The ice formation in the innermost bays of the northern part of the Bay of Bothnia began with the middle of November. At the beginning of December there was 1–10 cm thick level ice in the inner archipelago of the Bay of Bothnia and new ice off St. Petersburg. In the beginning of December the weather was extraordinarily mild and no ice formation occurred. During Christmas weather was cold and the amount of ice increased. The first Finnish icebreaker began assistance on 25th of December. After this, the weather became milder again. In total, December and the first half of January were milder than normal.

Then a short cold spell began, lasting until 23rd of January, still resulting in the culmination of the ice winter – the extent of ice reached 51 000 km². 

After another cold period around the 5th of February the extent of ice reached 50 000 km². After this, the weather became milder, and the southerly winds pushed the ice fields together. The rest of February was unusually mild. In the beginning of March the ice extent was only 20 000 km².

March was also warmer than usual. In the end of March the ice-covered area was unusually low, only about 15 000 km². April was also warmer than average and at the end of the month, ice appeared only in the Bay of Bothnia. Finally the last ice melted, earlier than ever, on 7th of May. The Baltic Sea was ice-free two weeks earlier than usual.

The maximum thickness of the fast ice was 35–55 cm in the Bay of Bothnia, 20–35 cm in the Sea of Bothnia and 30–40 cm in the Gulf of Finland. The thickness of the pelagic ice was 15–40 cm in the Bay of Bothnia and 5–20 cm in the Gulf of Finland.

Jouni Vainio and Patrick Eriksson