Hail Days Research Articles

Development and application of a logistic model to estimate the past and future hail potential in Germany

AbstractThis study investigates to what extent the frequency of hail events in the summer months has changed during the past decades and which changes are expected to occur in the future. To improve the diagnostics of hail events by considering various factors relevant for the formation of hail, a logistic hail model has been developed by means of a multivariate analysis method. This statistical model is based on a combination of appropriate meteorological parameters (convective parameter, moisture content, etc.) and synoptic weather types. The output of the model is a new index that estimates the potential of the atmosphere for hailstorm development, referred to as potential hail index. Validations with independent data sets confirm the reliability of the model results. For Germany, the logistic hail model applied to reanalysis data over the past decades shows a markedly north‐to‐south gradient with most of the potential hail days occurring in the south. Applied to an ensemble of seven regional climate model simulations, it is found that the potential for hail events will increase in the future (2021–2050) compared to the past (1971–2000), but only statistically significant in the northwest and south of Germany.

Intraseasonal Variability of Hail in the Contiguous United States: Relationship to the Madden–Julian Oscillation

Abstract Climatologies have been developed to highlight variability of the frequency and intensity of hail in the United States. However, the intraseasonal variability of hail, including why one week might be active while the following inactive despite both having similar climatological probabilities, has not yet been explored. This paper presents relationships between spring-season (April–June) hail days and the leading mode of atmospheric intraseasonal variability, the Madden–Julian oscillation (MJO). It extends recent work on intraseasonal tornado variability to smaller spatial scales. In April, May, and June, statistically significant variability in hail days was found for different Real-time Multivariate MJO (RMM) phases of the MJO. For April, the strongest correlations between hail-day anomalies and anomalies of the product of convective available potential energy (CAPE) and 0–6-km vertical wind shear were found in RMM phase 5, with above-normal likelihood of a hail day found in the south-central United States. For May, the strongest correlations were found in RMM phase 3, with below-normal likelihood of a hail day located over the north-central United States. For June, the strongest correlations were found in phase 8, with above-normal likelihood of hail in west Texas and below-normal likelihood of hail over much of the middle of the United States. In all phases, 300-hPa height anomalies in the United States formed part of a global wave train similar to MJO patterns in both modeling and observational studies.

Hailfall in southwest France: Relationship with precipitation, trends and wavelet analysis

Precipitation in southwestern France was analyzed. Monthly rainfall data from the Global Precipitation Climatology Centre (GPCC) were used to obtain three clusters of average precipitation from May through September for the period 1901–2010. We attempt to understand the role of hailfalls in total precipitation using three different variables related to hail, the number of hail days, hail frequency, and intensity. We examine trends via the Mann–Kendall test and periodicities by wavelet analysis. The results show cluster classification of precipitation to be somewhat consistent with hailpad networks in the study area. In the Pyrenees, there was a non-significant negative trend of precipitation and a substantial increase of hail days and intensity of hail, which were close to the limit of significance. Finally, a wavelet coherence analysis shows a strong influence of the North Atlantic Oscillation (NAO) in the Atlantic region.

Change in hailstone size distributions with an increase in the melting level height

In France, the melting level height varies, during the hail season, from about 1km in the spring to more than 4km in the summer, and this parameter appears to have a connection with the mean characteristics of hailfalls. In fact, a large 25-year sample of hail size distribution measurements, made with hailpad networks along the southern Atlantic coast, reveals strong correlations between the melting level height and the mean hailstone number in different hailstone diameter ranges. On average, an increase in the melting level height is associated with a decrease in the number of small hailstones (5 to 7mm diameter), has no apparent effect in the middle range (7 to 9mm), and is concomitant with an increase in the number of larger hailstones, particularly in the 11 to 21mm ranges. When the relationships giving the hailstone number in each diameter range as a function of the melting level height are applied to a given hailfall, an increase in the melting level height is then found to go together with changes in the total hailstone number and kinetic energy. From this observation, it is possible to estimate the potential effect of global warming on hailfalls with different hailstone size distributions. The trends in the monthly surface temperature and in the hail day melting level height observed at Bordeaux during the 1988–2012 period and the global warming projections made for the present century suggest that an increase in the melting level height of 500m is forecast to occur in this region between 2000 and 2040. The consequences of such an increase for a standard hailfall in the region will be a slight decrease (−12%) in the total number of hailstones, and a significant increase (40%) in total kinetic energy, but with no significant change in the hail frequency. This analysis is compared to the already observed increase in hail intensity in the area under study, and to observations, measurements, and numerical models in other parts of the world.

