Jan Zimnol
Geographical Studies, Issue 159, 2019, pp. 67 - 86
https://doi.org/10.4467/20833113PG.19.020.11488The study presents the spatial and temporal variability of warm and cold days occurring in the years 1966–2017 at five meteorological stations representing four peripheral areas and the centre of Poland. The analysis was based on the daily maximum air temperature values. A warm or cold day was considered as a day during which the maximum temperature was respectively higher or lower than the average daily temperature by a value of 1.28 standard deviation for a given calendar day. The obtained results indicate an increase in the frequency of the occurrence of warm days sequences and a decrease in the number of sequences of cold days, especially after 1990. The analysis also found a clear differentiation of the annual course of the considered days depending on the geographical location of the area in question. The most distinctive is the north-western region of Poland, where the highest number of warm days was recorded. In contrast, the area of southern Poland is characterized by a higher number of cold days. Most of the analyzed days occurred as one- or two-day long sequences, constituting approximately 70–80% of all cases. In the analyzed period, short (lasting 3–5 days) waves of warm or cold days were most frequent, and the longest waves (lasting at least 11 days) usually accounted for less than 1% of all cases recorded at a given station.