In the Baltic Sea ice conditions vary greatly. The annual ice cover is at its greatest between January and March, usually around the end of February/beginning of March.
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.
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.
Baltice.org is a single access point to reliable and up to date information related to winter navigation in the Baltic Sea area. This site gathers information and instructions from icebreaking authorities from all the Baltic Sea countries.
The aim of the site is to extend the knowledge of winter navigation and prevailing conditions in the area during ice season.
The Winter Navigation Unit at the Finnish Transport Agency has compiled general instructions for winter navigation in Finnish and English - Instructions for winter navigation operators