河北省南部强对流天气的时空分布及对流参数统计特征

利用河北南部石家庄、邢台、邯郸三个地区50个县(市)气象站1999~2008年10年的雷暴、大风、冰雹和暴雨等观测资料以及由MICAPS3探空资料导出的同期对流参数，对这一区域强对流天气事件的时空变化特征及相应对流参数的统计特征进行了分析总结。结果表明，1999~2008期间河北南部年平均雷暴日数为74.8 d，其中雷暴大风有28.2 d，冰雹有9.4 d，暴雨天气有12.3 d；10年中1、2和12月份均未出现强对流天气，雷暴和暴雨天气最多出现在7月份，而雷暴大风和冰雹天气则最多出现在6月份；一般而言，午后到傍晚为强对流天气的高发时段。研究区域西部的雷暴和冰雹天气明显多于东部，雷暴大风多见于中部的平原上，而西北和东南部则是暴雨的高发区。表征对流的参数中，热力能量类参数，如总指数TT、K指数、T850~500和对流有效位能CAPE等，总是在强对流天气出现的时候取值更大，但暴雨的T850~500取值却明显较小，表明垂直方向上温度的强梯度不是发生对流性暴雨的必要条件；表征强对流天气的动力参数——强天气威胁指数(SWEAT)在强对流事件中均表现为较高的数值，瑞士雷暴(SWISS)指数则相反，取值明显较低，进一步分析表明动力类对流参数可被用作强对流潜势预报的参考指标；表征层结稳定度的参数——沙氏指数较小(SI ≤ 1)、θse850~500较大(≥5)是强对流天气比较显著的特征；对流凝结高度(CCL)在雷暴、冰雹和暴雨事件中取值较低，在雷暴大风事件中则取值较高。不同月份强对流天气的对流参数对比，7月份的对流参数大多表现出强于其它月份的特征。 Using the observational thunderstorm, thunderstorm gale, hail and rainstorm data at 50 meteorological sta-tions in Xingtai, Shijiazhuang, Handan Districts of Hebei Province, China, and the convection parameters drawn from the MICAPS3 system during 1999-2008, spatial and temporal distributions of the severe convective events and several convective parameters have been analyzed. It has been shown that, on average, there are 74.8 thunderstorm days in a year over South Hebei, including 28.2 thunderstorm gale days, 9.4 hail days, and 12.3 rainstorm days. Strong convec-tive weather does not appear in January, February and December. Most thunderstorm and heavy rain events appear in July, and most thunderstorm gale and hail appear in June. Strong convective weather usually occurs in the afternoon. Apparently, compared to the eastern part, more thunderstorm and hail events appear in the western region of the study area. Thunderstorm gales often appear in the central part, and the heavy rain events in the northwestern and southeastern parts. For the strong convective weather, the thermal and energy convection parameters, such as TT, K, T850~500 and CAPE, are all numerically higher. But the parameter of T850~500 for rainstorm is relatively small, indicating that the rain-storm occurrence is not caused by any strong vertical temperature variation. The dynamical parameter of the strong weather threaten index is always showing a larger value, but the Switzerland thunderstorm index always appears to be smaller, indicating those power parameters may be used as reference indexes to forecast strong convection potential. The small SI stability index (no larger than 1) and large θse850~500 (no less than 5) can always characterize the strong convection events. In addition, the convection-condensation height is lower, that is, the CCL value is larger for thunder-storm, hail and heavy rain events, but higher for thunderstorm gales. The heights where the temperature reaches 0 and −20 Degrees Celsius can be regarded as characterized heights for hail. The parameters show that convection seems to be stronger in July than in other months.

