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The onset of periods with very high or low air temperatures has aroused general interest for a long time, which is understandable since it has many dangerous effects directly affecting humans. Such perilous climatic phenomena include exceptionally cold and exceptionally warm months, which this study investigates for all Europe and for its five physico-geographic regions over the 190-year period of 1831-2020. Therefore, the research in this paper includes two periods characteristic of the history of climate - the late Little Ice Age (LIA) and present-day warming. The studies are based on average monthly air temperature values from 40 weather stations in Europe. In this paper, exceptionally cold months (ECMs) or exceptionally warm months (EWMs) are considered to have occurred when the average air temperature at a station differed from the respective long-term average by at least two standard deviations. The highlights of the study include the identification of a drop in the number of ECMs by 20 over the entire 190-year period, and a highly statistically significant increase in EWMs by 44 between 1980 and 2020. These changes proceeded with different intensities from one physico-geographic region of Europe to another.

Contemporary climate warming is a key problem faced not only by scientists, but also all by humanity because, as is shown by the experience of recent years, it has multiple environmental, economic and biometeorological implications. In this paper, the authors identify the magnitude of annual and seasonal temperature changes in Europe and its immediate surroundings on the basis of data from 210 weather stations from 1951 to 2020. An analysis of temperatures in the 70-year period shows that air temperature has continued to grow linearly in Europe since 1985. The rate of temperature rise in three seasons of the year, namely winter, spring and summer, does not differ greatly. The highest growth over the 1985–2020 timespan was recorded in spring and the lowest in autumn—0.061 °C/year and 0.045 °C/year, respectively. In winter, the rise in temperature should be considered the least steady, as opposed to the summer when it displays the greatest stability. Overall, the warming intensifies towards the north-east of the continent. Such a strong gradient of change is especially perceivable in winter and spring, and is also marked in autumn. The opposite is true in summer, when it increases towards the south and south-west.

This study focuses on demonstrating the multiannual patterns of cyclical fluctuations of monthly and annual precipitation in the Polish Carpathian Mountains and their foreland. The study is based on secular series of precipitation totals from 18 meteorological stations for the 138-year period from 1881 to 2018. Use is made of Fourier analysis (FFT) and wavelet transform nonlinear estimation. The study has found a 35-year Bruckner cycle in annual precipitation across the area. The number of days during the year with the types of cyclonic circulation that lead to extremely high precipitation, i.e. with the northerly and north-easterly (Nc + NEc) types and a cyclonic trough (Bc), is not clearly correlated with the 35-year harmonic variability derived from annual precipitation totals. However, the Fourier transform demonstrates a local maximum at T = 35 years. A harmonic 6-month cycle has been discovered as the only harmonic cycle in monthly precipitation. Its stability over the 138-year timespan is investigated.

Extreme climatic phenomena include prolonged heavy precipitation as well as long-lasting absence thereof. They are a consequence of weather anomalies and have many dangerous effects such as floods and droughts. This study aims to characterise the annual and long-term variability of the highest (Pmax) and lowest (Pmin) monthly precipitation totals and their relationship with atmospheric circulation. To achieve the above, use is made of 14 secular series (1881–2018) of precipitation from the Polish Carpathians and the calendar of circulation types over southern Poland prepared by T. Niedźwiedź (1981, 2019). On account of the variation in their relief, the Polish Carpathians are an area with a very great temporal and spatial variability in precipitation, ranging from complete absence to 500 mm per month. Pmax demonstrates a more noticeable annual frequency pattern, with a predominance in summer months, while Pmin shows smaller variations in individual months. Both Pmax and Pmin are characterised by irregular fluctuations in precipitation totals, with no statistically significant trend in their changes, which reflects the absence of a trend as regards overall precipitation volumes in this area. The study confirms an influence of the direction of air mass advection and (anti)cyclonicity of flow on Pmax and Pmin.

