In the northern Bay of Bothnia the freezing started in the beginning of December, approximately a month later than average, in the eastern parts of the Gulf of Finland, in the Bay of Vyborg and off St. Petersburg at the same time, approximately a week earlier than average. In the southern Bay of Bothnia and the Quark the freezing started in mid-December, approximately a week later than average, in the Sea of Bothnia, the Archipelago Sea and the western Gulf of Finland after mid-December, at the average time. In the end of December there was a period of cold weather and ice was forming in the Bay of Bothnia, off the archipelago, and in the other sea areas to the outer archipelago.

In the beginning of January the weather was mild and only in the Bay of Bothnia new ice was occasionally forming, but the new ice was broken by the wind and formed a brash ice barrier at the compact ice edge. In the end of January the weather became colder and ice was forming in all sea areas. The Quark was covered with new ice, in the Sea of Bothnia new ice was forming off the archipelago, the Archipelago Sea was covered with ice and in the eastern Gulf of Finland the ice field spread to Gogland. At the same time the fast ice in the archipelago got thicker. In the end of January the weather, however, became milder and the ice situation decreased. In the northern part of the Bay of Bothnia the ice was ridging against the fast ice, in the Sea of Bothnia a brash ice barrier was formed at the fast ice edge and in the eastern Gulf of Finland the ice drifted to east of Motshnyj.

In the beginning of February the weather became colder and the freezing began again in all sea areas. In mid-February the Bay of Bothnia was completely covered with ice that is approximately a month later than average. At the same time in the Sea of Bothnia there was 20-30 nautical miles of ice off the archipelago, in the Gulf of Finland the ice edge ran along the line Hanko – Pakri and in the northern Baltic Sea there was ice to outside the archipelago. In the end of February the weather was milder and the ice situation decreased a little. The ice drifted northeastwards and new ridges formed in the Bay of Bothnia and the Gulf of Finland.

In the beginning of March the cold increased and more ice was rapidly forming. The largest ice cover – 211 000 km² – was reached on March 16. The Gulf of Bothnia and the Gulf of Finland were completely covered with ice. In the northern Baltic Sea the ice edge ran from the northern tip of Öland via Häradskär and Almagrundet to northwest of Ristna and from there via west of Saaremaa and Ventspils to the south of Klaipeda. There was also thin ice in the archipelago in the southern Baltic Sea. After this the ice situation began to decrease gradually.

In the beginning of April most of the open Sea of Bothnia was open and in the northern Baltic Sea the ice edge ran along the line Utö–Pakri. In April the weather was cool and the ice melted slowly. In the Gulf of Finland, the Archipelago Sea and the Sea of Bothnia the ice disappeared in the beginning of May, more than a week later than average. The Quark became free of ice in the beginning of May and the Bay of Bothnia in the very end of May as usual.

The maximum thickness of the fast ice in the northern Bay of Bothnia and in the Sea of Bothnia was 50–70 cm, in the Archipelago Sea 30–40 cm and in the Gulf of Finland 40–65 cm. The thickness of the open sea ice was 30–60 cm in the Bay of Bothnia, 10–30 cm in the Sea of Bothnia, 5–25 cm in the northern Baltic Sea, 20–40 cm in the western Gulf of Finland and 35–55 cm in the eastern Gulf of Finland.

In the Bay of Bothnia the duration of the ice winter was approximately three weeks shorter than average, in the Quark, the Sea of Bothnia and the northern Baltic Sea it was average and in the Archipelago Sea and the Gulf of Finland approximately a week longer than average.

Simo Kalliosaari