Extreme hail day climatology in Southwestern France

The concentration of hail damage over a very few days of each warm season is a main characteristic of hail climatology in Southwestern France. The hailpad networks set up there in 1988 by the ANELFA hail prevention project have allowed the development of a new extreme hail day climatology which consists in examining the hail day data in the Atlantic region mainly under maritime conditions, and in the Pyrenean region, under continental and mountain influences. A pyramidal representation of each daily mean hailfall parameter (frequency per station, kinetic energy per hailfall, and kinetic energy per station), ranked by order of magnitude, allows a comparison of the mean and extreme values in the two regions, and reveals the strongest hail days in each one. During the 23-year period under study, 13 extreme situations (7 in the Atlantic region, 6 in the Pyrenean one) are highlighted, keeping the first three day ranking for each parameter. For each day, the synoptic situation, cell type, storm trajectories, and hail damages are examined, and numerical simulations with the WRF model, initialized by the CDAS/NCEP-NCAR reanalysis program, are considered.The study confirms that the Pyrenean region (20,000km2) has experienced the major hail situations, with record values of each parameter for the two regions. On the frequency record day (16 April 2007), 17% of the hailpad stations were impacted, and on the kinetic energy record day (16 July 2009), the total hailstone energy reached 33J/m2 per station. Two main types of synoptic situations have been identified according to the location of the pressure low generating the upper level flow, either near Portugal or near Ireland. A third type, with the pressure low above the Mediterranean, has been observed only once. The WRF-NMM simulations show that all the severe hailstorms that occurred in the twelve situations (one situation is common to both regions) developed in the areas where the mesoscale environment was characterized by a strong dynamical forcing and by high values of the low-level and deep shears. After calibration with this sample of extreme hail days, the WRF model appears promising for severe hail forecasting.

Long‐term trends of hail‐related weather types in an ensemble of regional climate models using a Bayesian approach

This paper investigates the long‐term variability of specific weather types that are associated with damaging hailstorms in Germany for past (1971–2000) and future (2011–2050) time periods. Forty large‐scale weather types are determined by the objective weather type classification scheme of German Weather Service. This scheme is applied to both reanalyses (ERA‐40) and eight different regional climate model (RCM) simulations. It is shown that the RCMs are able to approximately reproduce the distribution of weather type occurrences obtained from the reference of ERA‐40. Using additional insurance loss data, the weather types are further identified as hail‐related or hail‐unrelated. Hailstorms are neither captured comprehensively by existing observation systems nor can they be modeled reliably and the large‐scale weather types are here considered as proxies for hail occurrence. Four weather types that are most likely associated with damaging hailstorms show a slight increase both during the past and future period according to the RCM simulations. A novel statistical model is developed for the probabilistic prediction of the fraction of hail damage days conditional on the weather types. The model is Bayesian and uses a Markov Chain Monte Carlo approach. For the ERA‐40 reanalysis the model prediction agrees well with fraction of hail damage days observed in the insurance data. For most of the RCM projections, the statistical model predicts a slight increase in the number of hail days in the future (2031–2045), with relative changes between 7 and 15% compared to the period 1971–2000.

Hail occurrence in Poland

Hail occurrence in Poland The main objective of this study was to present the spatial and temporal distribution of hail in Poland covering the period of 1973-2009. The analysis was based on the data for 23 meteorological stations published by The Institute of Meteorology and Water Management (1973-1980) and National Climatic Data Center (for the years 1981 to 2009). The results are presented with the maps of mean monthly and annual number of hail days, histograms of the seasonal variation of hail and trend lines in temporal variability of hail. It shows that in Poland the mean annual number of hail days varies from 1,3 near Suwałki to 10 near Hel. Most of the hail cases occurred in March, when the number of mean monthly hail days amounted almost 15. When it comes to temporal variability it is characterized by increasing tendency with the maximum at the beginning of 2000.

Influence of hail suppression on the hail trend in Vojvodina, Serbia

The influence of hail suppression by silver iodide seeding on the trend in the number of hail days (the hail trend) in Vojvodina was studied in two cases; (1) from 1967 to 2002 when there was no hail suppression and (2) from 2003 to 2010 when hail suppression existed on the whole territory. The hail trend in Vojvodina was calculated on the basis of all observed data from all synoptic and climatological stations in the period 1967 to 2010. Previous two cases show that the hail trend was increasing when there was hail suppression. Obtained results are not in accordance with the expectation that hail suppression decreases hail in Vojvodina.