The occurrence of long-lasting severe heat stress, such as in July–August 2003, July 2010, or in April–May 2018 has been one of the biggest meteorological threats in Europe in recent years. The paper focuses on the biometeorological and mortality effects of the hot June that was observed in Central Europe in 2019. The basis of the study was hourly and daily Universal Thermal Climate Index (UTCI) values at meteorological stations in Poland for June 2019. The average monthly air temperature and UTCI values from 1951 to 2018 were analysed as background. Grosswetterlagen calendar of atmospheric circulation was used to assess synoptic conditions of heat wave. Several heat strain measures were applied : net heat storage (S), modelled heart rate (HR), sultriness (HSI), and UTCI index. Actual total mortality (TM) and modelled strong heat-related mortality (SHRM) were taken as indicators of biometeorological consequences of the hot June in 2019. The results indicate that prolonged persistence of unusually warm weather in June 2019 was determined by the synoptic conditions occurring over the European region and causing advection of tropical air. They led to the emergence of heat waves causing 10% increase in TM and 5 times bigger SHRM then in preceding 10 years. Such increase in SHRM was an effect of overheating and overload of circulatory system of human organism. Supplementary Information The online version contains supplementary material available at 10.1007/s00484-021-02202-0.

This study determines the frequency, location and spatial extent of such large-area monthly thermal anomalies, which are referred to in this paper as continental-scale thermal anomalies (CTAs). The research was based on monthly mean air temperature values from 210 weather stations over the 68-year period 1951-2018. A CTA is defined as an anomaly when the monthly mean temperature exceeded the long-term average by at least 2 standard deviations at a minimum of 40 stations. This study attempts to explain the occurrence of such CTAs (negative CTAs- and positive CTAs+) in relation to the circulation conditions over Europe. In the years 1951-2018, there were 16 CTAs- (mainly in winter and autumn) and 25 CTAs+ (predominantly in summer). One manifestation of climate warming is the ever less frequent occurrence of CTAs- and a growing frequency and spatial extent of CTAs+. The immediate cause behind CTAs was the occurrence of characteristic synoptic situations, leading to intensified advection of cold or hot air masses, often driven by radiation factors. The formation of CTAs- was much more often associated with very extensive and long-lasting anticyclonic systems, and that the associated synoptic situations over Europe lasted much longer than in the case of CTAs+.

The current climate warming phenomenon manifests itself with the occurrence of, among other characteristics, extremely hot months and seasons. Examples include the heat waves of April and May 2018 and of June 2019, which swept through large areas of Europe with considerable damage to nature and the economy. The study looks at thermal anomalies of this kind using average monthly air temperature records from 210 weather stations collected over the period 1951–2018. For the purpose of the study an anomaly was defined as a deviation of the average monthly temperature from the long-term average by at least two standard deviations. An anomaly was considered large-area if it occurred simultaneously at 20 or more stations, which corresponded to about one-tenth of the continent. The study found that positive large-area anomalies were increasingly frequent, some being recorded at 80 stations, and that no cool large-area anomalies were recorded after 2010. Large-area thermal anomalies of both types were the most frequent overall in Central Europe.

The moderate climate of Poland, transitional between oceanic and continental, is influenced by air masses from all directions – maritime and continental, polar and tropical. Events which have the most negative effect on people and the environment in Poland belong to meteorological hazards (rapid air pressure changes, extreme thermal conditions, droughts) and hydrological hazards (floods). There occur also geological hazard, i.e. landslides, which are closely related to meteorological conditions and radiological hazard of radon which is related to properties of the rocks. The warm half of the year is the most exposed season for natural hazards in Poland. Some of the greatest meteorological threats in Poland include exceptionally heavy or low precipitation, strong winds, violent maritime storms, extreme temperatures. The frequency of occurrence of torrential rainfalls has considerably increased over recent decades. Consequently, increased numbers of local urban floods have been observed. Most severe floods, in terms of flood fatalities and material damage, have occurred in valleys of large rivers (Vistula, Oder) and their tributaries, and particularly in urban agglomerations and industrial areas protected by embankments. The spatial distribution of the occurrence of drought spells in Poland is unfavorable for the country’s agriculture, because a major part of Poland’s agricultural potential is concentrated in regions that are most threatened with the possibility of drought (latitudinal belt in the central Poland). Landslides commonly occur in connection with torrential or long-duration rains or snowmelt, particularly in mountainous areas (Carpathian Mts., Sudety Mts.). Intensified landsliding activity was recorded in the end of 20th and in the beginning of the 21st centuries. The areas most affected by the radiological hazard of radon are the Sudety Mountains and the Fore-Sudetic block (SW part of Poland).

