2013),

this research revealed some significant differences during its persistence. An especially strong shift from general circulation patterns is observed during the developing phase of a dry period. The domination of meridional vs. zonal circulation patterns remains during the persisting phase, Cyclopamine cell line while ‘extra’ zonal circulation patterns occur during the attenuation phase of a dry period. Prolonged dry anomaly alterations to humid periods are very common in May–September in Lithuania. Moreover, the findings are confirmed by analyses of the atmospheric circulation and extreme conditions in the region (Rimkus et al., 2011 and Rimkus et al., 2013). The analysis of 14 cases when HTC was less than or equal to 0.5 for 15 consecutive days revealed the fact that the frequency of weather types in the whole ABT-888 order of Lithuania is significantly different from the respective values in the various regions (Table 2). Even though Lithuania is not a large country (ca 65 300 km2) this can be explained by different climatic features (Figure 1). The whole country lies in the air mass transformation zone between oceanic and continental climates: it is a hemiboreal climate (type Dfb) according to the Köppen-Geiger climate classification (Peel et al. 2007). Particularly significant differences between the western and southern parts of the country have already been observed in dryness analyses for the Baltic Sea region (Pankauskas and Bukantis, 2006 and Rimkus et al., 2012) and

the Nemunas river basin (Rimkus et al. 2013). Another possible not reason is methodological. We use the subjective (Werner & Gerstengarbe 2010) vs. objective (Fleig et al. 2011) Hess and Brezowski atmospheric macro-circulation form classification. Although the classification has been modified for Lithuania, there are shifting possibilities of weather patterns because of geographical features and long dry period phases (> 2 weeks). Different weather conditions could be identified using both methods, especially at the beginning and end of dry phases. A previous study by Bukantis & Valiuškevičienė (2005) showed that extreme air temperatures are mostly determined by meridional,

and extreme precipitation – by zonal circulation forms. However, extreme weather events are generated by diverse circulation forms if the whole country was used for determining circulation forms. Drought formation cluster analysis (Figure 1) explains clearly that circulation forms should be analysed for different parts of the regions, even though the territory is not that big. This statement was already endorsed by Rimkus et al., 2011 and Rimkus et al., 2012. Another possible reason for the variance is the inequality of dryness trends (Rimkus et al. 2013) in different parts of Lithuania. The dryness frequency remains practically the same in the western part of the country, while in other parts dryness tends to decrease. Dry periods usually correspond to high pressure fields (Parry et al., 2010 and Fleig et al., 2011).