In the northern Bay of Bothnia, the freezing started towards the end of October, or two weeks earlier than average; in the eastern Gulf of Finland, the ice cover started forming in early November three weeks earlier than average and in the Sea of Bothnia, the Archipelago Sea and the western part of the Gulf of Finland, towards the end of November more than three weeks earlier than average.

The early part of December was cold and ice freezing was fast. The Quark received its ice cover on the 7th of December, approximately three weeks earlier, and the Bay of Bothnia in mid-December a month earlier than usual. After mid-December, a windy, milder weather system set in, during which the ice on the open seas of the Bay of Bothnia was packed in the northern part of the Bay, and that in the Gulf of Finland to the mouth of the Bay of Vyborg and to the east of Seskar island. Towards the end of December, there was another cold spell, and ice was formed in all sea areas. At the turn of the year, the Bay of Bothnia, the Gulf of Finland and the Archipelago Sea were totally covered by ice, and in the Sea of Bothnia, a 10 to 25 nautical miles wide band of ice was found off the shore. In the Gulf of Finland, the ice edge extended to the longitude of Jussarö.

The beginning of January was cold, and ice was formed even in the northern Baltic Sea. On the 7th of January, almost the whole Sea of Bothnia was covered with ice, and the ice edge extended from the Sea of Åland to the west of Bogskär and the western side of Ventspils. The ice sheet over the Bay of Bothnia and the Gulf of Finland grew thicker. In mid-January, a mild and windy weather type set in. In the Sea of Bothnia, the thin ice sheet was pressed against the Finnish coast forming a thick zone of ridged ice off the coast. The ice field in the northern Baltic Sea drifted towards the fast ice edge in the Archipelago Sea and the western Gulf of Finland forming a brash barrier. New, thick areas of ridged ice were formed in the ice fields of the Gulf of Finland.

February began with a cold spell, and ice was formed over all sea areas, so that the Gulf of Bothnia, Sea of Åland and the Gulf of Finland were totally covered by ice, and in the Northern Baltic Sea, the ice edge was found in the line Söderarm-Bogskär-Ventspils. In February, the weather was variable with intermittent mild and cold spells, causing the ice cover to decrease and increase in turns. At the end of February and the beginning of March, a longer cold spell took over, during which the maximum ice extent, 233 000 km², was reached on the 5th of March. The Gulf of Bothnia and the Gulf of Finland were covered by ice, and the ice edge extended to the northern Baltic Sea from Öland via Häradskär to the north of Gotska Sandö and from there, west of Ventspils to Liepaja. In the archipelago of the southern Baltic Sea there were ice in places. Soon after this, the weather became mild, and south-westerly winds drove the ice against the Finnish coast in the Gulf of Bothnia, resulting in the formation of ridged ice that presented navigation problems in front of the fast ice. A lead was formed in the western Gulf of Finland to the west of Porkkala, whereas to the east of Porkkala, thick ridged ice difficult to force was formed. For the rest of the month of March, the weather remained mild, and the ice started receding and breaking up in the northern Baltic Sea.

In early April, the ice in the Sea of Bothnia drifted to the open sea and in the Gulf of Finland, the ice kept drifting from coast to coast, leaving a lead in the opposite side. In April, however, the weather was cool and the ice was slow to melt.

The ice in the Archipelago Sea broke up in the very beginning of May, almost two weeks later than average. In the western Gulf of Finland and Sea of Bothnia, the ice broke up towards the beginning of May, and in the eastern Gulf of Finland before mid-May, more than two weeks later than average. Towards the end of May, the ice broke up first in the southern Bay of Bothnia approximately a week later than normal, and finally in the northern Bay of Bothnia on the 28th of May, or around the usual time.

The maximum thickness of fast ice in the northern Bay of Bothnia was 70 to 90 cm, in the Sea of Bothnia 60 to 75 cm, in the western Gulf of Finland 50 to 65 cm and in the eastern Gulf of Finland, 65 to 80 cm. The maximum ice thickness in open sea was 40 to 60 cm in the Bay of Bothnia, 20 to 40 cm in the Sea of Bothnia, 5 to 20 cm in the northern Baltic Sea and 40 to 75 cm in the Gulf of Finland.

The duration of the ice winter was longer than average in all sea areas, being some two weeks longer in the northern Bay of Bothnia, some three weeks longer in the southern Bay of Bothnia and over one month longer in the Sea of Bothnia, Archipelago Sea and the Gulf of Finland.

Simo Kalliosaari