Baltic Sea Portal

Ice conditions in the Baltic Sea vary a lot from one year to another. The maximum ice covered area varies between 52 000 and 422 000 square kilometres, which stands for 12-100 per cent of the total Baltic Sea area (including Kattegatt and Skagerrak). On average the sea ice covers 218 000 square kilometres every winter. The maximum ice cover is normally reached in late February or in March.

Maximum ice cover during different years.

The Bay of Bothnia and the eastern Gulf of Finland freeze every year

The Bay of Bothnia and the eastern Gulf of Finland gets an ice cover every year. About once every decade only a small area in the southern Baltic Sea remains ice free.

The ice formation in the Baltic Sea starts along the coasts of the northern Bay of Bothnia and the inner Gulf of Finland. This occurs usually in October-November. Thereafter the freezing spreads to the Quark, the open Bay of Bothnia and the coasts of Sea of Bothnia. In normal winters the ice gets to cover also the rest of the Sea of Bothnia, the Archipelago Sea, the whole Gulf of Finland and parts of the northern Baltic Proper.

In mild winters the Sea of Bothnia doesn’t freeze at all and the Gulf of Finland only gets a partial ice cover. In severe winters the ice reaches the Danish Sounds and the central Baltic Proper. The last area that freezes up is an area north-east of Bornholm in the Southern Baltic Sea.

Impossible to predict coming winter’s ice condition in beginning of the winter

In the beginning of the winter it is impossible to predict the ice conditions of the coming ice winter. Any reliable prediction can not be made before the end of January.

Ice melting starts in April

The melting season starts in April and proceeds from the south to the north. In the northern Baltic Proper the ice disappears in early April. By the beginning of May there is only ice left in the northern Bay of Bothnia, where also the last ice pieces melt away by the beginning of June. On average the ice season in the northern Baltic Proper lasts for less than 20 days. In the northern Bay of Bothnia there is ice for half a year.