Only a fortnight ago it looked as if the sea ice in the Baltic will end the season according average as indicated in Fig 1, showing the ice cover on the 7th Feb. (jäätä) vs normal ( 11/Feb, right). On week later on the 14th the Gulf of Bothnia and the Gulf of Finland were fully covered with ice for the first time this year (Fig. 2 ; Finish ice map 14.Feb.- No.89). Last year this situation appeared early March 2010. (see last paragraph) However during the last 10 days the ice extended quickly southwards. About 250,000 square kilometres of the Baltic Sea are now covered by ice according to the Swedish Meteorological and Hydrological Institute (SMHI). (h/t Pierre Gosselin) The last time hat so much of the Baltic was frozen was the winter of 1986-87, when ice covered nearly 400,000 square kilometres of the sea's surface. (see: http://www.thelocal.se/32262/20110225/ )
The quick extension over the last few days, is due to low temperature from Siberia to the Baltic countries. The cold is still present and forecast indicate hash freezing conditions (between high –3°C and low: -15°C) until early March. That will presumably mean that the 400,000 square kilometres of 1986/87 will be succeeded soon.
The sudden increase during the last few days is not so much an surprise if one recalls that Northern Europe from Great Britain to Murmansk experienced presumably the coldest December month fro many decades. For the UK, 120 years is claimed. In particularly the sea ice conditions as per the 31 December 2010 had been extraordinary, and I am not aware that such a situation has ever been reported from the Skagerrak for December. At that time all conditions indicated for a record to come. For details see: “Record Sea Ice conditions for the Baltic Sea region ahead?” at : http://www.2007seatraining.de/Archiv/dec2_10.html Instead the January and February had been modest in western Europe, only north-east of the river Oder the temperatures dropped sharply in February. The cold reached the Baltic countries at about 14th February.
Last year the winter condition had been deep wintry since the Climate Summit in Copenhagen in mid December 2009. Despite this severe condition for 10 weeks, the ice cover remained in the range of normal until the end of February 2010. Details here: “The coldest winter in the Baltic Sea region for 30 years, but where is sea ice in winter 2009/10?” http://www.oceanclimate.de/Archiv/maerz_10.html . This year raises even more questions science should answer. For example which role plays shipping with regard to preventing the forming of sea ice, or even contributing to the freezing process. The matter is discussed in German (10 April 2008) at: http://www.ozeanklima.de/Archiv/april_08.html .