The comparation of weather types in the years of extreme drought over Croatia Dunja Plačko-Vršnak, Krunoslav Mikec, Marija Mokorić Meteorological and Hydrological Service of Croatia Introduction Winter seasonSpring season The analyzed synoptic situation (DWD surface analysis, in some cases with help of 850 hPa geopotential field) were classified in the weather types (according to Poje (1965)) for several regions in Croatia (northwest region – Central Croatia, North, Central and South Adriatic). The method is subjective. The weather types with similar weather characteristic are grouped in 6 weather regimes (Table 1). The extreme years were compared mutually and then to mean relative frequency of weather types and regimes for reference period The characteristic synoptic charts related to significant differences in weather types (regimes) are shown and commented. Data and Methods Conclusions Since the year 2000 there were 3 extremely drought years in Croatia: 2003, 2011 and The long term with lack of precipitation was observed in whole country having a great impact on reducing in agricultural production and causing problems in water supply. In the summer 2012 authorities declared a state of natural disaster for inland and North Adriatic region. The consequences of extreme drought was evident also in increased number of wild fires, not only in Adriatic region, but also in the year 2003 in mountainous region and in the 2012 in continental parts of northwest and east Croatia. For example in the summer season of 2012 in the North Adriatic there were 100 wild fires with more than 1000 ha of burned area. The comparation of weather types and weather regimes in the years of extreme drought over Croatia was done. The significant difference in weather types and regimes for every season is presented here. during the analyzed period in all regions annual relative frequency of radiative regime was above and relative frequency of precipitation regime below the average in 2003 radiative regime was most frequent while in 2011 relative frequency of SE advection regime and wind regime (which also contributes to dry weather) was significantly higher than average, as well as radiative regime in 2012 anomalies related to usual weather types and regimes were not so explicit and drought conditions were not only a result of these anomalies but also a conseqence of long drought period in 2011 this analisys pointed out that Central European anticyclone positioned more to the north and cyclonic activity over Mediterranean more to the south than usual caused drought conditions in Croatia Precipitation regimeC1Eastern sector of cyclone C2Southern sector of cyclone T1Front side of the trough T2Axis of the trough WSWest transition state SWSSouthwest transition state SSSouth transition state Radiative regimeA1Eastern sector of anticyclone A2Southern sector of anticyclone A4Northern sector of anticyclone hrRidge of high pressure hvBridge of high pressure NGaNon-gradient pressure field anticyclonic NGcNon-gradient pressure field cyclonic SE advection regimeA3Western sector of anticyclone SESSoutheast transition state NW advection regimeNWSNorthwest transition state T3Rear side of the trough Wind regimeC4Northern sector of cyclone NSNorth transition state NESNortheast transition state ESEast transition state Other C3Western sector of cyclone CcCenter of cyclone ZT1Front side of the zonal trough ZT2Axis of the zonal trough ZT3Rear side of the zonal trough AcCenter of anticyclone TtPressure trough Climate annual reports for 2003, 2011 and 2012 for precipitation – 2003 and 2011 were mostly very dry and extremely dry, while in 2012 only summer season was extremely dry Table 1: weather regimes, weather types and weather types abbreviations Croatian regions as well as radiative regime, relative frequency of wind regime was also above average in winter 2003 relative frequency of C4 weather type (wind regime) was significantly higher than average in all regions cyclone tracks were moved more to the south than usual during winter 2003 DWD surface analysis for 19 January 2003, 00 UTC in spring 2011 relative frequency of wind regime was 2 times higher than average also, relative frequency of Tt weather type (regime other) in 2003 in Central and South Adriatic was more than 2 times higher than average cyclone tracks were moved even more to the south than in winter 2003 so the weather type was characterized only by “isobare curvature” (cyclonic), not by cyclone itself DWD surface analysis for 17 April 2003, 00 UTC frequency of radiative regime in summer in analyzed years in all regions was 70 to 90 % relative frequency of Hr weather type (radiative regime) in 2011 and 2012 was almost 3 times higher than average characteristic synoptic situation was consequence of high pressure field stretching from the west or southwest DWD surface analysis for 24 June 2012, 00 UTC Summer seasonAutumn season DWD surface analysis for 17 November 2011, 00 UTC relative frequency of SE advection regime in autumn 2011 was significantly higher than average, especially in Adriatic region in 2011 in all regions relative frequency of A2 weather type was significantly higher than average anticyclone tracks were moved more to the north and to the east than usual