The 2021/2022 ice season was mild, but long
The ice season started early and there was ice in the sea for 221 days. In the Gulf of Bothnia, the ice season was longer than usual, but in the Gulf of Finland it was shorter.
The first ice appeared in the Bay of Bothnia on 24 October 2021. Winter came to Lapland on time, even though the first half of October was warm. In the Torne River valley, the amount of precipitation in October was three times more than the usual amount. Despite the warm start of the month, when the frosts arrived, the first freeze occurred earlier than average. The first week of November was unusually mild and the amount of ice in the Bay of Bothnia decreased. At the end of the week, there was still thin shuga off Tornio. The second week of November started cold and the northwest wind was strong or near gale. It was 5...10 degrees below zero and a little new ice formed in the northern part of the Bay of Bothnia off Tornio and Liminganlahti. At this point, the sea water in the Gulf of Finland and the Gulf of Bothnia was from nearly a degree to more than two degrees warmer than average. After a short mild period, the weather cooled significantly at the end of November and the ice formation started properly. In the Bay of Bothnia in the archipelago there was thin, 5-10 cm thick level ice. Also in the Vaasa archipelago and all the way to Rauma new ice was formed. The Gulf of Finland and the Archipelago Sea were still ice-free at the end of November.
In December, the cold weather continued, and the amount of ice increased. Ice was formed also in the sheltered bays in the Gulf of Finland. The assistance restrictions for winter navigation set by the Finnish Transport Infrastructure Agency, came into force in the ports of Tornio, Kemi and Oulu, as well as in Saimaa and the Saimaa Canal. The icebreaker Otso left Katajanokka on the 3rd December and the first assistance was from Oulu on 5 December. This was about three weeks earlier than the average start of the icebreaking season. In the week number 49 there was new ice all along the coast of Finland. In the Bay of Bothnia and the Vaasa archipelago, the ice was at its thickest about 30 cm.
December turned out to be colder than usual and the cold continued until the Epiphany. The ice covered area grew to 77,460 km² on 11th January. The Bay of Bothnia froze almost entirely, including the Quark. In the Gulf of Finland there was ice from St. Petersburg to Gogland and there was thin ice off the coast of Finland to the line Helsinki lighthouse–Gogland. New ice was also formed for a while in the fairways in the Archipelago Sea. The fast ice thickness in the Bay of Bothnia was 20-35 cm, in the Quark 10-35 cm, in the Bothnian Sea 10-25 cm and in the Gulf of Finland 10-30 cm. Icebreaking had started in the Gulf of Finland as well. After this, the weather abated and became very windy. A southwesterly storm on 12 January in the Bay of Bothnia caused that all the drift ice compressed into an arch off Kemi I lighthouse. The ice field consolidated and became difficult to force. The Föhn wind raised the temperatures well over zero. Until the end of the month, the weather varied between mild southwestern winds followed by brief colder periods. During the colder periods, new ice was formed, but the ice covered area in the Baltic Sea did not significantly increase. The outer sea of the Bay of Bothnia still remained open.
February started cold and the largest ice covered area of the winter was reached on 4 February when there was 93,000 km² ice. Measured by the extent of the ice, the ice season is classified as mild. At that time, the Bay of Bothnia was completely frozen. In the Bothnian Sea, there was thin new ice off the coastal fast ice. Also, in the Archipelago Sea, there was thin ice in the inner archipelago. In the Gulf of Finland, the ice reached from St. Petersburg approximately to the line Helsinki - Tallinn. In Estonia, the coast, Väinameri and Pärnu Bay were frozen. In the southern Baltic Sea, there was ice for a few weeks between December and January on the southern coast of Sweden and on the coast of Germany. After the 5th of February, the rest of the month was mild and rainy. February was record-breaking rainy in the eastern part of the Gulf of Finland. This was reflected in the thickness of the ice as an increased proportion of snow-ice. About half of the total thickness of the ice in the eastern Gulf of Finland consisted of snow-ice.
