The ice season 2001/2002 was mild
The northern part of the Bay of Bothnia started to freeze up in early November, about a week later than average. In Vyborg Bay in the eastern part of the Gulf of Finland, the freeze-up started slightly earlier than usual, i.e. in the second half of November, and in the rest of the Gulf about a week later than usual, late in December. By that time ice was forming also in the Archipelago Sea. The freeze-up continued throughout December as usually. By year's end the northern part of the Bay of Bothnia and the Quark were ice-covered and in the southern part of the Bay of Bothnia there was open water only in the middle part. The Archipelago Sea was also ice-covered, as was the eastern part of the Gulf of Finland from St. Petersburg to the island Hogland. Ice conditions were normal for the time of the year.
In early January weather changed, a mild period ensued and the ice cover diminished. By mid-January, the northern part of the Bay of Bothnia was ice-covered as far as Kemi Lighthouse and the southern part to the outermost islands. The wind had created heavy ridges in some places. In the Quark there was open water and the eastern part of the Gulf of Finland was ice-covered as far as the outermost islands. At the end of the month a cold spell set in and the freeze-up started anew. On January 24th, the entire Bay of Bothnia was ice-covered, almost one and a half week later than usual. The rest of the month was cold and ice formed in all sea areas.
The ice cover reached its largest extent, 102 000 km², on February 1st at the end of the cold period. The ice extended from the northern Bay of Bothnia to a point 20 nautical miles SW of Sydostbrotten, i.e. south of the Quark. In the Sea of Bothnia there was drift ice for 15-20 nautical miles off the coast whereas the Archipelago Sea was ice-covered throughout. In the Gulf of Finland the western archipelago and the whole sea area east of Hogland was ice-covered.
In February weather was variable. Early February was mild and the extent of the ice cover diminished. By mid-February, a large open water area had formed in the southern Bay of Bothnia, there was also open water in the Quark, ice in the inner skerries of the Sea of Bothnia, partly open water in the Archipelago Sea and an ice cover in the Gulf of Finland east of the island Motshnyj. Some heavily ridged areas had formed in the Bay of Bothnia. In late February and March cold spells and mild periods alternated. The ice field in the Bay of Bothnia thickened, but in all other areas most of the ice that had formed during the cold spell broke up into floes and shuga along the coast.
In April weather was warmer than average and a rapid melting process began. The Archipelago Sea and the western part of the Gulf of Finland were ice-free by mid-April, the Sea of Bothnia soon afterwards and the eastern part of the Gulf of Finland by the end of the month, which corresponded to the average situation. The Quark and the southern Bay of Bothnia were ice-free by the end of April, about a week earlier than usual. The last bits of drift ice in the northern Bay of Bothnia melted late in May, about the average time.
The greatest thickness of the fast ice was as follows: Bay of Bothnia 55–80 cm, Sea of Bothnia 30–40 cm, Archipelago Sea and the western Gulf of Finland 25-30 cm, and the eastern Gulf of Finland 35–45 cm. The ice thickness at sea was 20-50 cm in the Bay of Bothnia, 10–20 cm in the Sea of Bothnia, and 10–45 cm in the Gulf of Finland.
The ice season was about two weeks shorter than average in the Bay of Bothnia and the Quark, about the average in the archipelago of the Sea of Bothnia, and the Archipelago Sea, and about a week shorter than average in the Gulf of Finland.