**Arkadiusz M. Tomczyk \*, Marek Półrolniczak and Leszek Kolendowicz**

Department of Climatology, Adam Mickiewicz University in Pozna ´n, B. Krygowskiego 10, 61–680 Pozna ´n, Poland; marekpol@amu.edu.pl (M.P.); leszko@amu.edu.pl (L.K.)

**\*** Correspondence: atomczyk@amu.edu.pl

Received: 27 April 2018; Accepted: 25 May 2018; Published: 28 May 2018

**Abstract:** The objective of the paper was to characterize the occurrence of cold days and cold waves in Pozna ´n in the years 1966/67–2015/16, as well as to characterize thermal conditions in the city during selected cold waves in the years 2008/09–2015/16. The study was based on daily data on maximum and minimum air temperature for station Pozna ´n-Ławica from the years 1966/67–2015/16 and daily air temperature values from eight measurement points located in the territory of the city in different types of land use from the years 2008/08–2015/16. In addition, to characterize thermal conditions during selected days forming cold waves, satellite images were used, on the basis of which the land surface temperature (LST) was calculated. A cold day was defined as a day with daily maximum temperature (Tmax) below the value of 5th annual percentile of Tmax, and a cold wave was defined as at least five consecutive cold days. The study showed an increase in Tmax in winter, which translated to a decrease in the number of cold days over the last 50 years, although the changes were not statistically significant. Thermal conditions in the city showed high variability in the winter season and during the analyzed cold waves.

**Keywords:** air temperature; cold days; cold waves; climate change; urban area types; Pozna ´n; Poland