At the beginning of March, the open sea of the Gulf of Finland was ice-free. There was drift ice only east of Haapasaari. In the Bay of Bothnia, a wide lead ran along the Swedish coast. The northernmost harbours in Finland had to be accessed through ridged ice. As March progressed, there were no major changes in the ice situation. The month was dry and clear. There was that much night frost that even in the Gulf of Finland new ice was formed widely on a few occasions. The ice thickness increased to 85 cm in the Bay of Bothnia. In the Vaasa archipelago and in the eastern part of the Gulf of Finland, the ice was at its thickest 50-60 cm. In the Bothnian Sea and the Southwest Archipelago, the ice was 20-45 cm thick. At the end of the month, the ice extent was close to the long-term average of the time. In the last days of March, colder air started to flow from the north, and from then on there was more ice than average. At the same time, the softening of the ice started by the warm days slowed down. The northern winds also caused the ice field in the southern part of the Bay of Bothnia to consolidate well.
April started very cold. The northern winds had pushed the drift ice field of the Bay of Bothnia further south. From Kemi I lighthouse to the west and along the western part of the Bay of Bothnia to the south ran a lead in which level ice quickly formed. There was also new ice off Kotka and Hamina. Despite the cold weather, the fast ice of the western part of the Gulf of Finland and the Archipelago Sea rotted. However, the lead on the Swedish side was closed in the second week, when the east wind pushed the ice momentarily to the west. In the middle of the month, however, there was again a close pack ice field off the fairways leading to the ports of the southern part of the Bay of Bothnia. Instead, as the thinner ice melted, a large open water area was created in the northern part of the Bay of Bothnia, and it remained until the end of the season. The thickest ice at open sea remained south of Marjaniemi's latitude. The fast ice in the Bothnian Sea rotted. In the Gulf of Finland, icebreaking season ended on 11 April. Still 6 Finnish and 4 Swedish breakers were working in the Quark and the Bay of Bothnia. In week 16, the weather warmed up and the ice in the Vaasa archipelago rotted. The amount of ice in the Bay of Bothnia also decreased, and at the end of the month all drift ice was practically in the southern part of the Bay of Bothnia.
The first 3 weeks of May were colder than average in the Bay of Bothnia and the melting of the ice was slow. The Archipelago Sea and the Bothnian Sea were free of ice on the 30th April, and the Gulf of Finland a few days later. The fast ice in the archipelago of the Bay of Bothnia disappeared on 16 May, after which the remaining fast ice at open sea persisted between Raahe and Kalajoki until 3rd June. All in all, there was ice in the Baltic Sea for 221 days.
The first freeze-up occurred earlier than usual on the coasts. In the most northern part of the the Bay of Bothnia, the freezing occurred approximately at the usual time, but elsewhere in the Gulf of Bothnia, a week to four weeks earlier than usual. In the Gulf of Finland, the first freeze-up occurred about two to four weeks earlier than usual.
The time of the final ice disappearance, compared to the usual, varied greatly. In the northern part of the Bay of Bothnia, the ice disappeared a few days later than usual, while in the Quark it happened more than a week earlier than usual. In the northern part of the Bothnian Sea, the ice disappeared from a week to about two weeks later than usual, and in the southern part from a week to two weeks earlier than usual. In the Gulf of Finland, the ice disappeared 12–17 days earlier than usual.
The amount of ice days were 3–36 days more than usual in the Gulf of Bothnia, and 23–36 days less in the Gulf of Finland, except for the easternmost part, where the ice seasons length was as usual.
The maximum fast ice thickness varied between 30–85 cm in the Bay of Bothnia, 30–60 cm in the Bothnian Sea, 15–40 cm in the Archipelago Sea and 15–60 cm in the Gulf of Finland. The thickness of the ice in the open sea was at its thickest in the Bay of Bothnia 20–70 cm, in the Bothnian Sea 5–35 cm, and in the Gulf of Finland 15–30 cm.
The distance ships needed to navigate in ice to the ice edge on 4th February 2022 was 194 nautical miles from Kemi. From St. Petersburg the distance to the ice edge was 154 nautical miles, of which 25 nautical miles in new ice.