Temporal distribution of weather catastrophes in the USA

The temporal distributions of the nation’s four major storm types during 1950–2005 were assessed, including those for thunderstorms, hurricanes, tornadoes, and winter storms. Storms are labeled as catastrophes, defined as events causing $1 million or more in property losses, based on time-adjusted data provided by the insurance industry. Most catastrophic storms occurred in the eastern half of the nation. Analysis of the regional and national storm frequencies revealed there was little time-related relationship between storm types, reflecting how storm types were reported. That is, when tornadoes occurred with thunderstorms, the type producing the greatest losses was the one identified by the insurance industry, not both. Temporal agreement was found in the timing of relatively high incidences of thunderstorms, hurricanes, and winter storms during 2002–2005. This resulted in upward time trends in the national losses of hurricane and thunderstorm catastrophes, The temporal increase in hurricanes is in agreement with upward trends in population density, wealth, and insurance coverage in Gulf and East coastal areas. The upward trends in thunderstorm catastrophes and losses result from increases in heavy rain days, floods, high winds, and hail days, revealing that atmospheric conditions conducive to strong convective activity have been increasing since the 1960s. Tornado catastrophes and their losses peaked in 1966–1973 and had no upward time trend. Temporal variability in tornado catastrophes was large, whereas the variability in hurricane and thunderstorm catastrophes was only moderate, and that for winter storms was low.

Explicit Forecasts of Hail Occurrence and Expected Hail Size Using the GEM–HAILCAST System with a Rainfall Filter

Abstract HAILCAST is a numerical model developed specifically to predict the size of the largest hail reaching the ground. It consists of a steady-state cloud model combined with a time-dependent hailstone growth model. The regional version of the Canadian Global Environmental Multiscale (GEM) model is used to provide prognostic model soundings that are used as input data for HAILCAST. A map of forecasted maximum hail size is thereby obtained. Because hail is typically accompanied by rain, it would be advantageous if the GEM–HAILCAST system were to predict the occurrence of hail only in those regions where the GEM model was predicting precipitation. Hence, the utility of applying a forecast rainfall mask from the GEM model to restrict hail forecasts to those areas where rainfall is forecast during a 12-h window centered on 0000 UTC was tested. The accumulated precipitation filter is objective and integrates both the thermodynamic and dynamic output from the GEM model over many time steps. To test the utility of applying the GEM forecast precipitation mask, the masking technique was applied to HAILCAST-predicted maximum hail size maps for the three Canadian prairie provinces between 1 June and 31 August 2000. Several case studies will be presented to illustrate the usefulness of adding the precipitation mask. Verification statistics confirm that applying the rainfall mask tends to slightly reduce the false alarm ratio while still identifying the majority of hail events within a special study area over southern Alberta. The performance of the precipitation masking technique was not as effective on severe hail days, especially when attempting to identify both the occurrence and location of severe hail swaths.

Recent trends of thunderstorm and hailstorm frequency and their relation to atmospheric characteristics in southwest Germany

AbstractIn the context of climate change, it is of particular interest whether extreme events connected to severe thunderstorms have been increasing in number or intensity over the past few decades. Due to their small horizontal extent, such events are not entirely and uniquely captured by current observation systems. To obtain comprehensive information about the convective activity in the state of Baden‐Württemberg (southwest Germany), we analysed different datasets for the period 1974–2003. They comprise thunderstorm days detected at synoptic stations, hail damage data from a building insurance company, large‐scale circulation and weather patterns, and convective indices derived from radiosonde observations at 12:00 UTC.While the annual number of thunderstorm days remained almost unchanged in the mean, hail damage and hail days significantly increased in the last three decades. Both damage and additional radar data indicate that the majority of hail days can be attributed to three specific circulation patterns. Two of the three patterns associated with the preferable occurrence of hail show a significant increase.Most of the commonly used convective indices that depend upon surface temperature and moisture reveal a positive trend regarding both the annual extreme values and the number of days above/below specific thresholds. A relationship was established between the indices and the annual number of hail damage days, yielding correlation coefficients between 0.65 and 0.80. In contrast to this, indices derived from temperature and moisture at higher levels exhibit either a negative or no significant trend. It is shown that the trend directions of the indices may be attributed to differential temperature and moisture stratification in the various atmospheric layers. The significant positive trends of both surface temperature and water vapour can be concisely expressed by an increase in wet‐bulb potential temperature. This indicates the presence of warmer parcels throughout the whole troposphere during convection. Copyright © 2009 Royal Meteorological Society