Uwarunkowania cyrkulacyjne temperatury powietrza w Warszawie w miesiącach o skrajnych wartościach wskaźnika NAO (1951–2015)

Extreme thermal conditions appear to occupy an important place among research subjects at a time of climate warming. This study investigates the frequency, duration and spatial extent of thermally anomalous winters in Europe during the 60 years between 1951 and 2010. Exceptionally cold winters (ECWs) and exceptionally mild winters (EMWs) were identified using the statistical criterion of plus/minus two standard deviations from the long-term winter temperature (January–December) recorded at 60 weather stations. It was demonstrated that ECWs have occurred more frequently and covered larger territories than EMWs and that they may occur anywhere in Europe, while EMWs were limited to its southern and western parts. ECWs are characterised by greater absolute temperature anomalies, as anomalies greater than |6.0 °C| account for 35 % of ECWs, but only for 8 % of EMWs. The greatest anomalies are found in the east of the continent. The largest territory affected by an ECW included 24 stations in 1962/1963, while the equivalent among the EMWs included 11 stations in 2006/2007. The study also confirmed an expected trend whereby ECWs diminished in frequency in favour of EMWs in the second half of the 60-year study period.

Based on the monthly precipitation series from 16 sites (in the Polish Carpathian Mountains), of 132 years’ length, a relatively precise scatterplot of correlation coefficients between sites versus distance between sites is obtained. The “rains” of Gaussian shape, in the spatial sense, are a good model, which produces a scatterplot very closely resembling the observed one. The essential parameter of the model is the area covered by the modeled rains, which results to be of order 30–50 km, though with about a twice lower value for the N-S direction.

The paper explores exceptional thermal conditions, an area of research that has increased in significance in the context of the changes that are being observed in climate. Specifically, the study addressed the frequency, long-term change and spatial coverage of exceptionally hot summers, and exceptionally cool summers (EHS and ECS) in Europe. The statistical criterion of plus/minus two standard deviations from the long-term average was used to identify EHS and ECS at 60 weather stations over the period 1951–2010. The study has demonstrated that EHS are characterised by greater temperature anomalies than ECS and are approximately twice as frequent. They occurred virtually everywhere within the study area, whilst ECS are concentrated in its northern part. Five EHS (1972, 2002, 2003, 2007, and 2010) and three ECS (1956, 1962, and 1976) were large enough to be recorded by at least 10% of the stations.

In Europe, the current climate warming manifests itself with an increasing frequency of anomalously warm months (AWMs) and a declining frequency of anomalously cold months (ACMs). For the purpose of the study the authors define thermally anomalous months as months with the average air temperature at least two standard deviations higher or lower (AWM: t ≥ tav. + 2SD, ACM: t≤tav. - 2SD) than the long-term average (1951-2010). The aim of the study is to investigate the frequency of such monthly anomalies in southern Europe (approximately south of 45°N) in the Mediterranean and in Asia Minor (based on records from 80 weather stations), the change in such frequency over the 60-year study period, as well as the location of the anomalies and their coverage area. The number of ACMs and AWMs showed significant variations over the 60-year period.

The paper discusses the frequency, persistence and succession sequence of six types of air mass during the period 1951-2010. The study, which relied on a calendar of air masses in southern Poland published by T. Niedźwiedź, concludes that there is no simple relationship between the persistence and the frequency of specific air masses in the region. The study found that there was a great variety in the persistence of specific types of air mass and that persistence depended more on the direction of air mass advection than on their frequency of occurrence. The study also failed to identify any strict overall rule of succession, as any air mass could follow after any other, but certain finer-grained patterns emerged. In winter and summer, arctic air (A) never followed directly after tropical air (T) or vice versa. Also, the most frequent succession sequence identified was from Polar maritime fresh air (mPf) to Polar maritime old and it accounted for the vast majority of successions from mPf into any other air mass (63 % annually and 76 % in summer).

