Global warming vs local reality: Poland's exceptionally cool May 2025

Poland’s location in the mid-latitudes determines a moderate influx of solar radiation and characteristic circulation conditions that strongly control weather variability. Of particular importance is the dominance of westerly circulation, enhanced by the zonal configuration of relief. The frequent passage of cyclones and atmospheric fronts, together with the advection of air masses with highly contrasting thermal properties, results in pronounced weather variability. Depending on the direction of air-mass advection, both extremely warm and extremely cold conditions may occur.

Since the late 20th century, the climate has been characterized by the predominance of anomalously warm months, seasons, and years. Notable examples include the exceptionally hot summer of 2003 in Western Europe and the summer of 2010 in Eastern Europe, both of which caused thousands of excess deaths among populations unaccustomed to prolonged heat stress. At the same time, extreme cold events still occur. Although they have become less frequent and less intense than during the 20th century, they continue to generate severe economic and biometeorological impacts. An example is January 2017 in the Balkan Peninsula, which was among the coldest and snowiest months on record in that region.

In the current year, a pronounced negative temperature anomaly was also observed: in May, snowfall and widespread frost occurred over large parts of Poland, as widely reported by the media. The aim of this study was therefore to assess how strongly thermal conditions in May 2025 deviated from the long-term climatological mean in Poland. Specifically, the study seeks to quantify the magnitude of the air-temperature anomaly and to identify the synoptic conditions responsible for the persistence of anomalously low temperatures.

The primary dataset consists of mean monthly air temperatures for May for the period 1951–2025 from 60 synoptic stations in Poland. These publicly available data were obtained from the database of the Polish national meteorological service (IMGW-PIB, https://danepubliczne.imgw.pl/). This dataset was used to calculate the magnitude of the temperature anomaly in May 2025. Anomalies were expressed both in absolute terms (°C) and in standardized units (multiples of the standard deviation, SD). A second dataset, also obtained from IMGW-PIB, comprises daily mean, maximum, and minimum air temperatures for May for the 75-year period 1951–2025 from selected stations. Synoptic conditions were analysed using surface and upper-air weather charts from the Polish (meteo.imgw.pl) and German (www.wetter3.de) meteorological services.

Preliminary results indicate that the cold conditions over Poland were primarily controlled by low-pressure systems that induced advection of cold air from the northern sector. Their persistence was favoured by a characteristic omega-blocking pattern over Western Europe and the presence of a deep upper-level trough over Central Europe. This configuration effectively inhibited the eastward progression of baric systems, allowing the prevailing weather regime to persist over the region for an extended period.