24 
Table 2.9. Ice conditions in the strong to extremely strong ice winters in the period 1961-1990 
Number: 8 (27 %) 
Ice-free: 0 winters 
Area 
Earliest first ice 
Earliest last ice 
Minimum number of 
days with ice 
Minimum duration of 
ice season 
Minimum of the 
ice thickness 
Sea area 
09.12. 
23.02. 
30 
39 
15 cm 
Szczecin Lagoon 
16.11. 
10.03. 
61 
73 
20 cm 
Area 
Average first 
ice 
(median) 
Average last 
ice 
(median) 
Average number of 
days with ice 
(median) 
Average duration of 
ice season 
(median) 
Average max. ice 
thickness 
Sea area 
31.12. 
26.03. 
49 
78 
32 cm 
Szczecin Lagoon 
21.12. 
31.03. 
98 
111 
40 cm 
Area 
Latest first ice 
Latest last ice 
Maximum number of 
days with ice 
Maximum duration of 
ice season 
Maximum of the 
ice thickness 
Sea area 
18.01. 
09.04. 
105 
117 
60 cm 
Szczecin Lagoon 
10.01. 
19.04. 
134 
134 
100 cm 
Ice formation in strong to extremely strong ice winters usually starts in the third decade of 
December in both areas. The dates of freezing are very variable from season to season, also in 
the same ice winter class. Ice may form in mid-November in Szczecin Lagoon, and at the 
beginning of December in Pomeranian Bay. In some strong winters, ice was first observed in 
January. The ice disappears, in the areas investigated, on average by late March. The ice in 
strong ice winters rarely melts as early as the end of February. In extremely strong ice winters, 
the ice may remain in the Pomeranian Bay until early April, and in Szczecin Lagoon until mid- 
April. The thickness of level ice reaches values of 30 to 60 cm in sea areas, and 40 to 100 cm 
in Szczecin Lagoon. The ice season lasts from 100 to 134 days in Szczecin Lagoon, and up to 
about 100 days in the Pomeranian Bay. 
2.4. Comparison of the air temperatures and of the ice conditions in the different ice 
winter severity types 
The formation of sea ice depends on the prevailing weather conditions, primarily on the air 
temperatures. The air temperature variations in mild, moderate and strong ice winters under 
consideration are shown in Figure 2.5. 
5-day average of air tem perature 
1 9 8 8/8 9 1 9 7 6/7 7 1 9 8 6/8 7 
Figure 2.5. Variation of air temperature in Trzebiez (Szczecin Lagoon)