The paper addresses the frequency, amount and geographic coverage of anomalously heavy precipitation in southern Poland in relation to atmospheric circulation at the monthly and seasonal scales between 1881 and 2010. The Carpathian Mountains and their foreland were selected for the study as an area known for its high precipitation totals and frequent precipitation-triggered natural disasters, such as floods and landslides. Records from 18 stations were used to identify anomalously heavy precipitation (AHP) defined for the purposes of the study, as the top quartile (Q75 %) plus 1.5 times the interquartile gap (H) of the precipitation total (P ≥ Q75 % + 1.5H). The study found that most cases of AHP were recorded at one single station each. This suggests that, in addition, to the influence of circulation, local factors also play a major role in the formation of particularly heavy precipitation. The greatest absolute anomalously high precipitation totals were recorded in two disparate parts of the study area: (i) its western part exposed to wet air masses from over the Atlantic Ocean brought in by the dominant western circulation in the temperate zone and (ii) elevated parts of its south-eastern part. Two months with AHP (AHP months) occurred over the entire area (18 stations) in May 1940 and 2010. The latter case had both the greatest absolute totals (over 500 mm) and relative totals defined as their ratio to the long-term average (500 %), and it triggered a catastrophic flood in the Upper Vistula basin.

The paper discusses the impact of atmospheric circulation on the occurrence of various types of precipitation. A 146-year-long precipitation record from Kraków spanning the period 1863-2008 was used alongside a calendar prepared by Niedźwiedź (1981, 2009) describing circulation types covering the period 1873-2008 and air masses and atmospheric fronts covering the period 1951-2008 in southern Poland. The influence of atmospheric circulation on precipitation was measured using the frequency, conditional probability and average daily totals of precipitation. Circulation types, air masses and atmospheric fronts exerted influences on precipitation as a result of the seasonal variations of the thermal and moisture properties of air masses. The impact is best expressed by circulation types as these combine the aspect of cyclonicity/anticyclonicity with that of the direction of air advection, the two elements which determine the physical properties of the air. On average, liquid precipitation prevailed in all circulation types, except the Ea type in which snowfall dominated over liquid precipitation. Depending on the season, one of the three types of circulation, Wa, Wc and Bc, were shown to coincide with the greatest amount of liquid and thunderstorm precipitation. There was no single dominant circulation type for mixed precipitation or snowfall. In summer, the circulation types Nc, NEc, Cc and Bc were the most favourable to liquid and thunderstorm precipitation in terms of both probability and totals. In winter, snowfall was the most favoured by the Ec type. Frontal precipitation was twice as likely to occur as air mass precipitation, with the exception of snowfall which was predominantly an air mass type of precipitation in terms of probability, but its greatest totals were recorded on atmospheric fronts.

The paper presents parameters of the diurnal rainfall cycle for rainfall equal or exceeding 2.5 mm h −1 during both the summer and winter halves of the year. It then discusses the impact of various circulation systems on the distribution of the frequency of rainfall occurrence during a 24-h day in the summer half of the year. The results of these investigations contribute to a greater understanding of the atmospheric processes associated with heavy precipitation and may be used to improve the forecasting of the temporal distribution of short-duration convective precipitation. A pattern with a single heavy rainfall maximum was identified. A variety of diurnal patterns of amplitude and time of maximum rainfall emerged depending on the atmospheric circulation determining the thermal and humidity properties of air masses. The paper was based on hourly rainfall records in Krakow and on a daily catalogue of atmospheric circulation types in southern Poland spanning the period 1886–2007.

This study was designed to empirically determine what relationships existed between three characteristics of precipitation: maximum depth, duration, and probability of exceedance. Annual maximum series for intervals of between one and 120 h were identified using the 1886-2002 pluviographic record from Krakow. The Gumbel distribution was selected from a group of four of the most popular theoretical maximum value distributions and identified as the optimum solution. Its parameters were determined. Confidence intervals for quantiles were obtained using the bootstrap method. Formulae were derived for the relationships between the Gumbel distribution parameters, i.e., the α location and β scale, depending on precipitation duration. These take the form of a polynomial of the second degree. The model developed was subjected to a two-step validation with a positive result.

