The ice season 1999/2000 was mild
The freezing process in the northern part of the Bay of Bothnia started in late November, more than a week later than usual. In the easternmost part of the Gulf of Finland, that is off St. Petersburg and in the Bay of Vyborg, ice formation started slightly earlier, in mid-November. Freezing was very slow during the whole of November and in early December. However, during the first half of December so much new ice was formed in the northernmost part of the Bay of Bothnia that the ice situation in mid- December could be characterized as fairly normal. The second part of December was mild and windy and ice was packed against the fast ice edge along the coast of the northern part of the Bay of Bothnia.
In early January new ice was forming in the Gulf of Finland archipelago east of Loviisa, two weeks later than normal. During the first half of January the freezing process proceeded slowly, but in the middle of the month there was a cold spell and new ice was formed both in the Gulf of Bothnia and the Gulf of Finland. The Bay of Bothnia was completely covered with ice on January 26th, ten days later than average. Simultaneously there was a 10-mile-wide belt of new ice in the Sea of Bothnia and an ice cover reaching from Hogland to the eastern end of the Gulf of Finland. At the end of January strong winds broke up the ice field in the Bay of Bothnia and ice was packed off the Finnish coast forming a heavily ridged ice belt at the fast ice edge.
In early February new ice was forming in the Bay of Bothnia from time to time. It was soon broken up by winds forcing it to the northeast, up against the ice edge. In the Gulf of Finland the ice situation was eased to the extent that, by mid-february, there was ice only east of the longitude of Seskar. In mid- February a new cold spell set in and ice was formed in all sea areas. During this period, i.e. on February 24th, the ice cover reached its largest extent, 96 000 km², comprising the whole of the Bay of Bothnia, the Quark and the Sea of Archipelago. In the Sea of Bothnia there was a 5–15 -mile-wide belt of thick drift ice off the Finnish coast as well as off Gävle on the Swedish coast. In the Gulf of Finland the ice edge ran from Hanko via Kalbådagrund to Vaindlo and from there to the Estonian coast. At the end of February the ice situation was eased rapidly, especially in the Sea of Bothnia and in the Gulf of Finland, where winds broke up the thin ice forming a brash barrier along the Sea of Bothnia coast as well as in the archipelago of the western Gulf of Finland, and a ridged ice zone in the eastern part of the Gulf of Finland. image.
In early March frost set in and new ice was formed in all sea areas. By mid-March the weather got milder again and the ice started to rot and melt both in the Sea of Bothnia and the Gulf of Finland. In the Bay of Bothnia, on the other hand, strong winds kept a heavily ridged ice field off the Finnish coast obstructing navigation. April was warmer than average and the ice continued to rot and melt. The Sea of Archipelago and the western part of the Gulf of Finland were the first areas to become ice-free. As usual, this happened in the second part of April. The Sea of Bothnia became ice-free at the end of April and the Quark in early May, at the average time. The eastern part of the Gulf of Finland became ice-free late in April, about a week later than usual. In May the weather was changeable and the melting process in the Bay of Bothnia was very slow. The fast ice in the coastal areas had melted by mid-May but a heavily ridged drift ice area ranging from Kemi to Raahe remained stationary to the end of May. The last ice floes, situated off the island of Hailuoto in the Bay of Bothnia, melted on June 11th, two weeks later than average.
The greatest thickness of the fast ice was 50–85 cm in the Bay of Bothnia, northern part, and 30–60 cm in the southern part, 20–45 cm in the Sea of Bothnia, 10–25 cm in the Archipelago Sea and in the western part of the Gulf of Finland and 20–45 cm in the eastern part of the Gulf of Finland. The ice thickness on the open sea was 30–70 cm in the Bay of Bothnia, northern part, and 10–40 cm in the southern part, 5–20 cm in the Sea of Bothnia and 20–50 cm in the eastern part of the Gulf of Finland.
The ice season was about a week shorter than average in the northern part of the Bay of Bothnia, more than a week longer than average in the southern part of the Bay of Bothnia and about a week longer than average off the coast in the Sea of Bothnia. In the Sea of Archipelago, on the other hand, the ice season was almost three weeks, in the archipelago of the western part of the Gulf of Finland more than four weeks and in the eastern part of the Gulf of Finland about two weeks shorter than average.