Hail frequency, distribution and intensity in Northern Greece

Hail numerical and physical parameters are examined for an assessment of frequency, spatial and temporal distribution and intensity of hailfalls in Central Macedonia periphery, Northern Greece. Data from weather stations of the Hellenic National Meteorological Service (HNMS) indicated a mean yearly point frequency varying between 1 and 2 hail days for Central Macedonia. Crop insurance data from the Hellenic National Agricultural Insurance Organization (ELGA) showed a mean regional frequency of 22.3 hail days for the total cultivated area of Central Macedonia, about 6,500 km 2, for the warm season, from April to September. Hailpad data representing almost one third of the total cultivated area of Central Macedonia, indicated a regional average of 8 hail days and 45 hailpads recording hail for the warm season. Spatial analysis over the hailpad area revealed a large variability of hail occurrence, with local maxima at the higher altitude and close to mountain barrier areas and a decreasing frequency over areas closer to the sea. The size distribution of a sample of 22,000 hailstones measured by the hailpads, showed a great majority, of 85.7%, having diameters up to 11 mm. An inter-comparison of hail impact energies according to crop damaging potential indicated Central Macedonia hailfalls as the less intense compared to those of areas of Northern America. Application of the revised TORRO hail intensity scale extending to classes from H0 to H10, permitted a classification of Central Macedonia hailfalls appropriate for comparisons and correspondence between areas and countries about the severity and damaging of hailfalls.

Trends in hail in China during 1960–2005

The annual variation and trend in hail frequency during a 46‐yr period from 1960 to 2005 in China are documented in this study. All analyses are based on a comprehensive collection of observational hail data and operational atmospheric sounding data released by the National Meteorological Information Center (NMIC) of China. The results show no trend in the mean Annual Hail Days (AHD) from 1960 to early 1980s but a significant decreasing trend afterwards. The different trend of the AHD at each station displays a marked regional dependence across China, however. Convective Available Potential Energy (CAPE), strength of vertical wind shear, and mean Freezing‐Level Height (FLH) are analyzed to understand the observed long‐term trends in hail frequency.

The Sensitivity of the Northeast Colorado Thunderstorm Environment to Upstream Surface Conditions

Abstract Statistical evidence supports a relationship between the warm-season thermodynamic environment in northeastern Colorado and the antecedent snow conditions in the upstream higher elevations. Above-normal snow storage and longevity reduces the sensible heating of the elevated terrain by increasing the albedo and exerting a stabilizing influence upon the surface layer. It follows that the residual spring snowpack of the Colorado Rockies represents an energy sink to the prevailing west to southwesterly winds of the free atmosphere, which traverse the uplift of the Western Plateau. The abrupt drop in elevation along the Front Range provides for a setting in which a thermal perturbation induced by mountain snow may be communicated to the downstream plains by cooling and perhaps stratifying the mobile elevated residual layer. Statistical and observational evidence suggest that the May and June months that follow a robust and extended snowmelt season are characterized by cooler 700-mb temperatures over Denver, Colorado. The apparent moist convective response to a positive snowmelt anomaly in the lee plains region is for severe weather to develop on average 45 to 50 min earlier, during May and June, than observed during seasons having a negative snow anomaly. Conversely, late springs, which harbor below-average snow, subject the elevated terrain to greater sensible heating. During the May and June months of these “low snow years,” 700-mb environmental conditions over Denver tend to be warmer and drier. Occurring in tandem with these trends are a reduction in May and June rainfall and a lower number of severe hail days on the lee plains. Observations further suggest that during low snow years substantial precipitation deficits extend to synoptic-scale distances downstream.