This paper describes the diurnal cycle of liquid precipitation using the amplitude and phase of two precipitation characteristics: frequency and totals. A uniquely long set of uniform hourly precipitation data from Krakow (South Poland) was used. This vast and reliable basic material was collected by the author using pluviographic data covering the period 1886–2002. The role of precipitation type in forming the general diurnal cycle of precipitation was discussed. Two precipitation types, frontal and air mass, were taken into consideration. The role of particular air masses (polar maritime and polar continental) and atmospheric fronts (warm and cold fronts) in the 24-h precipitation cycle was determined. The frontal and air mass precipitation events were identified using a documentation of synoptic situations by Niedźwiedź over the area of southern Poland for the 1951–2002 period. Depending on the precipitation characteristic (frequency or totals), season of the year and precipitation type, the diurnal precipitation cycle may have one or two modes. The bimodality of the distribution occurs mainly for air mass precipitation. The morning maximum of precipitation frequency in all seasons of the year mimics the diurnal variation of precipitation in maritime polar air masses. Precipitation concentration in the afternoon hours is determined mainly by the intensity of processes in the cold front zone and in the homogeneous polar continental and maritime air masses. Significant differences in precipitation distribution in cold and warm fronts are connected with the time of precipitation concentration within the diurnal period. The type of atmospheric front determines the layout of precipitation clouds, intensity of precipitation formation and the velocity of front movement. Copyright © 2006 Royal Meteorological Society

A 117 year series of hourly precipitation data from Krakow, South Poland and the Niedźwiedź classification of synoptic weather types were the basis of a detailed study of diurnal precipitation variation and atmospheric circulation types. The analysis of the relationship between precipitation and circulation types was restricted to the warm half of the year (May–October). During this period precipitation ispredominantly liquid. This paper discusses the role of theCarpathian orographic barrier in the development of the 24 hour precipitation pattern.

The impact of the synoptic situations on the occurrence of precipitation in Krakow is analysed. Daily records of precipitation from the period 1873–1999 were used, as well as the calendar of synoptic situations by T. Niedźwiedź. The study presents annual and long-term variations of daily precipitation, frequency of the synoptic situations, and frequency of precipitation for particular situations. For the 21 types of synoptic situations, the following characteristics were defined: average daily precipitation and its effectiveness ratio, maximum precipitation and the probability of occurrence of days with or without precipitation. Most precipitation occurs during the advection of air masses from the west and during the cyclonic trough, which is related to high frequency of occurrence of such situations. From among 21 synoptic situations, the following ones are the most favourable for the development of abundant precipitation: northeastern cyclonic situation (NEc), north cyclonic situation (Nc), cyclonic trough (Bc) and centre of low pressure (Cc). Copyright © 2001 Royal Meteorological Society

This chapter reports a study of extremely hot months (EHMs) during the period 1951–2010. Input data includes average, maximum and minimum monthly air temperatures, the number of days with tmax >25, 30, 35 °C and the number of days with tmin >20 °C, as recorded during three summer months (June–August) at 59 weather stations in Central and Eastern Europe. This body of data was used to identify and characterise EHMs, which were defined as months with an average monthly temperature exceeding the long-term average by two or more standard deviations (t ≥ tav. + 2σ). The frequency and geographical coverage of EHMs were also identified.

The paper discusses long-term change in snowfall, rainfall and mixed precipitation viewed in conjunction with air temperature and North Atlantic Oscillation (NAO) in winter (December–February). In the study of contemporary climate change and its effect on the hydrological cycle it is useful to focus on winter precipitation forms. A 146-year secular observation series from Krakow, spanning the period 1863–2008, was used to extract data on the number of days with precipitation and on precipitation amount broken down by form. Statistically significant trends were found in total and mixed precipitation, but not in snowfall and rainfall. The climate warming effect has contributed to a material decrease in the snowfall to total winter precipitation ratio during the second half of the 20th c. The highest impact of air temperature was found in the wintertime variation in number of days with snowfall while the NAO had a significant influence on the frequency and amount of both rainfall and snowfall.

