*3.2. Cold Days and Cold Waves in the Years 1966–2015 (Pozna ´n-Ławica)*

Cold days (i.e., days with a maximum temperature below −1.6 ◦C) in Pozna ´n occurred for 18 days in a year on average. In particular seasons, their number was largely variable, as suggested by the value of standard deviation amounting to 12.6. The number of cold days changes from 1 day (1974/75) to 50 days (1969/70) (Figure 3). A decrease in the number of cold days was recorded in the analyzed period, although the changes were not statistically significant. The analyzed days occurred from November to March, although their highest number was recorded from December to February with a maximum in January (43.9% of all recorded days). The first cold day was observed the earliest on

4 November 1980, and the latest on 23 March 2013. According to the above data, the potential period of occurrence of cold days in Pozna ´n amounted to 140 days.

**Figure 3.** Number of cold days in the period 1966/67–2015/16 and the frequency of occurrence of cold days in months.

A total of 59 cold waves were observed in the analyzed multi-annual period. They lasted for a total of 551 days (Table 2). The lowest number of cold waves was recorded in the years 1996/97–2005/06 (8 cases), and the highest in the years 1976/77–1985/86 (16 cases). Waves of 5 and 7 days were the most frequent, respectively 14 and 12. The longest cold wave occurred in winter 1984/85 and lasted for 27 days from 26 December to 21 January. An equally long cold wave was recorded in the season 1996/97. It lasted for 24 days (from 20 December to 12 January). The average length of cold waves in the analyzed multi-annual period amounted to 9.3 day, and in particular decades it varied from 7.9 (1986/87–1995/96) to 10 days (1996/97–2005/06). Cold waves occurred from November to March and were the most frequent in January (52.5% of all waves). The earliest cold wave in the analyzed multi-annual period was observed in 1993, from 19 to 23 November, and the latest from 1 to 7 March 1987.


**Table 2.** Characteristics of cold waves in the period 1966/67–2015/16 in Pozna ´n-Ławica.

The average Tmax during the analyzed cold waves amounted to −5.5 ◦C, and Tmin −11.5 ◦C. The lowest average Tmax and Tmin was recorded during the cold wave in 1987 (7–22.01). They amounted to −10.6 ◦C and −18.3 ◦C, respectively. The highest average Tmax and Tmin were recorded during the wave in 1978. They equaled −2.9 ◦C and −5.5 ◦C, respectively. During the longest cold wave, i.e., a wave lasting from 26 December 1984 to 21 January 1985, the average Tmax amounted to −7.0 ◦C, and average Tmin −12.8 ◦C.