Spatial Forecasts of Maximum Hail Size Using Prognostic Model Soundings and HAILCAST

Abstract Forecasting the occurrence of hail and the maximum hail size is a challenging problem. This paper investigates the feasibility of producing maps of the forecast maximum hail size over the Canadian prairies using 12-h prognostic soundings from an operational NWP model as input for a numerical hail growth model. Specifically, the Global Environmental Multiscale model run by the Canadian Meteorological Center is used to provide the initial data for the HAILCAST model on a 0.5° × 0.5° grid. Maps depicting maximum hail size for the Canadian prairies are generated for 0000 UTC for each day from 1 June to 31 August 2000. The forecast hail-size maps are compared with radar-derived vertically integrated liquid data over southern Alberta and surface hail reports. Verification statistics suggest that the forecast technique is skillful at identifying the occurrence of a hail day versus no-hail day up to 12 h in advance. The technique is also skillful at predicting the main threat areas. The maximum diameter of the hailstones is generally forecast quite accurately when compared with surface observations. However, the technique displays limited skill when forecasting the distribution of hail on a small spatial scale.

Hailstorms in Northern Greece: synoptic patterns and thermodynamic environment

¶The synoptic scale atmospheric circulation prevailing during hail days in Northern Greece is examined for a period of 26 years (1976–2001) during the warm season. The initial objective of this classification scheme is to serve as a predictive tool for hail forecasting and permit a specification of greater or lesser hail risk, within the forecast activities of the Greek National Hail Suppression Program. The atmospheric circulation was classified into seven synoptic types and their frequency distribution was examined on an annual and monthly basis. Southwesterly flow (SW) and Shortwave trough (SWT) appear to be the most conducive synoptic types for hailstorm activity. Furthermore, the thermodynamic environment favoring the hailstorm development and evolution was examined using selected instability indices. The frequency distribution of the instability indices for a period of 11 years (1991–2001) in association with the synoptic types demonstrated their performance as a forecasting aid for thunderstorm activity to occur in a given synoptic environment.

The climatology of hail in the plain of Friuli Venezia Giulia

Hail is quite common on the plain of Friuli Venezia Giulia (FVG), for this reason a network of polystyrene hailpads was established in 1988. This network remains active today monitoring hail frequency and aspect. We use the data of this network to define the hail climatology for Friuli Venezia Giulia, in particular, its spatial and temporal frequency, and to give a physical interpretation of the observed behavior. The main features that emerge from the analysis are that, even if hail is a local phenomenon, its climatology can be interpreted only by accounting for the mesoscale mechanisms triggered by the interplay between synoptic perturbations and the complex orography of Friuli Venezia Giulia. The analysis also reveals the importance of the lower level (say below 1500 m) water vapor amount for the occurrence of hail. The yearly frequency of hail days in Friuli was also compared with that of other regions and Countries, as well as with the time series of the North Atlantic Oscillation index. The results reveal some significant, even if weak, connections.

Noteworthy C-band radar parameters of storms on hail days in northwestern Spain

The data provided by a meteorological C-band radar have been employed in order to analyze the behavior of 224 storms that occurred on hail days in the provinces of León and Zamora, in the northwest of Spain. A network of more than 700 voluntary observers supplied the necessary information to distinguish hailstorms from storms that did not produce hail precipitation. The observers also reported the size of the hailstones found. Among the variables studied are the maximum reflectivity factors, the vertical developments, and the motion speed of the storm for hailstorms as well as for storms with no hail. The altitude at which the precipitation processes take place inside the storm cell and its average lifetime are the variables that determine the subsequent evolution of hailstorms and no-hail storms in the same day. Furthermore, these variables have been analyzed taking into account the type of storm: unicellular, multicellular or supercellular. Finally, a correlation between the characteristics of the storms and the size of the hailstones registered simultaneously on the ground has been searched for using the RHI detected on the radar exactly at the time of the precipitation.

A Method for Estimating Crop Losses from Hail in Uninsured Periods and Regions

Abstract The insurance industry, insurance regulatory bodies, and scientists investigating climate change all desire long records of hail losses. Existing loss records for some states cover the 1948–present period; this span is helpful but is not long enough to define trends, possible fluctuations, and extremes adequately. The only other hail data with much longer records are the frequencies of hail days collected at National Weather Service stations since 1901, and a newly developed database for the major hail-loss states that contains hail-day data for 910 cooperative stations for 1901–94. This study tested two methods for estimating the historical loss values using hail-day data; one method produced modified hail-day values found to relate closely to loss values in the nation’s 21 primary hail-loss states. The method involved modifying a station’s hail-day values for each of the crop-season months using insurance-derived monthly hail intensity indices, resulting in an annual hail-intensity-weighted val...