The ice season of 2022/2023 was mild
In the Bay of Bothnia, the ice season was longer than average, while in the Gulf of Finland it was shorter. The peak of the ice season was experienced on March 12, when ice occurred in an area of 81,000 km².
October 2022 was warmer than usual, and also the beginning of November was milder than usual. In the third week of November, the weather got colder and the first ice off Tornio and Kemi was observed in satellite images on November 15. At this stage, the water temperatures in the central parts of the Bay of Bothnia, the Bothnian Sea and the Gulf of Finland were about one degree higher compared to the previous year. The amount of ice gradually increased as the freezing weather continued, and at the end of November there was ice not only on the coast of the northern part of the Bay of Bothnia, but also off Raahe, in the Pietarsaari and Vaasa archipelagos, and in the Gulf of Finland off St. Petersburg and in the Gulf of Vyborg. At this point, the thickness of the ice in Tornio was a good 10 cm.
On December 12, the first assistance restrictions for Tornio and Kemi came into force. New ice formed in the Vaasa archipelago, and Estonian coastal waters also began to freeze. Icebreaker Otso started icebreaking assistance on December 15. In December, the amount of ice increased slowly. It snowed a lot, especially on the south coast. The coldest period was during the third week of December, when ice also formed in the Southern Baltic Sea, along the coasts of Germany and Poland. At this point, the ice-covered area was about 30,000 km². The icebreaker Kontio left on December 26 as the second icebreaker from Helsinki towards the Bay of Bothnia. At the end of the month, two Finnish and two Swedish icebreakers were operating in the Bay of Bothnia. In the Gulf of Finland, the Archipelago Sea and the Bothnian Sea there was thin ice in the inner archipelago. In the Vaasa archipelago and the northern part of the Bay of Bothnia, the ice thickness was 10–25 cm. December ended mildly, and the German ice had almost melted by the end of the year.
At the beginning of January, the weather got colder for a while, and on January 6 it was 20 degrees below zero in places. However, the wind soon turned to blow from the south and the weather got milder. The temperature rose above zero in all sea areas. The southerly wind compacted the ice field in the eastern part of the Gulf of Finland, and the icebreaking assistance in the Gulf of Finland started on January 10. The growth of the ice-covered area halted until February. At the beginning of week 6, the ice covered an area of more than 60,000 square kilometres, but the stormy south-westerly wind compacted the ice in the Bay of Bothnia. At the end of February, there were easterly winds, the weather was cold, and the amount of ice increased again. The Bay of Bothnia froze over completely and there was also thin drifting ice all over the Quark. In the Gulf of Finland, the edge of new ice reached the western side of Gogland. At this stage, the ice thickness was at most 60 cm in the Bay of Bothnia, 35 cm in the Quark and 25 cm in the Bothnian Sea and the Gulf of Finland.
From mid-February to mid-March, the total amount of ice increased steadily. This was helped by the fact that March was clearly colder than average, especially in Northern Finland. The largest ice-covered area of the season was reached on March 12, when there was 81,000 km² of ice. In the south, the weather was milder and the amount of ice in the Gulf of Finland did not increase anymore. In the first half of April, the Gulf of Finland was hit by easterly winds for more than a week. The drift ice off the Gulf of Vyborg drifted westward, and at its westernmost point in the open sea the drift ice reached the longitude of Porvoo before melting. The fast ice was already rotten at this point. The Bothnian Sea and the Gulf of Finland were ice-free on April 26. Due to the prevailing south-easterly winds at the end of April, the drift ice in the Bay of Bothnia moved to the west, and off the coast on the Finnish side an area easy to navigate remained for a long time from the lighthouse of Kemi 2 to Kallan off Pietarsaari.
At the beginning of May, drift ice in the Bay of Bothnia melted quickly. By May 14th all that was left was the coastal fast ice, which had also become rotten. The last ice in the Vaasa archipelago had melted a few days earlier. On the Kemi – Tornio fairway, some ridged ice floes with a thickness of more than a meter remained for a long time. Icebreaker Kontio was on duty in the area until May 24. The last assistance restrictions were removed from Kemi and Tornio on May 27 and the Baltic Sea was ice-free on May 29.
The ice season 2022–23 was mild in terms of the ice extent. However, the Bay of Bothnia did freeze over, and there was fast ice along the entire Finnish coast. In the Gulf of Finland, drift ice remained east of Gogland practically throughout the winter. In the Archipelago Sea, the outer archipelago remained open. Similarly, in the Bothnian Sea, not much drift ice was found outside of the coastal ice. In the Bay of Bothnia, the ice field was ridged in places, but not as much as in some other mild winters.
In the Bay of Bothnia, the ice season started about a week later than usual and ended more than a week later than usual. In the Quark, the ice season started a few days later than usual and ended a week and a half to two weeks later than usual. In the Bothnian Sea, the ice season started at the usual time and ended about a week earlier than usual. In the western Gulf of Finland, ice occurred at the usual time, but on fewer days than usual. In the central Gulf of Finland, the ice season started a few days earlier than usual and ended at the usual time. In the eastern Gulf of Finland, the ice season started more than a week later than usual and ended at the usual time.
There were more ice days than average in the Bay of Bothnia, the Quark and the northern Bothnian Sea, while there were clearly fewer ice days in the southern Bothnian Sea and the Gulf of Finland. The maximum thickness of fast ice varied between 20–70 cm in the Bay of Bothnia, 10–30 cm in the Bothnian Sea, 5–20 cm in the Archipelago Sea and 10–40 cm in the Gulf of Finland. The thickness of the ice in the open sea was at its thickest 20–65 cm in the Bay of Bothnia and 10–30 cm in the Gulf of Finland.
The distance that vessels had to navigate through ice on 12 March 2023 was 189 nautical miles from Kemi and 118 nautical miles from St. Petersburg to the ice edge. Correspondingly the navigation distance in ice 15 cm thick or more was 126 nautical miles and 16 nautical miles.