Ice season 2025/2026 was average by extent and short

The ice season of 2025–2026 was characterized by rapid changes and ended exceptionally early. Although the ice cover at the peak of winter was among the largest in recent years, a partly record-warm spring made the ice melt quickly.

October was exceptionally mild in northern Finland, and winter started in Lapland late. The first ice formation in the northern Bay of Bothnia was observed in satellite images on 4 November. This was followed by a cold period during which new ice formed extensively along the coast of the Bay of Bothnian. The ice was approximately 20 cm at its thickest. The icebreaker Zeus began the icebreaking season in Tornio when the first traffic restrictions entered into force on 24 November. Soon after that, a milder period began and, in the beginning, there were strong winds. The winds took the ice from the Kemi fairway and largely also from Tornio.

Well into December the amount of ice did not increase significantly. There was ice practically only in the archipelago of the northern Bay of Bothnia and occasionally outside it. The first severe winter storm, Hannes, occurred on 26 December. After the storm, colder air flowed from the north, and by the New Year freezing conditions prevailed across the whole country. Ice formation started along the entire coast. Icebreaker Voima started icebreaking operations in the Bay of Bothnia on 2 January. At the turn of the year, ice covered an area of 14,000 km², corresponding to the average extent of recent decades.

A long cold period began in early January, during which cold air masses repeatedly flowed from the north into Scandinavia. High pressure dominated in the beginning of the year, bringing severe frost along the entire coast. The amount of ice increased rapidly, and the Bay of Bothnia froze over completely on 29 January. At the end of the month, also the Quark and the eastern Gulf of Finland were also ice-covered. In the Archipelago Sea, new ice formed as far as Åland.

During the long-lasting high-pressure period, record-low sea levels were also measured in several sea areas. The low water level could be seen as rocks protruded through the fast ice along the coasts. On 15 February, the amount of ice was approximately double the long-term average for the date. Despite the large ice cover, marine traffic to ports functioned well due to calm wind conditions. During the third week of February, freezing temperatures continued, but the weather became windier and the growth of ice cover in the Bothnian Sea slowed. The maximum ice extent, 181,000 km², was on 20 February. At that time, the Bay of Bothnia, the Quark, the Åland Sea, the Archipelago Sea, the Gulf of Finland and the Gulf of Riga were covered by ice. The central Bothnian Sea remained ice-free throughout the winter. In addition, new ice formed along almost the entire Swedish coast. Ice also occurred along the coasts of Poland and Germany and in the Danish straits. Based on the maximum ice extent the ice season is classified as average in severity. Finland’s entire icebreaker fleet was in operation. The last winter when ice extent has been larger was the severe winter of 2010–2011.

In March, the weather changed so that winds blew mainly from between south and west throughout the month. March was record-mild in almost the whole country. The amount of ice decreased, and particularly after mid-March the ice weakened and melted rapidly along the southern and western coasts. At the beginning of April, the Archipelago Sea was ice-free, and the ice in the Vaasa archipelago had also weakened. In the Gulf of Finland, the fairways to Finnish ports were largely open water, and there was ice remaining only east of Gogland. Nevertheless, the last ridged ice floes out at sea persisted surprisingly long, however, and the last ice floes melted northwest of Gogland on 21 April.

All the ice except that in the Bay of Bothnia had melted already, when the weather became cold again. Strong northerly winds dispersed the drift ice field in the Bay of Bothnia, accelerating melting despite the cool weather. At this stage the drift ice was already very weak, and by the end of April almost all fast ice along the Finnish coast had melted.

At the beginning of May, some fast ice still remained in the Swedish archipelago, and a narrow band of drift ice persisted out at the Bay of Bothnia. Icebreaking operations ended on 4 May, and the Baltic Sea became ice-free on 10 May. According to the statistics of the Finnish Ice Service, the Baltic Sea has been ice-free on 10 May only once before, during the winter of 2014–2015 and never earlier, so this year’s melting occurred as early as the record year.

The fast ice thickness was 20–50 cm in the Gulf of Finland and Bothnian Sea, 15–40 cm in the Archipelago Sea, 20–50 cm in the Quark and 40–80 cm in the Bay of Bothnia. Drift ice thickness was 20–50 cm in the Bay of Bothnia, 10–40 cm in the Quark and Gulf of Finland, and 5–20 cm in the Bothnian Sea.

In the Bay of Bothnia, the ice season began one and a half to two weeks later than normal and ended one and a half to just over three weeks earlier than normal.

In the northern Bothnian Sea, the ice season began a few weeks later than usual, while in the southern part it began at the normal time. In the Gulf of Finland, the ice season began on average about one week later than normal. The ice season ended from one to three weeks earlier than normal in the Bothnian Sea and Gulf of Finland.

The number of actual ice days was lower than usual in the Gulf of Bothnia. In the Gulf of Finland, there were locally slightly more ice days than usual. In the outer archipelago of the Archipelago Sea, the number of ice days was clearly above average.