The extreme weather phenomenon of heat waves poses a serious threat to humans and has been shown to contribute to increased sickness rates and even deaths, mostly in large cities. The paper concerns the occurrence of heat waves in Central Europe. Data was collected from five regional weather stations in Budapest, Krakow, Lvov, Prague and Vienna and included records of the average, maximum and minimum daily air temperatures during the period 1991–2006. The authors defined a heat wave as an unbroken period of at least three days with a maximum temperature of more than 30oC. The study demonstrates that the greatest intensity of heat stress is observed during short heat waves that lasted typically for three to four days and whose timing did not coincide at the different stations involved. Indeed, even longer heat waves, characterised by lower temperature values, were not always recorded at all the stations. This was due to the division of the region by mountain ranges, which impeded the flow of hot tropical air into southern Poland and western Ukraine.

The paper discusses nineteenth century visual and instrumental records of precipitation collected in those Polish territories falling in the Austro-Hungarian province of Galicia during the Hapsburg partition (1795–1918). Most attention is devoted to the observations and output of the weather station in the Astronomical Observatory of the Jagiellonian University in Cracow, which was the central station of several networks of weather stations and precipitation posts established during the second half of the nineteenth century. The station’s history dates back to 1 May 1792, when observations started at the initiative of the eminent scientist Jan Śniadecki. Initially, observations of precipitation were only visual. Daily observation logs were used to record the occurrence, type and intensity (drizzle, rain, rainstorm, thunderstorm, etc.) of precipitation events. Instrumental measurements of rain only started in August 1849, that is long after the first instrumental measurements of precipitation in southern Poland began in Lvov in 1811. In 1886, Professor F. Karlinski, head of the Astronomical Observatory, initiated pluviographic measurements in Cracow and these were first published in 1893. In the light of observations made in Cracow, high precipitation frequencies were noted in the 1830s and 1840s. Lower frequencies of precipitation, across all seasons, were recorded in the 1810s and 1820s. The second half of the nineteenth century was marked by a clearly lower degree of variation of precipitation days from year to year.

The paper presents variability of bioclimatic conditions in Cracow (Poland) during the period of 1826–2006. The data was gathered at the meteorological station situated in Botanical Garden in Cracow. Several bioclimate indices were applied to assess changes in winter (January), spring (April), summer (July) and autumn (October) seasons.

This paper discusses patterns of annual and monthly precipitation variability at seven weather stations in east central Europe (1851–2007). Precipitation patterns were compared to three simple regional indices of atmospheric circulation, i.e., western circulation, southern circulation and the cyclonicity (C) index and a relationship between precipitation and the North Atlantic Oscillation index was identified. Correlations of the monthly records and multiple regression, using a principal components’ analysis, helped determine the statistical significance of the dependence of precipitation on the circulation indices. The Mann–Kendall test revealed no trend to change in any of the precipitation series, but a certain spatial regularity could be discerned in the phase of the annual periodic component. A common feature of the variability in central European annual precipitation is the dry period identified in the 1980s and the first half of the 1990s. In the northern part of the region, above-average precipitation was noted from the 1960s through to the mid-1970s as a result of the frequent prevalence of depressions. South of the divide, the wettest period was recorded at the turn of 1930s/1940s. After a number of very wet years in the last decade of the twentieth century and the beginning of the twenty-first century, precipitation began to fall at all of the region’s weather stations. The C index is the strongest circulation-linked factor influencing precipitation in central Europe and it accounts for more than 40% of the variance in spatially averaged wintertime precipitation.

This paper investigates the relationship between maximum precipitation in Kraków and types of atmospheric circulation in southern Poland, as classified by Niedźwiedź. Three characteristics were used to define this relationship: maximum precipitation (Pmax), its duration (d) and probability of exceedance (p). The input data came from Kraków's uniquely long and homogenous pluviographic record spanning the period 1886–2007. Hourly precipitation values for the maximum precipitation events were identified and arranged in 1–24 hour intervals. They were then processed using the generalized extreme value (GEV) distribution to produce quantiles of maximum precipitation totals in each of the intervals and broken down by the corresponding circulation type. Differences between the development mechanisms are manifested in relationships between precipitation characteristics and their measure of randomness, i.e. exceedance probability. This paper demonstrates that maximum precipitation events depend on their duration d and atmospheric circulation. The maximum short-duration (one-hour) events occur primarily in either of two circulation types: (i) cyclonic with advection from the east and from the southeast or (ii) low-pressure centre and cyclonic trough. Maximum long-duration precipitation events (24 hour), on the other hand, occur in the cyclonic type of circulation with advection from the north and from the northeast.

