Very warm and tropical nights in voivodeship cities in Poland in the period 1971–2020
Very warm and tropical nights in voivodeship cities in Poland in the period 1971–2020

Summary/Abstract: Using minimum air temperature data for the period April–September 1971–2020 obtained from 16 meteorological(synoptic) stations of IMGW-PIB located within the administrative boundaries of voivodeship cities in Poland, the temporaland spatial distribution of very warm (from >18°C to ≤20°C) and tropical (>20°C) nights was determined. The paper presentsthe results for thirty-year-long reference periods (1971–2000, 1981–2010, 1991–2020). A positive trend of mean minimum airtemperature in all stations in each month of the period April–September was demonstrated, and was particularly pronouncedin 1991–2020. Since 2010, there has been a considerable increase in the number of very warm and tropical nights, most evidentin Gdańsk and Gorzów Wielkopolski. It was found that very warm and tropical nights occur most frequently as isolated cases,rarely in a series of two or three nights, and particularly rarely in a series of six and more episodes. The longest seriesof thermally characteristic nights was found in Warszawa in 2018 between 25 July and 5 August. Based on the earliestand latest dates, it was found that, in the analysed years, very warm and tropical nights occur earlier but also disappear later.

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