INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 31: 2183–2193 (2011) Published online 7 October 2010 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/joc.2230 Weather types accompanying very high pressure in Krakow in the period 1901–2000 Zuzanna Bielec-Bakowska a * and Katarzyna Piotrowicz b a Department of Climatology, Faculty of Earth Science, University of Silesia, Bedzinska 60, Sosnowiec 41-200, Poland b Department of Climatology, Institute of Geography and Spatial Management, Jagiellonian University, Gronostajowa 7, Krakow 30-387, Poland ABSTRACT: The paper presents a classification of weather types observed in Krakow during the 20th century on days with particularly strong highs. The classification was based on daily values of a number of weather elements recorded at Krakow’s Historic Weather Station during the period 1901–2000. Days with very high pressure were defined as those with an air pressure at 12 UTC equal to or greater than the 99th percentile of all the cases analysed (≥1037.5 hPa). A slightly modified version of a classification developed by Wo´ s (1999) was used to determine weather types on each of the days identified. Very high pressure was found to have occurred solely during the cold half of the year (October–March). It was mostly accompanied by fairly frosty (9---) or moderately frosty (8---) weather types; subtype: sunny or with little cloud amount and very sunny (-02-) and very cloudy, without sunshine or with little sunshine (-20-); and weather class: without fog (---0). No significant annual or seasonal trends were found in the occurrence of days with very high pressure or in the various weather types. Copyright  2010 Royal Meteorological Society KEY WORDS strong baric systems; weather types; classification; Krakow; Poland Received 2 February 2010; Revised 14 August 2010; Accepted 25 August 2010 1. Introduction Climatologists have recently given a strong focus to the climate changes observed during recent decades and to their effects. One of the aspects of these changes is the occurrence of specific weather types that are typically linked to the atmospheric circulation changes and to the occurrence of characteristic types of synoptic situation, the time of their occurrence (annual course) and persis- tence. An insight into the nature of change in weather types and their frequency of occurrence, especially of exceptional cases, in a given area is important both to improve the understanding and for applied purposes. Changing weather patterns force changes in a number of human activities, such as water management, agricul- ture, construction or transport; they strongly affect human health and well-being and require adaptation. The term ‘weather type’ is used in various fields of climatology, including in complex climatology (a spe- cialised area of climatology that evolved in the 1920s and the fundamentals of which were developed by Fiedorov and Czubukov; Kozlowska-Szcz¸ esna, 1965), bioclima- tology and in synoptic meteorology and climatology (Olszewski, 1967; Nied´ zwied´ z, 2003). In complex cli- matology, a weather type is defined as a 24-h course * Correspondence to: Zuzanna Bielec-Bakowska, Department of Cli- matology, Faculty of Earth Science, University of Silesia, Bedzinska 60 Street, Sosnowiec 41-200, Poland. E-mail: zuzanna.bielec-bakowska@us.edu.pl of meteorological elements or their complexes follow- ing a pattern. The earliest classifications of weather types so defined were proposed by Fiedorov (Kozlowska- Szcz¸ esna, 1965), Howe (1925), Nichols (1925, 1927) and Switzer (1925). In Polish literature, this type of clas- sification was proposed by Wo´ s (1977, 1999) and was successfully used by Kaszewski (1992), Marsz (1992), Lotko-Lozi´ nska (1994), Ko ˙ zuchowski (1996) and Fer- dynus (2004). Bioclimatologists use weather types to assess bioclimate, as the frequency of weather situa- tions has an influence on the human body and can be important for climatotherapy (e.g. classification by Fiedorow and Czubukow; Kozlowska-Szcz¸ esna, 1965; Bla ˙ zejczyk, 1979, 2004). To a synoptic climatology, how- ever, weather type is defined as a particular type of atmo- spheric circulation (Stefanicki et al., 1998; Littmann, 2000; Bissolli and Dittmann, 2001; Buchanan et al., 2002; Sheridan, 2002, 2003; Brown, 2004, 2005; Bo´ e and Terray, 2008; Moron et al., 2008; Makra et al., 2009). Most published research on the weather of a given area investigates one or a few meteorological parameters in terms of frequency of occurrence in certain synoptic situations (Trigo and DaCamara, 2000; Svensson et al., 2002; Brown, 2005; Twardosz, 2007). Other approaches involve an analysis of synoptic situations and finding values of selected meteorological parameters or indices on days when these situations occur (Nied´ zwied´ z, 1981; Post et al., 2002). There is little research, however, that looks at the relationship between circulation types Copyright  2010 Royal Meteorological Society