A study was made of the relationships between the diurnal pattern of thunderstorm precipitation in Krakow and the types of air masses and atmospheric fronts prevailing over southern Poland during the period 1951–2006. The results of these investigations contribute to a better understanding of the physical processes taking place in the atmosphere that are associated with convective rainfall and may be used to improve the forecasting of the temporal distribution of convective precipitation. The elementary parameters of the daily precipitation cycle were identified, such as the amplitude and phase of the frequency and total thunderstorm precipitation. A separate analysis was performed of air mass and frontal precipitation. The 24-h thunderstorm precipitation cycle depends on the synoptic situation that determines the thermal and humidity properties of air masses. There is an afternoon peak in Krakow's general diurnal pattern of thunderstorm precipitation that is primarily linked to cold fronts and to air mass precipitation occurring in polar maritime air. Thunderstorm precipitation linked to warm fronts is less frequent and is concentrated in the evening. Copyright © 2009 Royal Meteorological Society

The paper reports on a study of extremely cool summers (ECS), a rare but significant phenomenon responsible for various adverse economic effects. These include, in particular, effects on agriculture and the tourist industry. The seasons, their spatial extent and individual characteristics were identified in Central and Eastern Europe. The research was based on average seasonal air temperatures (June to August) and the numbers of days with maximum temperatures >25, 30 and 35 °C and minimum temperatures >20 °C, as recorded at 59 weather stations during the period 1951–2010. An ECS was defined as having an average temperature at least 2 standard deviations (t ≤ tav. − 2σ) lower than the average at a given station during the study period. ECS occurred at only 34 of the 59 stations (58 % of all stations), one or two per station, mainly in the northern part of the study area. Six such seasons were recorded by at least 5 % of all stations in 1962, 1969, 1976, 1978, 1984 and 1994. The average temperature of an ECS was typically 2–3 °C lower than the long-term average. While some ECSs included an extremely cool month, most such seasons (58 %) were defined by low temperatures persisting for long periods in all summer months.

The paper focuses on exceptionally hot summers (EHS) as a manifestation of contemporary climate warming. The study identifies EHS occurrences in Central and Eastern Europe and describes the characteristic features of the region’s thermal conditions. Average air temperatures in June, July and August were considered, as well as the number of days with maximum temperatures exceeding 25, 30 and 35 ^{\circ}C, and with a minimum temperature greater than >20 ^{\circ}C, as recorded at 59 weather stations in 1951-2010. Extremely hot summers are defined as having an average temperature equal to or greater than the long-term average plus 2 SD. A calendar of EHSs was compiled and their spatial extent identified. The region experienced 12 EHSs, which occurred in a given year at 5 % or more stations (1972, 1981, 1988, 1992, 1997, 1998, 1999, 2002, 2003, 2006, 2007 and 2010). The EHS frequency of occurrence was found to be clearly on an increase. Indeed, only one EHS occurred during the first 30 years, but these occurred five times during the last 10 years of the study period. Their geographical extent varied both in terms of location and size. EHSs were observed at 57 out of the total of 59 weather stations in the study (the exceptions were Pecora and Cluj). The average air temperature of EHSs tended to exceed the relevant long-term average by 2-4 ^{\circ}C. The summer of 2010 was among the hottest (temperature anomaly 5.5-6 ^{\circ}C) and spatially largest.

Investigation of extreme thermal conditions is important from the perspective of global warming. Therefore, this study has been undertaken in order to determine the frequency, timing and spatial extent of extremely cold months in winter time at 60 weather stations across Europe over a sixty-year period from 1951 to 2010. Extremely cold months (ECMs) are defined as months in which the average air temperature is lower than the corresponding multi-annual average by at least 2 standard deviations. Half of all the ECMs occurred in the years 1951–1970 (33 out of 67). The lowest number of ECMs was recorded in the decade 1991–2000, but since the beginning of the 21st century, their density and territorial extent has started to increase again. The extremely cold months with ECMs of the greatest spatial extent, covering at least one third of the stations (over 20 stations), included: February 1954 (22), February 1956 (36), January 1963 (25), and January 1987 (23 stations).