Ice formation: The sea began to freeze in the northern Bay of Bothnia in late October. The freezing process was slow until late November, when ice formation started in the eastern part of the Gulf of Finland as well. In early December the ice cover in the Bay of Bothnia extended. Now ice formation started in the southern part of the Bay, in the Quark and in the Sea of Bothnia as well. Meanwhile the weather changed, becoming mild and windy. The ice in the Bay of Bothnia drifted northwards, forming ridges off Kemi. At the end of December there was a cold spell which caused the ice cover in the Bay of Bothnia and the Gulf of Finland to extend and strengthen. Now the freezing process started in the Archipelago Sea and the western Gulf of Finland as well.

In general, the time of ice formation was normal, except for the northern Bay of Bothnia and the eastern Gulf of Finland, where ice began to form about a week earlier than the average.

January: In early January the weather became mild and windy. Ridges were formed off the coast in the northern Bay of Bothnia and the eastern Gulf of Finland. The freezing process was slow until the end of the month when ice began to form in the Bay of Bothnia, the Quark, the Sea of Bothnia, the Archipelago Sea and the Gulf of Finland.

February: In early February ice formation continued. The Bay of Bothnia was covered in its entirety on 1 February, two weeks later than the average. In the Gulf of Finland the ice cover extended from the east to the longitude of Helsinki. After mid-February the weather was mild again and the ice began to decrease. In the Bay of Bothnia ridges formed against the fast ice off the Finnish coast. At the end of February, a wide lead had formed in the Bay of Bothnia, from Skellefteå to the Quark. In the Gulf of Finland there was ice on the high sea east of Hogland.

March: In early March there was a cold spell, during which the ice cover reached its largest extent. This happened on March 11th when the ice covered 130 000 km², i.e. the Bay of Bothnia, the Quark and the Archipelago Sea. In the Sea of Bothnia there was ice from the north to the latitude of Storkallegrund. Southward along the coast there was a belt of ice, 20–40 M long. The ice cover in the Gulf of Finland reached from the east to the longitude of Hanko. The Gulf of Riga was also covered by ice. Then the ice slowly started to decrease. The thin ice in the Sea of Bothnia broke up and formed dense floes off the Finnish coast.

Break-up of the ice: The Archipelago Sea became ice free about the average time, i.e. end of April. The Sea of Bothnia was equally ice free by the end of April and the Gulf of Finland in early May, a week later than the average. As usual, the last floes of ice in the Bay of Bothnia melted at the end of May.

Max. ice thickness, fast ice: Bay of Bothnia, northern part 70–90 cm, Bay of Bothnia, southern part 50–70 cm, Sea of Bothnia 40–50 cm, Archipelago Sea 25 cm, Gulf of Finland, western part 25–30 cm, Gulf of Finland, eastern part 55–60 cm.

Max. ice thickness, open sea: Bay of Bothnia, northern part 40–60 cm, Bay of Bothnia, southern part 20–40 cm, Sea of Bothnia 10–30 cm, Gulf of Finland, western part 5–30 cm, Gulf of Finland, eastern part 40–70 cm.

Length of ice season: The ice season was of medium length in the northern Bay of Bothnia but shorter than the average in the southern part and in the Quark. In the Sea of Bothnia and the Archipelago Sea the season was three weeks and in the western Gulf of Finland more than a week shorter than the average. In the eastern part of the Gulf, the ice season was, by contrast, more than two weeks longer than the average.

Simo Kalliosaari