OT frequency and location are also shown. An OT was found near 47% of the confirmed ESWD events. The OT–severe weather relationship is strong for large hail (53%) and severe wind (52%) events but relatively weak for tornado events (14%). The weak OT–tornado relationship may be related two factors: 1) low-level wind shear is found to be of greater importance than large CAPE and strong updrafts (i.e. OTs) in tornadic storm environments across Europe and 2) a weakening of the storm updraft and collapse of the OT region has been documented prior to tornado formation. The relatively strong overall OT–severe weather relationship suggests that OT detections can be used to increase forecaster confidence that a given storm is severe, especially in regions where frequent, ground based Doppler weather radar data is unavailable. [ABSTRACT FROM AUTHOR]

Abstract: This paper is devoted to a case study of one of the best-known historical severe storms in Europe. Organised convective systems with the characteristic behaviour of a supercell storm evolved in a meso-α scale convective complex, and the locally damaging weather affected a strip of land from Switzerland to Poland. The development of the storm resulted from a specific combination of processes at various spatial and temporal scales. This study focuses on an analysis of the synoptic and sub-synoptic meteorological conditions before and during the event. The re-analyses ERA-40 are used to investigate anomalies of dynamic and thermodynamic quantities at the synoptic scale. It is demonstrated that some quantities may reach abnormal values not only during large-scale precipitation events, but also during a case of severe convection. The non-hydrostatic limited-area NWP model COSMO is employed to re-forecast the event and to investigate the specific features of the convection environment with a horizontal resolution of 2.8 km. The skill of the re-forecast of precipitation is evaluated using verification methods based on selected categorical skill scores and area-related root mean square error values. Simulated precipitation and radar data show good agreement with observations in terms of daily totals and the spatio-temporal evolution of the storm. The outputs from the diagnostic Model for the Objective Analysis of Gust Fronts indicate that the simulated convection environment does not differ significantly from the real conditions. In addition, the analysis reveals vertical shear and stability conditions favourable for the intensification of convective processes by propagating gust fronts in the areas where new convection formed. [Copyright &y& Elsevier]

It is well known that the United States has the greatest number of severe thunderstorms and tornadoes of any nation worldwide. Therefore, in the United States, a substantial infrastructure has evolved in response to the numerous natural hazards (not limited to severe thunderstorms and tornadoes) in an effort to reduce the societal impacts of these hazards. In addition to keeping records of the events, there are state and national programs (public and private) to help reduce the economic and social impacts on local communities that might otherwise have to prepare for severe storms and rebuild using only the limited local resources. This paper reviews the basics of the infrastructure that has been developed to deal with severe thunderstorms and tornadoes, and describes its history briefly, as well as considering some of its successes and problems.Although the American system should not be used as a simple template for Europe, it does need to be considered as Europe begins to address how to deal with the unique character of European severe storm hazards. Given that severe thunderstorm and tornado event frequencies are generally lower in Europe, as well as the smaller areas of individual European nations, each country has a correspondingly low annual event frequency, especially for the rare “high end” events that have the potential create major disasters. Collectively, however, the severe weather threat is almost certainly larger for Europe as a whole than most Europeans realize. Any decision concerning the phenomena that will be considered “severe weather” in Europe needs to be made in a purely European context. It is suggested that severe weather is best dealt with as the pan-European hazard it truly represents. Pan-European severe weather forecasting and research centers are proposed and issues that will need to be confronted are reviewed. [Copyright &y& Elsevier]

Different air stagnation indices (ASIs) have been proposed to measure the atmospheric diffusion conditions. This paper undertakes a comparative analysis of three ASIs and explores their ability to capture the conditions conducive to elevated PM 10 (particulate matter ≤10 μm) at 306 background sites in Europe for the winter and summer months of 2000–2012. Despite the similar spatial patterns of stagnation frequency found for the three ASIs, the use of different meteorological variables to characterize the dilution capacity of the atmosphere (wind speeds at 10 m and 500 hPa, boundary layer height and ventilation in the boundary layer) leads to important differences in the seasonal cycles. Moreover, the response of the PM 10 concentrations to stagnation varies with the ASI. Winter PM 10 anomalies under stagnant conditions are of the same order of magnitude (on average 17.2 to 18.6 μg m−3, around 60% of the mean values) for the three ASIs. The anomalies are considerably smaller (3.8–5.7 μg m−3, around 19–28%) in summer, when one of the indices outperforms the others at most locations. The dependence of the PM 10 concentrations on the ASI components is also evaluated by using correlations and generalized additive models. The results indicate that the consideration of the large-scale circulation is particularly relevant in summer, explaining the different ASI performances during this season. We have also identified some potential improvements that could be made to two of the ASIs. Nevertheless, since the three ASIs are based on fixed thresholds, they cannot deal with non-linear relationships, which limits their ability to explain PM 10 variability. • First comparison of three different air stagnation indices in Europe. • The indices yield different seasonal cycles in the frequency of air stagnation. • The response of PM 10 to stagnation varies with the index, location and season. • Large-scale circulation consistently contributes to reproducing PM 10 variability. • Fixed thresholds limit the ability of stagnation indices to explain PM 10 variability. [ABSTRACT FROM AUTHOR]