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Record-short winter in Helsinki; ice dangerously thin on sea


Record-short winter in Helsinki; ice dangerously thin on sea
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By Anu Ilomäki
     
      The past winter is likely to be the shortest ever recorded by the Finnish Meteorological Institute. Up until now, the shortest winter in the statistics that have been kept from 1961 was in 1991-1992. Now it appears that this year, the winter is three days shorter than the previous record.
      The thermal winter is considered to be over when the average temperature stabilises at above freezing. Occasional night frosts that might occur later are not counted as signs of a return of winter.
      The first and last days of winter can only be determined in retrospect, when temperatures can be seen to have stabilised.
      Barring a sudden cold snap, the winter can be seen to have ended on the 28th of February this year. Normally, the winter lasts for about a month longer, ending in late March.
     
This year the length of the winter in Helsinki was about a third of the length of a normal one. Whereas the average length of winter in Helsinki is 120 days, this year it was just 40 days.
      The winter began two months later than usual - on January 19th, when the average temperature stabilised below freezing.
      "This winter has been unusual. Average temperatures for January were really high, and there were mild temperatures all the way to mid-January", describes Hanna Tietäväinen, meteorologist at the Meteorological Institute.
      The average temperature for Helsinki in December was four degrees, which is six degrees higher than normal. Tietäväinen feels that it is likely that this year’s winter will set the tone for winters to come.
      "Studies indicate that winters are getting shorter, and will be mild as this one was."
     
Walking on ice on the sea should be avoided, as the short winter has meant that the sea has frozen very unevenly.
      In normal winters, the cold penetrates the ice all the way to the bottom layer, which causes it to freeze evenly. Now ice off Helsinki is up to between 25 and 40 centimetres thick, but next to the thick parts, there are often areas which are just one or two centimetres thick.
      The Finnish Institute of Marine Research warns that it is impossible for a casual observer to tell where the ice is too thin to walk on. Water on the surface of the ice can be deceptive, as it makes the ice appear stronger than it really is.
      "Even if there are cold temperatures at night, the ice is gradually becoming weaker, because the sun is shining powerfully. The sun can melt ice through layers of cloud as well", says Jouni Vainio, a researcher at the Finnish Institute of Marine Research.
     
Helsingin Sanomat / First published in print 17.3.2007


ANU ILOMÄKI / Helsingin Sanomat
anu.ilomaki@hs.fi


  20.3.2007 - THIS WEEK
 Record-short winter in Helsinki; ice dangerously thin on sea

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