The report presents the results of studies concerning variability of the thermal and precipitation conditions in Poland in the second half of 20th century. The focus of the report was on unfavourable period from the point of view of agriculture production. The study was based on spatially averaged values of air temperature and precipitation sums from the consecutive years 1951-2000. Significant increase of temperature was observed for the spring, which had an noticeable effect on the change in the duration of vegetative period (on average in the last two decades of the 20th century the dates of the beginning of vegetative period �moved� into the last pentad of March). Winters got milder. Quite characteristic was certain coolness in June and in autumn (earlier end of vegetative period). The amount of precipitation does not show any significant trend. In the last two decades of the 20th century the growth in the warming rate was observed. The growth showed up not only in the winter-spring period (I-V) but also in the warm part of year. High temperature in summer together with shortages of precipitation (especially in the years 1981-1994) gave rice for dry spells and droughts. The end of the 1990s witnessed balance in the amount of precipitation. Seasonal structure analysis for anomalous years with respect to temperature and amount of precipitation helped to determine the years especially unfavourable for agriculture production. It was shown that dry spell (determined on the basis of hydrothermical coefficient of Sielianinow) in vegetative period together with the shortening of vegetative period account for dozen and so percent of variability of corn crops.