The autumn of 2000 was warmer than normal and the coming of winter was delayed. In the northernmost part of the Bay of Bothnia the freeze-up did not start until the end of November, approximately three weeks later than average. But in the eastern part of the Gulf of Finland ice started to form off St. Petersburg about the usual time, that is inearly December. Elsewhere in the archipelago of the Gulf of Finland and in the Sea of Archipelago the freeze-up was delayed for more than a month until the end of January. The whole month of December was mild with only an insignificant freeze-up. The ice situation at the end of the year corresponded to the average situation in early December.

In January, weather continued to be mild which resulted in only a minor extension of the ice cover. The mild winter brought about strong southwesterly winds, which broke up the thin cover of new ice. In the Bay of Bothnia, shuga drifted against the fast ice boundary forming a brash ice barrier. At the end of January there was much less ice than average.

In early February, a cold spell set in and new ice formed along the entire Finnish coast. The Bay of Bothnia was completely covered with ice on February 7th, three weeks later than average. At the same time there was a 10–15 nautical miles wide zone of thin ice along the Sea of Bothnia coast. In the Gulf of Finland the archipelago was ice-covered and there was also ice at sea from St. Petersburg to the island of Gogland. In mid-February, a two-week mild and windy period occurred during which the ice cover diminished. In the Bay of Bothnia ice got packed east of the line Malören– Kokkola Lighthouse and in the Gulf of Finland east of the line Nerva–Seskar. Late in February the wind direction changed and the ensuing northerly winds pushed the deformed ice field out to sea, whereby a wide lead opened up along the fast ice boundary on the Finnish coast of the Bay of Bothnia. The northerly winds made the weather cold and ice formed in all sea areas. At the end of February, the ice cover reached from the northernmost part of the Bay of Bothnia to the latitude of Härnösand in the Sea of Bothnia. Farther south there was a 30–40 nautical miles wide zone of thin ice along the Finnish coast. In the Gulf of Finland the ice cover reached from St. Petersburg to the longitude of Jussarö.

In early March weather was varied with alternating short cold and mild spells. The extent of the ice cover diminished slightly. In mid-March a cold spell set in and during this spell the ice cover reached its largest extent, 129 000 km². This occurred on March 26th, which is the latest date ever recorded. The Bay of Bothnia and the Sea of Archipelago were ice-covered throughout, and in the Sea of Bothnia the ice edge ran from Agö to 30 nautical miles west of Kaskinen and then semicircularly to the Åland islands. In the Gulf of Finland the ice edge ran from Naissaar to 18 nautical miles southwest of Bengtskär and farther to Kökar. After that the ice situation gradually eased.

In April, weather was warmer than average and, as the ice was thinner than usual, the melting process was faster than average, especially in the Bay of Bothnia. The Sea of Archipelago was ice-free in mid-April, i.e. somewhat earlier than usual. In the Sea of Bothnia there was no ice left by the end of April, in the Gulf of Finland by the turn of the month. This corresponded with the average situation. The northern part of the Bay of Bothnia was ice-free in mid-May, almost two weeks earlier than normal.

The greatest thickness of the ice was as follows: 50–60 cm in the Bay of Bothnia, 30–45 cm in the Sea of Bothnia, 30 cm in the Sea of Archipelago and the western Gulf of Finland, and 35–50 cm in the eastern Gulf of Finland. At sea the thickness of the ice was 20–50 cm in the Bay of Bothnia, 10–30 cm in the Sea of Bothnia, and 10–45 cm in the Gulf of Finland.

The ice season was very much shorter than usual in all sea areas. In the Bay of Bothnia it was about four weeks shorter and in the Sea of Bothnia, Sea of Archipelago and Gulf of Finland more than four weeks shorter than average.

Simo Kalliosaari